SwePub - sökning: WFRF:(Sjöberg Britt Marie)

Numrering	Referens	Omslagsbild	Hitta
1.	Drottz-Sjöberg, Britt-Marie, et al. (författare) Knowledge and risk perception among nuclear power plant employees 1991 Ingår i: Risk Analysis. - : Wiley: 24 months. - 1539-6924 .- 0272-4332. ; 11:4, s. 607-618 Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract This is a study of knowledge, risk perception, and attitudes among nuclear power plant employees. A total of 236 persons participated, belonging to 10 different professional groups and working at two Swedish power plants. Job-related radiation risks were judged about average as compared to a number of other risks. On the whole, the participants in the study were satisfied with the measures of safety at work, but there were some exceptions to this rule, especially among those hired for temporary jobs through external contractors. The experience of job-related radiation risks was related to the level of knowledge about radiation and its risks: those who knew less experienced larger risks. General level of anxiety did not correlate with risk perception. The latter was accounted for mainly by perceived radiation risks. Job satisfaction was more strongly related to perceived conventional job risks than to nuclear risks. Risk ratings were related to how subjects defined the concept of risk. Those who stressed consequences as part of their risk definition gave higher risk ratings.
2.	Drottz-Sjöberg, Britt-Marie, et al. (författare) Psychological reactions to cancer risks after the Chernobyl accident 1987 Ingår i: Medical Oncology. - : Humana Press. - 1559-131X .- 1357-0560. ; 4:3-4, s. 259-271 Tidskriftsartikel (refereegranskat)abstract This is a report on an investigation of people's reactions to the Chernobyl accident. Interviews and, mail surveys were conducted in July-September 1986 with pregnant women, parents of newborn children, farmers, adolescents and men who were not parents, in various areas of Sweden, differing as to the amount of Chernobyl fallout they had received. The accident had probably doubled the number of people who were negative to nuclear power in the most affected area. Radiation risks were highly salient in most groups. Areas differed in the expected direction, people in the more, exposed areas being more concerned. Women were more worried and more negative to nuclear power than men while adolescents appeared to be the group least affected by the accident. Farmers were also strongly opposed to nuclear power and concerned about its risks. Nuclear attitude could be well accounted for by attitude statements and rated basic life values. It was quite stable over a 1 month period.
3.	Drottz-Sjöberg, Britt-Marie, et al. (författare) Risk perception and worries after the Chernobyl accident 1990 Ingår i: Journal of Environmental Psychology. - : Elsevier. - 0272-4944. ; 10:2, s. 135-149 Tidskriftsartikel (refereegranskat)abstract This is a study of reactions in selected groups of the Swedish population to the Chernobyl accident. Data were collected in September 1986, from 3 regions in the country which had been exposed in various degrees to radioactive fallout. In each region samples of farmers, adolescents, persons who had had a child just before or after the accident, and men who were not registered as legal custodians of children, were approached with a mail questionnaire. It was found that attitudes to nuclear power were predominantly negative, that the risks associated with radiation and nuclear power were rated among the worst risks, and that residents of the most exposed region (Gavle) reported being worried about injury from radiation twice as often as others. A sub-group of decisive opponents of nuclear power was identified. It was 15 times larger than the corresponding sub-group of decisive proponents. New parents and farmers were quite negative to nuclear power, a finding discussed in relation to their responsibilities for food production and care for others.
4.	Ohlson, Johan, et al. (författare) A method to find tissue-specific novel sites of selective adenosine deamination 2005 Ingår i: Nucleic Acids Research. - 0305-1048. ; 33:19, s. 7- Tidskriftsartikel (refereegranskat)
5.	Sjöberg, Lennart, et al. (författare) Adolescents' attitudes to nuclear power and radioactive wastes 1991 Ingår i: Journal of Applied Social Psychology. - : Wiley: 12 months. - 1559-1816 .- 0021-9029. ; 21:24, s. 2007-2036 Tidskriftsartikel (refereegranskat)abstract High school students (N = 380) reported their attitude to nuclear power and rated various risks: nuclear and non-nuclear, personal and societal. The focus of the study concerned risks related to handling and disposal of radioactive waste. It was found that conventional personal risks obtained lower risk ratings than risks to society and risks related to accidents in the handling and disposal of radioactive waste. In general, items which made reference to radiation were rated higher than items which did not mention this aspect. Female students most often rated risk higher than did male students. Persons worried about nuclear power emphasized risks of accidents and waste disposal as problems, whereas those who did not worry trusted those in charge and saw nuclear power as quite safe, stressing its basis in advanced technological knowledge and skill, Students specializing in economics or technology were the least concerned about nuclear power risks and had the most positive attitudes to nuclear power. The results of the study are discussed in relation to risk perception discrepancies of experts and the public. We suggest that future experts will be recruited from groups that have, already in adolescence, established beliefs about nuclear technology risks that are lower than those of other groups. Compared to a national sample dominated by adults, the adolescents, especially boys, held more positive attitudes to nuclear power and rated risks of nuclear technology lower than adults.
6.	Andersson, Jessica, et al. (författare) Two Active Site Asparagines Are Essential for the Reaction Mechanism of the Class III Anaerobic Ribonucleotide Reductase from Bacteriophage T4 2001 Ingår i: The Journal of Biological Chemistry. ; 44, s. 40457-40463 Tidskriftsartikel (refereegranskat)
7.	Andersson, Kjell, et al. (författare) Comparison of Approaches to Risk Governance 2009 Rapport (övrigt vetenskapligt/konstnärligt)
8.	Andersson, Martin E, et al. (författare) Structural and mutational studies of the carboxylate cluster in iron-free ribonucleotide reductase R2. 2004 Ingår i: Biochemistry. - 0006-2960. ; 43:24, s. 7966-72 Tidskriftsartikel (refereegranskat)abstract The R2 protein of ribonucleotide reductase features a di-iron site deeply buried in the protein interior. The apo form of the R2 protein has an unusual clustering of carboxylate side chains at the empty metal-binding site. In a previous study, it was found that the loss of the four positive charge equivalents of the diferrous site in the apo protein appeared to be compensated for by the protonation of two histidine and two carboxylate side chains. We have studied the consequences of removing and introducing charged residues on the local hydrogen-bonding pattern in the region of the carboxylate cluster of Corynebacterium ammoniagenes and Escherichia coli protein R2 using site-directed mutagenesis and X-ray crystallography. The structures of the metal-free forms of wild-type C. ammoniagenes R2 and the mutant E. coli proteins D84N, S114D, E115A, H118A, and E238A have been determined and their hydrogen bonding and protonation states have been structurally assigned as far as possible. Significant alterations to the hydrogen-bonding patterns, protonation states, and hydration is observed for all mutant E. coli apo proteins as compared to wild-type apo R2. Further structural variations are revealed by the wild-type apo C. ammoniagenes R2 structure. The protonation and hydration effects seen in the carboxylate cluster appear to be due to two major factors: conservation of the overall charge of the site and the requirement of electrostatic shielding of clustered carboxylate residues. Very short hydrogen-bonding distances between some protonated carboxylate pairs are indicative of low-barrier hydrogen bonding.
9.	Aurelius, Oskar, et al. (författare) The Crystal Structure of Thermotoga maritima Class III Ribonucleotide Reductase Lacks a Radical Cysteine Pre-Positioned in the Active Site 2015 Ingår i: PLOS ONE. - : Public Library of Science (PLoS). - 1932-6203. ; 10:7 Tidskriftsartikel (refereegranskat)abstract Ribonucleotide reductases (RNRs) catalyze the reduction of ribonucleotides to deoxyribonucleotides, the building blocks for DNA synthesis, and are found in all but a few organisms. RNRs use radical chemistry to catalyze the reduction reaction. Despite RNR having evolved several mechanisms for generation of different kinds of essential radicals across a large evolutionary time frame, this initial radical is normally always channelled to a strictly conserved cysteine residue directly adjacent to the substrate for initiation of substrate reduction, and this cysteine has been found in the structures of all RNRs solved to date. We present the crystal structure of an anaerobic RNR from the extreme thermophile Thermotoga maritima (tmNrdD), alone and in several complexes, including with the allosteric effector dATP and its cognate substrate CTP. In the crystal structure of the enzyme as purified, tmNrdD lacks a cysteine for radical transfer to the substrate pre-positioned in the active site. Nevertheless activity assays using anaerobic cell extracts from T. maritima demonstrate that the class III RNR is enzymatically active. Other genetic and microbiological evidence is summarized indicating that the enzyme is important for T. maritima. Mutation of either of two cysteine residues in a disordered loop far from the active site results in inactive enzyme. We discuss the possible mechanisms for radical initiation of substrate reduction given the collected evidence from the crystal structure, our activity assays and other published work. Taken together, the results suggest either that initiation of substrate reduction may involve unprecedented conformational changes in the enzyme to bring one of these cysteine residues to the expected position, or that alternative routes for initiation of the RNR reduction reaction may exist. Finally, we present a phylogenetic analysis showing that the structure of tmNrdD is representative of a new RNR subclass IIIh, present in all Thermotoga species plus a wider group of bacteria from the distantly related phyla Firmicutes, Bacteroidetes and Proteobacteria.
10.	Berggren, Gustav, et al. (författare) Compounds with capacity to quench the tyrosyl radical in Pseudomonas aeruginosa ribonucleotide reductase 2019 Ingår i: Journal of Biological Inorganic Chemistry. - : Springer Science and Business Media LLC. - 0949-8257 .- 1432-1327. ; 24:6, s. 841-848 Tidskriftsartikel (refereegranskat)abstract Ribonucleotide reductase (RNR) has been extensively probed as a target enzyme in the search for selective antibiotics. Here we report on the mechanism of inhibition of nine compounds, serving as representative examples of three different inhibitor classes previously identified by us to efficiently inhibit RNR. The interaction between the inhibitors and Pseudomonas aeruginosa RNR was elucidated using a combination of electron paramagnetic resonance spectroscopy and thermal shift analysis. All nine inhibitors were found to efficiently quench the tyrosyl radical present in RNR, required for catalysis. Three different mechanisms of radical quenching were identified, and shown to depend on reduction potential of the assay solution and quaternary structure of the protein complex. These results form a good foundation for further development of P. aeruginosa selective antibiotics. Moreover, this study underscores the complex nature of RNR inhibition and the need for detailed spectroscopic studies to unravel the mechanism of RNR inhibitors.
11.	Berggren, Gustav, et al. (författare) Homo- and Heterometallic Dinuclear Manganese Proteins : Active Site Assembly 2017 Ingår i: Metalloprotein Active Site Assembly. - : John Wiley & Sons. - 9781119159834 ; , s. 215-233 Bokkapitel (refereegranskat)
12.	Berggren, Gustav, et al. (författare) Semiquinone-induced Maturation of Bacillus anthracis Ribonucleotide Reductase by a Superoxide Intermediate 2014 Ingår i: Journal of Biological Chemistry. - 0021-9258 .- 1083-351X. ; 289:46, s. 31940-31949 Tidskriftsartikel (refereegranskat)abstract Background: Activation of ribonucleotide reductase Ib depends on the flavodoxin-like maturase NrdI.Results: The redox properties of Bacillus anthracis NrdI allow isolation of the semiquinone state, NrdI(sq), which can catalyze formation of the manganese-tyrosyl radical cofactor.Conclusion: The maturation capacity of NrdI(sq) provides evidence that Mn-NrdF is activated via a superoxide radical.Significance: Novel antibiotics may be designed to selectively target the maturation mechanism.
13.	Bergquist, Helen, 1979-, et al. (författare) Pkd1 DNA triplex stabilization by benzoquinoquinoxaline derivatives Tidskriftsartikel (refereegranskat)
14.	Berner, Boel, 1945-, et al. (författare) Inledning 2008 Ingår i: Samhällsforskning 2008. Betydelsen för människorna, hembygden och regionen av ett slutförvar för använt kärnbränsle. - Stockholm : SKB. Bokkapitel (populärvet., debatt m.m.)
15.	Berner, Boel, 1945-, et al. (författare) Inledning 2007 Ingår i: Samhällsforskning 2007. Betydelsen för människorna, hembygden och regionen av ett slutförvar för använt kärnbränsle. - Stockholm : SKB. Bokkapitel (populärvet., debatt m.m.)abstract
16.	Berner, Boel, 1945-, et al. (författare) Inledning 2006 Ingår i: Samhällsforskning 2006. Betydelsen för människorna, hembygden och regionen av ett slutförvar för använt kärnbränsle. - Stockholm : SKB. Bokkapitel (populärvet., debatt m.m.)abstract
17.	Berner, Boel, 1945-, et al. (författare) Inledning 2005 Ingår i: Samhällsforskning 2005. Betydelsen för människorna, hembygden och regionen av ett slutförvar för använt kärnbränsle. - Stockholm : SKB. - 9197560634 Bokkapitel (populärvet., debatt m.m.)
18.	Berner, Boel, et al. (författare) Introduktion 2009 Ingår i: Samhällsforskning 2009. - Stockholm : SKB. - 9789197786287 ; , s. 4-17 Bokkapitel (populärvet., debatt m.m.)
19.	Berner, Boel, 1945-, et al. (författare) Samhällsforskningen 2004-2009. Teman, resultat och reflektioner. 2009. - 1 Bok (övrigt vetenskapligt/konstnärligt)
20.	Berner, Boel, 1945-, et al. (författare) Social Science Research 2004-2010 : Themes, results and reflections (on nuclear waste issues) 2011 Bok (övrigt vetenskapligt/konstnärligt)abstract Denna skrift är upplagd på följande sätt. Efter detta introduktionskapitel ger vi i kapitel 2 en presentation av de viktigaste resultaten inom de fyra områdena: Socioekonomisk påverkan – samhällsekonomiska effekter, Beslutsprocesser – governance, Opinioner och attityder – psykosociala effekter samt Omvärldsförändringar. Vi sammanfattar här de olika projektens bidrag (för presentationer av respektive projekt, se bilaga 2). För originalarbeten, rapporter och andra publikationer inom programmet se litteraturlistan i bilaga 7 eller SKB:s webbplats.I kapitel 3 för vi sedan ett mer diskuterande resonemang kring några centrala teman av betydelse för förståelsen av kärnavfallsfrågans sociala och samhälleliga konsekvenser. Det är teman som aktualiserats av och även belysts i de olika projekten. Vi har valt att fokusera på frågor om samhälleliga förändringsmönster, om olika bilder av nyttan av ett slutförvar för använt kärnbränsle och risker i lokalsamhället och nationellt, på opinioner och attityder på olika nivåer, samt på slutförvarets långsiktiga betydelse. Vi tar upp dessa frågor som just frågor, för fortsatt forskning och diskussion. I kapitel 4 ges slutligen en sammanfattande värdering av samhällsprogrammets verksamhet och behoven av framtida forskning.I bilagorna 4–6 ges en bild av situationen i världen beträffande kärnkraft och avfallshantering.
21.	Brännvall, Mathias, 1973- (författare) Metal ion cooperativity in Escherichia coli RNase P RNA 2002 Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract RNase P is an essential ribonuclease responsible for removal of the 5’ leader of tRNA precursors. Bacterial RNase P consists of an RNA subunit and a small basic protein. The catalytic activity is associated with the RNA subunit, i.e. bacterial RNase P RNA is a ribozyme. The protein subunit is, however, essential for activity in vivo. RNase P RNA, as well as the holoenzyme, requires the presence of divalent metal ions for activity. The aim of this thesis was to increase our understanding of the catalytic mechanism of RNase P RNA mediated cleavage. The importance of the nucleotides close to the cleavage site and the roles of divalent metal ions in RNase P RNA-catalyzed reaction were investigated. Escherichia coli RNase P RNA (M1 RNA) was used as a model system.It was shown that different metal ions have differential effects on cleavage site recognition. Cleavage activity was rescued by mixing metal ions that do not promote cleavage activity by themselves. This suggests that efficient and correct cleavage is the result of metal ion cooperativity in the RNase P RNA-mediated cleavage reaction. The results suggested that one of the metal ions involved in this cooperativity is positioned in the vicinity of a well-known interaction between RNase P RNA and its substrate. Based on my studies on how different metal ions bind to RNA and influence its activity we raise the interesting possibility that the activity of biocatalysts that depend on RNA for activity are up- or downregulated depending on the intracellular concentrations of the bulk biological metal ions Mg2+ and Ca2+.The nucleotides upstream of the cleavage site in the substrate were found to influence the cleavage efficiency. This was not exclusively due to intermolecular base pairing within the substrate but also dependent on the identities of the nucleotides at position –2 and –1. The strength of the base pair at position –1/+73 was demonstrated to affect cleavage efficiency. These observations are in keeping with previous suggestion that the nucleotides close to the cleavage site are important for RNase P cleavage. We conclude that the residue at -1 is a positive determinant for cleavage by RNase P. Hence, my studies extend our understanding of the RNase P cleavage site recognition process.
22.	Calmfors, Lars, et al. (författare) Dåliga jobbvillkor gör att Sverige tappar elitforskare 2014 Ingår i: Dagens nyheter. - : Bonnier. - 1101-2447. Tidskriftsartikel (populärvet., debatt m.m.)
23.	Crona, Mikael, et al. (författare) A Rare Combination of Ribonucleotide Reductases in the Social Amoeba Dictyostelium discoideum 2013 Ingår i: Journal of Biological Chemistry. - 0021-9258 .- 1083-351X. ; 288:12, s. 8198-8208 Tidskriftsartikel (refereegranskat)abstract Ribonucleotide reductases (RNRs) catalyze the only pathway for de novo synthesis of deoxyribonucleotides needed for DNA replication and repair. The vast majority of eukaryotes encodes only a class I RNR, but interestingly some eukaryotes, including the social amoeba Dictyostelium discoideum, encode both a class I and a class II RNR. The amino acid sequence of the D. discoideum class I RNR is similar to other eukaryotic RNRs, whereas that of its class II RNR is most similar to the monomeric class II RNRs found in Lactobacillus spp. and a few other bacteria. Here we report the first study of RNRs in a eukaryotic organism that encodes class I and class II RNRs. Both classes of RNR genes were expressed in D. discoideum cells, although the class I transcripts were more abundant and strongly enriched during mid-development compared with the class II transcript. The quaternary structure, allosteric regulation, and properties of the diiron-oxo/radical cofactor of D. discoideum class I RNR are similar to those of the mammalian RNRs. Inhibition of D. discoideum class I RNR by hydroxyurea resulted in a 90% reduction in spore formation and decreased the germination viability of the surviving spores by 75%. Class II RNR could not compensate for class I inhibition during development, and an excess of vitamin B12 coenzyme, which is essential for class II activity, did not improve spore formation. We suggest that class I is the principal RNR during D. discoideum development and growth and is important for spore formation, possibly by providing dNTPs for mitochondrial replication.
24.	Crona, Mikael, 1981-, et al. (författare) Assembly of a fragmented ribonucleotide reductase by protein interaction domains derived from a mobile genetic element 2011 Ingår i: Nucleic Acids Research. - : Oxford University Press. - 0305-1048 .- 1362-4962. ; 39:4, s. 1381-1389 Tidskriftsartikel (refereegranskat)abstract Ribonucleotide reductase (RNR) is a critical enzyme of nucleotide metabolism, synthesizing precursors for DNA replication and repair. In prokaryotic genomes, RNR genes are commonly targeted by mobile genetic elements, including free standing and intron-encoded homing endonucleases and inteins. Here, we describe a unique molecular solution to assemble a functional product from the RNR large subunit gene, nrdA that has been fragmented into two smaller genes by the insertion of mobE, a mobile endonuclease. We show that unique sequences that originated during the mobE insertion and that are present as C- and N-terminal tails on the split NrdA-a and NrdA-b polypeptides, are absolutely essential for enzymatic activity. Our data are consistent with the tails functioning as protein interaction domains to assemble the tetrameric (NrdA-a/NrdA-b)2 large subunit necessary for a functional RNR holoenzyme. The tails represent a solution distinct from RNA and protein splicing or programmed DNA rearrangements to restore function from a fragmented coding region and may represent a general mechanism to neutralize fragmentation of essential genes by mobile genetic elements.
25.	Crona, Mikael, et al. (författare) Biochemical Characterization of the Split Class II Ribonucleotide Reductase from Pseudomonas aeruginosa 2015 Ingår i: PLOS ONE. - : Public Library of Science (PLoS). - 1932-6203. ; 10:7 Tidskriftsartikel (refereegranskat)abstract The opportunistic pathogen Pseudomonas aeruginosa can grow under both aerobic and anaerobic conditions. Its flexibility with respect to oxygen load is reflected by the fact that its genome encodes all three existing classes of ribonucleotides reductase (RNR): the oxygen-dependent class I RNR, the oxygen-indifferent class II RNR, and the oxygen-sensitive class III RNR. The P. aeruginosa class II RNR is expressed as two separate polypeptides (NrdJa and NrdJb), a unique example of a split RNR enzyme in a free-living organism. A split class II RNR is also found in a few closely related gamma-Proteobacteria. We have characterized the P. aeruginosa class II RNR and show that both subunits are required for formation of a biologically functional enzyme that can sustain vitamin B12-dependent growth. Binding of the B12 coenzyme as well as substrate and allosteric effectors resides in the NrdJa subunit, whereas the NrdJb subunit mediates efficient reductive dithiol exchange during catalysis. A combination of activity assays and activity-independent methods like surface plasmon resonance and gas phase electrophoretic macromolecule analysis suggests that the enzymatically active form of the enzyme is a (NrdJa-NrdJb) 2 homodimer of heterodimers, and a combination of hydrogen-deuterium exchange experiments and molecular modeling suggests a plausible region in NrdJa that interacts with NrdJb. Our detailed characterization of the split NrdJ from P. aeruginosa provides insight into the biochemical function of a unique enzyme known to have central roles in biofilm formation and anaerobic growth.
26.	Crona, Mikael, 1981-, et al. (författare) NrdH-redoxin mediates high enzyme activity in manganese-reconstituted ribonucleotide reductase from Bacillus anthracis Annan publikation (övrigt vetenskapligt/konstnärligt)
27.	Crona, Mikael, et al. (författare) NrdH-Redoxin Protein Mediates High Enzyme Activity in Manganese-reconstituted Ribonucleotide Reductase from Bacillus anthracis 2011 Ingår i: Journal of Biological Chemistry. - Bethesda, Md. : American Society for Biochemistry and Molecular Biology. - 0021-9258 .- 1083-351X. ; 286:38, s. 33053-33060 Tidskriftsartikel (refereegranskat)abstract Bacillus anthracis is a severe mammalian pathogen encoding a class Ib ribonucleotide reductase (RNR). RNR is a universal enzyme that provides the four essential deoxyribonucleotides needed for DNA replication and repair. Almost all Bacillus spp. encode both class Ib and class III RNR operons, but the B. anthracis class III operon was reported to encode a pseudogene, and conceivably class Ib RNR is necessary for spore germination and proliferation of B. anthracis upon infection. The class Ib RNR operon in B. anthracis encodes genes for the catalytic NrdE protein, the tyrosyl radical metalloprotein NrdF, and the flavodoxin protein NrdI. The tyrosyl radical in NrdF is stabilized by an adjacent Mn(2)(III) site (Mn-NrdF) formed by the action of the NrdI protein or by a Fe(2)(III) site (Fe-NrdF) formed spontaneously from Fe(2+) and O(2). In this study, we show that the properties of B. anthracis Mn-NrdF and Fe-NrdF are in general similar for interaction with NrdE and NrdI. Intriguingly, the enzyme activity of Mn-NrdF was approximately an order of magnitude higher than that of Fe-NrdF in the presence of the class Ib-specific physiological reductant NrdH, strongly suggesting that the Mn-NrdF form is important in the life cycle of B. anthracis. Whether the Fe-NrdF form only exists in vitro or whether the NrdF protein in B. anthracis is a true cambialistic enzyme that can work with either manganese or iron remains to be established.
28.	Crona, Mikael, 1981- (författare) Quaternary structure and interaction approaches to allosteric regulation of class I ribonucleotide reductases 2010 Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract Deoxyribonucleic acid (DNA) chains in which our genetic blueprint is stored are built from four DNA precursors by DNA polymerases. The enzyme ribonucleotide reductase (RNR) provides the only de novo synthesis pathway of deoxyribonucleotides from ribonucleotides and is essential for nearly all organisms. All four ribonucleotides are substrates for RNR and key to this flexibility is a sophisticated allosteric regulation. Nucleotide effectors (ATP, dATP, dTTP or dGTP) binding to the allosteric specificity site determines substrate specificity for the active site. When present at high concentrations, dATP binds to the allosteric overall activity site and inhibits activity by an unknown mechanism. Three approaches, RNR activity measurements, subunit interaction studies and quaternary structure studies were applied to four different class I RNRs to address the allosteric overall regulation. We found that allosteric overall inhibition was closely linked to formation of tight and large RNR protein complexes; α4β4 complex for the Escherichia coli class Ia RNR and α6β2 for the Dictyostelium discoideum class Ia RNR with functional allosteric inhibitions. The Aeh1 phage class Ia RNR with a non-functional dATP inhibition showed weak remnant inhibition features, while the Bacillus anthracis class Ib RNR without the allosteric overall regulation domain lacked these features. In addition, we presented the first biochemical characterization of a mechanism to restore protein function after gene fragmentation, we showed that the B. anthracis class Ib RNR was most active when reconstituted with manganese and in the presence of a physiological redoxin protein and we found that the class Ia RNR is the principal RNR in D. discoideum, although the coexisting class II RNR could partly compensate class I RNR inhibition during axenic growth. Finally, our improved method for studying RNR interactions has potential for RNR inhibitor screening.
29.	Crona, Mikael, 1981-, et al. (författare) Subunit and small-molecule interaction of ribonucleotide reductases via surface plasmon resonance biosensor analyses 2010 Ingår i: Protein Engineering Design & Selection. - : Oxford University Press. - 1741-0126 .- 1741-0134. ; 23:8, s. 633-641 Tidskriftsartikel (refereegranskat)abstract Ribonucleotide reductase (RNR) synthesizes deoxyribonucleotides for DNA replication and repair and is controlled by sophisticated allosteric regulation involving differential affinity of nucleotides for regulatory sites. We have developed a robust and sensitive method for coupling biotinylated RNRs to surface plasmon resonance streptavidin biosensor chips via a 30.5 Å linker. In comprehensive studies on three RNRs effector nucleotides strengthened holoenzyme interactions, whereas substrate had no effect on subunit interactions. The RNRs differed in their response to the negative allosteric effector dATP that binds to an ATP-cone domain. A tight RNR complex was formed in Escherichia coli class Ia RNR with a functional ATP cone. No strengthening of subunit interactions was observed in the class Ib RNR from the human pathogen Bacillus anthracis that lacks the ATP cone. A moderate strengthening was seen in the atypical Aeromonas hydrophila phage 1 class Ia RNR that has a split catalytic subunit and a non-functional ATP cone with remnant dATP-mediated regulatory features. We also successfully immobilized a functional catalytic NrdA subunit of the E.coli enzyme, facilitating study of nucleotide interactions. Our surface plasmon resonance methodology has the potential to provide biological insight into nucleotide-mediated regulation of any RNR, and can be used for high-throughput screening of potential RNR inhibitors
30.	Crona, Mikael, 1981-, et al. (författare) The two classes of ribonucleotide reductase in the social amoeba Dictystelium discoideum Annan publikation (övrigt vetenskapligt/konstnärligt)
31.	Drottz-Sjöberg, Britt-Marie (författare) Perception of risk : studies of risk attitudes, perceptions and definitions 1991 Doktorsavhandling (övrigt vetenskapligt/konstnärligt)
32.	Drottz-Sjöberg, Britt-Marie (författare) Risk: conceptions, reactions and communication 1991 Ingår i: European Management Journal. - : Elsevier. - 0263-2373. ; 9:1, s. 88-97 Tidskriftsartikel (refereegranskat)abstract This paper presents a discussion of risks in modern society. They are becoming increasingly important in management and everyday life and communication problems are abundant. How are risks perceived? How do people react? How can communication be improved? Risks pertaining to people in general are usually seen as much larger than those for one's own person. The concept of risk is interpreted in different ways by different persons. Those who stress consequences tend to give higher risk ratings. Implications for risk communication and for the measurement of risk perception are discussed.
33.	Drottz-Sjöberg, Britt-Marie (författare) Risk perception and definitions of risk 1990 Annan publikation (övrigt vetenskapligt/konstnärligt)abstract The paper focuses on definitions of risk. Six studies were analyzed with respect to how non-expert subjects defined the concept of risk. In five of the studies subjects also rated risks of various adverse events with respect to personal risk, risk for people generally, and threat to society. Data from an additional study allowed a comparison between responses to a unidimensional scale measuring subjects' risk definitions and four suggested risk definitions. The results showed, firstly, that subjects rated risk significantly different when utilizing different perspectives. Thus personal risk was rated lower than risk to people in general, which in turn was rated lower than risk regarding the threat to society. Secondly, on the basis of two subsequent categorizations of the responses to the suggested risk definitions, the results showed that naive subjects did not usually employ a logically coherent definition of risk which exclusively involved the probability and consequence elements. Thirdly, subjects who could be accommodated within logical risk definition categories differed in their ratings on the basis of definition preference. Subjects who focused on a probability definition of risk gave lower risk ratings than those who used a risk definition which focused on consequences of an event. Fourthly, the comparison of a unidimensional rating scale and four separate definitions of risk indicated that the use of a unidimensional scale for measuring subjects' risk definitions may conceal a great variation of responses, especially with respect to the middle response alternative. The results are related to some diverging examples of how researchers define risk, and discussed in a framework where the different ratings emanating from the use of different perspectives are related to concern and behavior. It is suggested that differences between novices' and experts' risk assessments may, in part, be related to clarity, as well as type, of personal risk definition. Risk perception research concerned with low probability/high consequences events is finally related to research which also involves high probability/low consequences events, e.g. in marketing, and it is suggested that future risk perception research might benefit from considerations of both approaches.
34.	Due, Karin, 1953- (författare) Fysik, lärande samtal och genus. : En studie av gymnasieelevers gruppdiskussioner i fysik. 2009 Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract This thesis investigates how students in upper secondary school solve problems and discuss physics in small groups. The study examines how gender, knowledge in physics and the image of the subject physics are constructed in the students’ conversation and how these processes are related to each other. The theoretical framework includes a sociocultural perspective on learning and a gender perspective that views gender as both process and discourse and focus on how femininity and masculinity are constructed in social relations. 28 students in two classes at the science program participated in the study. 8 videotaped group discussions and 15 audiotaped interviews where analysed through thematic analysis and discourse analysis according to different research questions. The results show the complexity of a learning conversation. The character of the dialogue in the groups, the difficulties the student encounter when dealing with the tasks, and the social interaction in the groups, has a deep impact on the possibilities to develop the discussion about physics phenomena and concepts. The images of the subject physics and the images of a student skilled in physic that are constructed in the interviews are reconstructed in the students’ discussions and in their acting in the groups. But there are also inconsistencies and counter discourses. The possibilities for learning are related to the construction of gender and to equality issues within the groups. Traditional gendered positions are to a large extent reconstructed in the students’ interaction. Boys are for instance positioned as more competent in physics than girls. But traditional gendered positions are also resisted and challenged.
35.	Ekberg, Monica, et al. (författare) In vivo assay for low-activity mutant forms of Escherichia coli ribonucleotide reductase 2003 Ingår i: Journal of Bacteriology. - 0021-9193. ; 185:4, s. 1167-1173 Tidskriftsartikel (refereegranskat)
36.	Ekberg, Monika, et al. (författare) In vivo assay for low-activity mutant forms of Escherichia coli ribonucleotide reductase. 2003 Ingår i: J Bacteriol. - 0021-9193. ; 185:4, s. 1167-73 Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract Ribonucleotide reductase (RNR) catalyzes the essential production of deoxyribonucleotides in all living cells. In this study we have established a sensitive in vivo assay to study the activity of RNR in aerobic Escherichia coli cells. The method is based on the complementation of a chromosomally encoded nonfunctional RNR with plasmid-encoded RNR. This assay can be used to determine in vivo activity of RNR mutants with activities beyond the detection limits of traditional in vitro assays. E. coli RNR is composed of two homodimeric proteins, R1 and R2. The R2 protein contains a stable tyrosyl radical essential for the catalysis that takes place at the R1 active site. The three-dimensional structures of both proteins, phylogenetic studies, and site-directed mutagenesis experiments show that the radical is transferred from the R2 protein to the active site in the R1 protein via a radical transfer pathway composed of at least nine conserved amino acid residues. Using the new assay we determined the in vivo activity of mutants affecting the radical transfer pathway in RNR and identified some residual radical transfer activity in two mutant R2 constructs (D237N and W48Y) that had previously been classified as negative for enzyme activity. In addition, we show that the R2 mutant Y356W is completely inactive, in sharp contrast to what has previously been observed for the corresponding mutation in the mouse R2 enzyme.
37.	Friedrich, Nancy C, et al. (författare) Insertion of a homing endonuclease creates a genes-in-pieces ribonucleotide reductase that retains function 2007 Ingår i: PNAS. ; 104:15, s. 6176-6181 Tidskriftsartikel (refereegranskat)
38.	Grinberg, Inna, et al. (författare) Novel ATP-Cone-Driven Allosteric Regulation of Ribonucleotide Reductase Via the Radical-Generating Subunit 2018 Ingår i: Protein Science. - : Wiley-Blackwell. - 0961-8368 .- 1469-896X. ; 27, s. 87-88 Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)
39.	Gustafsson, Tomas N., et al. (författare) Bacillus anthracis Thioredoxin Systems, Characterization and Role as Electron Donors for Ribonucleotide Reductase 2012 Ingår i: Journal of Biological Chemistry. - 0021-9258 .- 1083-351X. ; 287:47 Tidskriftsartikel (refereegranskat)abstract Bacillus anthracis is the causative agent of anthrax, which is associated with a high mortality rate. Like several medically important bacteria, B. anthracis lacks glutathione but encodes many genes annotated as thioredoxins, thioredoxin reductases, and glutaredoxin-like proteins. We have cloned, expressed, and characterized three potential thioredoxins, two potential thioredoxin reductases, and three glutaredoxin-like proteins. Of these, thioredoxin 1 (Trx1) and NrdH reduced insulin, 5,5'-dithiobis-(2-nitrobenzoic acid) (DTNB), and the manganese-containing type Ib ribonucleotide reductase (RNR) from B. anthracis in the presence of NADPH and thioredoxin reductase 1 (TR1), whereas thioredoxin 2 (Trx2) could only reduce DTNB. Potential TR2 was verified as an FAD-containing protein reducible by dithiothreitol but not by NAD(P)H. The recently discovered monothiol bacillithiol did not work as a reductant for RNR, either directly or via any of the redoxins. The catalytic efficiency of Trx1 was 3 and 20 times higher than that of Trx2 and NrdH, respectively, as substrates for TR1. Additionally, the catalytic efficiency of Trx1 as an electron donor for RNR was 7-fold higher than that of NrdH. In extracts of B. anthracis, Trx1 was responsible for almost all of the disulfide reductase activity, whereas Western blots showed that the level of Trx1 was 15 and 60 times higher than that of Trx2 and NrdH, respectively. Our findings demonstrate that the most important general disulfide reductase system in B. anthracis is TR1/Trx1 and that Trx1 is the physiologically relevant electron donor for RNR. This information may provide a basis for the development of novel antimicrobial therapies targeting this severe pathogen.
40.	Hasan, Mahmudul, et al. (författare) Solution Structure of the dATP-Inactivated Class I Ribonucleotide Reductase From Leeuwenhoekiella blandensis by SAXS and Cryo-Electron Microscopy 2021 Ingår i: Frontiers in Molecular Biosciences. - : Frontiers Media SA. - 2296-889X. ; 8 Tidskriftsartikel (refereegranskat)abstract The essential enzyme ribonucleotide reductase (RNR) is highly regulated both at the level of overall activity and substrate specificity. Studies of class I, aerobic RNRs have shown that overall activity is downregulated by the binding of dATP to a small domain known as the ATP-cone often found at the N-terminus of RNR subunits, causing oligomerization that prevents formation of a necessary alpha(2)beta(2) complex between the catalytic (alpha(2)) and radical generating (beta(2)) subunits. In some relatively rare organisms with RNRs of the subclass NrdAi, the ATP-cone is found at the N-terminus of the beta subunit rather than more commonly the alpha subunit. Binding of dATP to the ATP-cone in beta results in formation of an unusual beta(4) tetramer. However, the structural basis for how the formation of the active complex is hindered by such oligomerization has not been studied. Here we analyse the low-resolution three-dimensional structures of the separate subunits of an RNR from subclass NrdAi, as well as the alpha(4)beta(4) octamer that forms in the presence of dATP. The results reveal a type of oligomer not previously seen for any class of RNR and suggest a mechanism for how binding of dATP to the ATP-cone switches off catalysis by sterically preventing formation of the asymmetrical alpha(2)beta(2) complex.
41.	Hoeppner, Marc Patrick, 1980- (författare) The deep evolutionary roots of non-coding RNA - a comparative genomics approach 2011 Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract Non-coding RNAs (ncRNA) are a diverse group of genes that do not encode proteins but function exclusively on the level of RNA and were originally suggested to be remnants of a pre-DNA stage of life known as the RNA world. More recent work, however, has uncovered a rich repertoire of previously unknown families with possible consequences for our understanding of the origin and evolution of the modern RNA infrastructure. The main goal of this thesis was therefore to re-examine the evolutionary history of RNAs and theories regarding the transition from an RNA world in light of recent advances in molecular and computational biology. Using comparative genomics approaches and sequence data from all domains of life, my work shows that the majority of known RNAs exhibit a highly domain-specific distribution, compatible with an ongoing emergence rather than deep ancestry. Focusing on small nucleolar RNAs (snoRNA), I find that the eukaryote ancestor possessed a complex snoRNA infrastructure, but that intronic snoRNAs are mobile over larger evolutionary time scales. The latter has consequences for predictions made by the Introns-first hypothesis, a framework to explain the emergence of introns in an RNA world and which we revisited in light of advances in our understanding of the evolutionary dynamics of introns. A more in-depth analysis of ncRNA mobility across vertebrates found intronic copies of both snoRNAs and miRNAs to be more stable than intergenic ones, suggesting that this arrangement may be a consequence of co-expression. Also, snoRNAs are frequently located in highly expressed genes, in line with their role in ribosome biogenesis. Finally, a closer examination of the genomic distribution of two essential ncRNAs, snoRNA U3 and the spliceosomal RNA U1 shows that both are present in numerous copies across vertebrate genomes. Using next-generation sequencing data, I tested whether this is the result of genetic drift or a requirement for having many copies.
42.	Hofer, Anders, et al. (författare) DNA building blocks : keeping control of manufacture 2012 Ingår i: Critical reviews in biochemistry and molecular biology. - London : Informa UK Limited. - 1040-9238 .- 1549-7798. ; 47:1, s. 50-63 Forskningsöversikt (refereegranskat)abstract Ribonucleotide reductase (RNR) is the only source for de novo production of the four deoxyribonucleoside triphosphate (dNTP) building blocks needed for DNA synthesis and repair. It is crucial that these dNTP pools are carefully balanced, since mutation rates increase when dNTP levels are either unbalanced or elevated. RNR is the major player in this homeostasis, and with its four different substrates, four different allosteric effectors and two different effector binding sites, it has one of the most sophisticated allosteric regulations known today. In the past few years, the structures of RNRs from several bacteria, yeast and man have been determined in the presence of allosteric effectors and substrates, revealing new information about the mechanisms behind the allosteric regulation. A common theme for all studied RNRs is a flexible loop that mediates modulatory effects from the allosteric specificity site (s-site) to the catalytic site for discrimination between the four substrates. Much less is known about the allosteric activity site (a-site), which functions as an on-off switch for the enzyme's overall activity by binding ATP (activator) or dATP (inhibitor). The two nucleotides induce formation of different enzyme oligomers, and a recent structure of a dATP-inhibited α(6)β(2) complex from yeast suggested how its subunits interacted non-productively. Interestingly, the oligomers formed and the details of their allosteric regulation differ between eukaryotes and Escherichia coli. Nevertheless, these differences serve a common purpose in an essential enzyme whose allosteric regulation might date back to the era when the molecular mechanisms behind the central dogma evolved.
43.	Högbom, Martin, et al. (författare) Crystal structure of the di-iron/radical protein of ribonucleotide reductase from Corynebacterium ammoniagenes. 2002 Ingår i: Biochemistry. - 0006-2960. ; 41:4, s. 1381-9 Tidskriftsartikel (refereegranskat)abstract Ribonucleotide reductase (RNR) is the enzyme performing de novo production of the four deoxyribonucleotides needed for DNA synthesis. All mammals as well as some prokaryotes express the class I enzyme which is an alpha(2)beta(2) protein. The smaller of the homodimers, denoted R2, contains a di-iron carboxylate site which, upon reaction with molecular oxygen, generates a stable tyrosyl radical needed for catalysis. The three-dimensional structure of the oxidized class Ib RNR R2 from Corynebacterium ammoniagenes has been determined at 1.85 A resolution and refined to an R-value of 15.8% (R(free) = 21.3%). In addition, structures of both the reduced iron-containing, and manganese-substituted protein have been solved. The C. ammoniagenes R2 has been proposed to be manganese-dependent. The present structure provides evidence that manganese is not oxidized by the protein, in agreement with recent biochemical data, and that no obvious structural abnormalities are seen in the oxidized and reduced iron-containing forms, giving further support that the protein is indeed an iron-dependent RNR R2. The di-manganese structure also provides an explanation for the magnetic properties of this site. The structure of the oxidized C. ammoniagenes R2 also reveals an additional water molecule bridging the radical and the iron site, which has not previously been seen in any other R2 structure and which might have important mechanistic implications.
44.	Johansson, Renzo, et al. (författare) High-resolution crystal structures of the flavoprotein NrdI in oxidized and reduced states – an unusual flavodoxin 2010 Ingår i: The FEBS Journal. - : Wiley. - 1742-464X .- 1742-4658. ; 277:20, s. 4265-4277 Tidskriftsartikel (refereegranskat)abstract The small flavoprotein NrdI is an essential component of the class Ib ribonucleotide reductase system in many bacteria. NrdI interacts with the class Ib radical generating protein NrdF. It is suggested to be involved in the rescue of inactivated diferric centres or generation of active dimanganese centres in NrdF. Although NrdI bears a superficial resemblance to flavodoxin, its redox properties have been demonstrated to be strikingly different. In particular, NrdI is capable of two-electron reduction, whereas flavodoxins are exclusively one-electron reductants. This has been suggested to depend on a lesser destabilization of the negatively-charged hydroquinone state than in flavodoxins. We have determined the crystal structures of NrdI from Bacillus anthracis, the causative agent of anthrax, in the oxidized and semiquinone forms, at resolutions of 0.96 and 1.4 Å, respectively. These structures, coupled with analysis of all curated NrdI sequences, suggest that NrdI defines a new structural family within the flavodoxin superfamily. The conformational behaviour of NrdI in response to FMN reduction is very similar to that of flavodoxins, involving a peptide flip in a loop near the N5 atom of the flavin ring. However, NrdI is much less negatively charged than flavodoxins, which is expected to affect its redox properties significantly. Indeed, sequence analysis shows a remarkable spread in the predicted isoelectric points of NrdIs, from approximately pH 4–10. The implications of these observations for class Ib ribonucleotide reductase function are discussed.
45.	Johansson, Renzo, et al. (författare) Structural Mechanism of Allosteric Activity Regulation in a Ribonucleotide Reductase with Double ATP Cones 2016 Ingår i: Structure. - : Elsevier BV. - 0969-2126 .- 1878-4186. ; 24:6, s. 906-917 Tidskriftsartikel (refereegranskat)abstract Ribonucleotide reductases (RNRs) reduce ribonucleotides to deoxyribonucleotides. Their overall activity is stimulated by ATP and downregulated by dATP via a genetically mobile ATP cone domain mediating the formation of oligomeric complexes with varying quaternary structures. The crystal structure and solution X-ray scattering data of a novel dATP-induced homotetramer of the Pseudomonas aeruginosa class I RNR reveal the structural bases for its unique properties, namely one ATP cone that binds two dATP molecules and a second one that is non-functional, binding no nucleotides. Mutations in the observed tetramer interface ablate oligomerization and dATP-induced inhibition but not the ability to bind dATP. Sequence analysis shows that the novel type of ATP cone may be widespread in RNRs. The present study supports a scenario in which diverse mechanisms for allosteric activity regulation are gained and lost through acquisition and evolutionary erosion of different types of ATP cone.
46.	Johansson, Unn-Britt, et al. (författare) Mixed methods study on the feasibility of implementing periodic continuous glucose monitoring among individuals with type 2 diabetes mellitus in a primary care setting 2024 Ingår i: Heliyon. - 2405-8440. ; 10:8 Tidskriftsartikel (refereegranskat)abstract BACKGROUND: Health care professionals (HCPs) play a central role in leveraging technologies to support individuals with diabetes. This mixed-method study was completed to determine the feasibility of implementing periodic continuous glucose monitoring (CGM) in a primary care setting.AIM: This study aimed to evaluate and describe the experiences of using periodic CGM with data visualization tools in patients with type 2 diabetes to foster a person-centered approach in a primary care setting.METHODS: Fifty outpatients aged ≥18 years, diagnosed with type 2 diabetes, and with a disease duration of at least 2 years were included in this study. Data were collected from April 2021 to January 2022. Patients completed a single period of sensor measurements for 28 days and a diabetes questionnaire about feelings and experiences of health care. HbA1c was also measured. A focus group interview was conducted to evaluate and describe the HCPs experiences of using periodic CGM.RESULTS: Patients reported to HCPs that the CGM device was comfortable to wear and noted that LibreView was easy to use when scanning the sensor to obtain and visualize the glucose levels and trends. Data availability of CGM data was >70 %.Clinical observations revealed a mean reduction in HbA1c, mmol/mol from 60.06 [7.65 %] at baseline to 55.42 [7.20 %] after 4 weeks (p < 0.001). Two categories were identified: 1) Fostering dialogue on self-care and 2) Promoting understanding.CONCLUSIONS: The HCPs and participants in this study had a positive experience or viewed the implementation of periodic CGM with data visualization tools as a positive experience and appeared to be feasible for implementation in a primary care setting.
47.	Jonna, Venkateswara Rao, et al. (författare) Diversity in Overall Activity Regulation of Ribonucleotide Reductase 2015 Ingår i: Journal of Biological Chemistry. - 0021-9258 .- 1083-351X. ; , s. 1-24 Tidskriftsartikel (refereegranskat)abstract Ribonucleotide reductase (RNR) catalyzes the reduction of ribonucleotides to the corresponding deoxyribonucleotides, which are used as building blocks for DNA replication and repair. This process is tightly regulated via two allosteric sites, the specificity site (s-site) and the overall activity site (a-site). The a-site resides in an N-terminal ATP cone domain that binds dATP or ATP and functions as an on/off switch, whereas the composite s-site binds ATP, dATP, dTTP, or dGTP and determines which substrate to reduce. There are three classes of RNRs, and class I RNRs consist of different combinations of α and β subunits. In eukaryotic and Escherichia coli canonical class I RNRs, dATP inhibits enzyme activity through the formation of inactive α6 and α4β4 complexes, respectively. Here we show that the Pseudomonas aeruginosa class I RNR has a duplicated ATP cone domain and represents a third mechanism of overall activity regulation. Each α polypeptide binds three dATP molecules, and the N-terminal ATP cone is critical for binding two of the dATPs because a truncated protein lacking this cone could only bind one dATP to its s-site. ATP activates the enzyme solely by preventing dATP from binding. The dATP-induced inactive form is an α4 complex, which can interact with β2 to form a non-productive α4β2 complex. Other allosteric effectors induce a mixture of α2 and α4 forms, with the former being able to interact with β2 to form active α2β2 complexes. The unique features of the P. aeruginosa RNR are interesting both from evolutionary and drug discovery perspectives.
48.	Kasrayan, Alex, et al. (författare) Enhancement by effectors and substrate nucleotides of R1-R2 interactions in Escherichia coli class Ia ribonucleotide reductase 2004 Ingår i: Journal of Biological chemistry. - 0021-9258. ; 279:30, s. 31050-31057 Tidskriftsartikel (refereegranskat)
49.	Kasrayan, Alex, et al. (författare) Enhancement by effectors and substrate nucleotides of R1-R2 interactions in Escherichia coli class Ia ribonucleotide reductase. 2004 Ingår i: J Biol Chem. - 0021-9258. ; 279:30, s. 31050-7 Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract Ribonucleotide reductases are a family of essential enzymes that catalyze the reduction of ribonucleotides to their corresponding deoxyribonucleotides and provide cells with precursors for DNA synthesis. The different classes of ribonucleotide reductase are distinguished based on quaternary structures and enzyme activation mechanisms, but the components harboring the active site region in each class are evolutionarily related. With a few exceptions, ribonucleotide reductases are allosterically regulated by nucleoside triphosphates (ATP and dNTPs). We have used the surface plasmon resonance technique to study how allosteric effects govern the strength of quaternary interactions in the class Ia ribonucleotide reductase from Escherichia coli, which like all class I enzymes has a tetrameric alpha(2) beta(2) structure. The component alpha(2)called R1 harbors the active site and two types of binding sites for allosteric effector nucleotides, whereas the beta(2) component called R2 harbors the tyrosyl radical necessary for catalysis. Our results show that only the known allosteric effector nucleotides, but not non-interacting nucleotides, promote a specific interaction between R1 and R2. Interestingly, the presence of substrate together with allosteric effector nucleotide strengthens the complex 2-3 times with a similar free energy change as the mutual allosteric effects of substrate and effector nucleotide binding to protein R1 in solution experiments. The dual allosteric effects of dATP as positive allosteric effector at low concentrations and as negative allosteric effector at high concentrations coincided with an almost 100-fold stronger R1-R2 interaction. Based on the experimental setup, we propose that the inhibition of enzyme activity in the E. coli class Ia enzyme occurs in a tight 1:1 complex of R1 and R2. Most intriguingly, we also discovered that thioredoxin, one of the physiological reductants of ribonucleotide reductases, enhances the R1-R2 interaction 4-fold.
50.	Kasrayan, Alex, 1973- (författare) Reaction Mechanism and Allosteric Regulation of Class Ia Ribonucleotide Reductase from Escherichia coli 2004 Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract Ribonculeotide reductase (RNR) plays a key role in catalysing a reaction that provides all living organisms with building blocks for DNA. The RNR enzyme catalyses the conversion of ribonucleotides to their corresponding deoxyribonucleotides, by using free radical chemistry. The class Ia enzyme from Escherichia coli is composed of two components, R1 and R2 proteins. Both components are required for the catalytic reaction. The R2 protein contains a stable tyrosyl free radical, which is directly involved in the catalysis. The R1 protein, contains the active site and two different allosteric sites, which are responsible for regulating the enzyme activity and its substrate specificity.An evolutionary conserved active site residue, Asn437, was studied. Employing site directed mutagensis it was shown that the Asn437 is essential for the catalytic reaction. Also using biophysical methods, it was shown that the Asn437 residue participates in the later part of the catalytic reaction.By using protein engineering, two conserved overall activity residues His59 and His88 were shown to be involved in the allosteric regulation of enzymatic activity. Furthermore, it was shown by biosensor technique (BIAcore) that the His59 and His88 participate in a communication network that regulates the binding affinity between the R1 and R2 components in response to the presence of certain allosteric effectors.The influence of the allosteric effectors and substrate nucleotides on the wild type R1/R2 interaction was investigated using biosensor technique. The presence of allosteric effectors strengthened the affinity between the components R1 and R2 as compared to the affinity in the absence of effectors. Interestingly, when both allosteric effectors and substrate nucleotides were present, the affinity between the R1 and R2 components was noticeably stronger as compared to the situations where only the allosteric effector was present.Finally, the residues located in the interaction area of the dimeric R1 protein from E. coli were studied. The aim was to understand their importance for the formation of the active dimeric form of R1. Interestingly, slight alterations of the chemical properties of single side chains resulted in drastic changes in dimer stability, indicating the importance of their interaction ability for dimer formation.

Skapa referenser, mejla, bekava och länka

Länka till träfflistan

Träfflista för sökning "WFRF:(Sjöberg Britt Marie) "

Avgränsa träffmängd

År