| 1. |
- Georgieva, Polina, et al.
(författare)
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The reaction mechanism of phenylethanolamine N-methyltransferase : A density functional theory study
- 2009
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Ingår i: Biochimica et Biophysica Acta - Proteins and Proteomics. - : Elsevier BV. - 1570-9639 .- 1878-1454. ; 1794:12, s. 1831-1837
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Tidskriftsartikel (refereegranskat)abstract
- Hybrid density functional theory methods were used to investigate the reaction mechanism of human phenylethanolamine N-methyltransferase (hPNMT). This enzyme catalyzes the S-adenosyl-L-methionine-dependent conversion of norepinephrine to epinephrine, which constitutes the terminal step in the catecholamine biosynthesis. Several models of the active site were constructed based on the X-ray structure. Geometries of the stationary points along the reaction path were optimized and the reaction barrier and energy were calculated and compared to the experimental values. The calculations demonstrate that the reaction takes place via an S(N)2 mechanism with methyl transfer being rate-limiting, a suggestion supported by mutagenesis studies. Optimal agreement with experimental data is reached using a model in which both active site glutamates; are protonated. Overall, the mechanism of hPNMT is more similar to those of catechol O-methyltransferase and glycine N-methyltransferase than to that of guanidinoacetate N-methyltransferase in which methyl transfer is coupled to proton transfer.
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| 2. |
- Elfström, Lisa, et al.
(författare)
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The Saccharomyces cerevisiae ORF YNR064c protein has characteristics of an 'orphaned' epoxide hydrolase
- 2005
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Ingår i: Biochimica et Biophysica Acta - Proteins and Proteomics. - : Elsevier BV. - 1570-9639 .- 1878-1454. ; 1748, s. 213-221
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Tidskriftsartikel (refereegranskat)abstract
- The open reading frame YNR064c in Saccharomyces cerevisiae encodes a protein tentatively assigned as similar to a bacterialdehalogenase. In this study we conclude that the YNR064c protein displays characteristics of an epoxide hydrolase belonging to the a/hhydrolasefold family of enzymes. Endogenous expression of the protein in S. cerevisiae was confirmed and a His-tagged variant of theprotein was heterologously expressed in both Escherichia coli and Pichia pastoris for isolation and characterization. The YNR064c proteindisplayed low but reproducible epoxide hydrolase activity with racemic phenanthrene 9,10-oxide and trans- or cis-stilbene oxide.Phylogenetic analysis of related gene products found in various microorganisms suggested that the YNR064c protein is a member of a newsubclass of a/h-hydrolase fold enzymes.
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| 3. |
- Enroth, Cristofer, et al.
(författare)
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Crystal structure of a protein, structurally related to glycosyltransferases, encoded in the Rhodobacter blasticus atp operon
- 2008
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Ingår i: Biochimica et Biophysica Acta - Proteins and Proteomics. - Amsterdam : Elsevier/North Holland. - 1570-9639 .- 1878-1454. ; 1784:2, s. 379-384
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Tidskriftsartikel (refereegranskat)abstract
- The F1-ATP synthase atp operon in the proteobacterium Rhodobacter blasticus contains six open reading frames, encoding six hypothetical proteins. Five of these subunits, in the stoichiometry (ab)3gde make up the catalytic F1-ATP synthase complex similarly in bacteria, chloroplasts and mitochondria. The sixth gene of the Rb. blasticus atp operon, urf6, shows very little sequence homology to any protein of known structure or function. The gene has previously been cloned, the product (called majastridin) has been heterologously expressed in Escherichia coli, and purified to high homogeneity (Brosché et al. (1998) Eur. J. Biochem. 255: 87-92). We have solved the X-ray crystal structure and refined a model of majastridin to atomic resolution. Here we present the crystal structures of apo-majastridin and the complex of majastridin with Mn2+ and UDP and show it has extensive structural similarity to glycosyltransferases (EC 2.4). This is the first structure determined from a new group of distantly related bacterial proteins of at least six members. They share the identical amino acids that bind Mn2+and a triplet of amino acids in the putative sugar-binding site.
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| 4. |
- Graber, Marianne, et al.
(författare)
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Solvent as a competitive inhibitor for Candida antarctica lipase B
- 2007
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Ingår i: Biochimica et Biophysica Acta - Proteins and Proteomics. - : Elsevier BV. - 1570-9639 .- 1878-1454. ; 1774:8, s. 1052-1057
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Tidskriftsartikel (refereegranskat)abstract
- In enzyme-catalyzed reactions, the choice of solvent often has a marked effect on the reaction outcome. In this paper, it is shown that solvent effects could be explained by the ability of the solvent to act as a competitive inhibitor to the substrate. Experimentally, the effect of six solvents, 2-pentanone, 3-pentanone, 2-methyl-2-pentanol, 3-methyl-3-pentanot, 2-methylpentane and 3-methylpentane, was studied in a solid/gas reactor. As a model reaction, the CALB-catalyzed transacylation between methyl propanoate and I -propanol, was studied. It was shown that both ketones inhibited the enzyme activity whereas the tertiary alcohols and the hydrocarbons did not. Alcohol inhibition constants, K-il were changed to "K-i", determined in presence of 2-pentanone, 3-pentanone, and 3-methyl-3-pentanol, confirmed the marked inhibitory character of the ketones and an absence of inhibition of 3-methyl-3-pentanol. The molecular modeling study was performed on three solvents, 2-pentanone, 2-methyl-2-pentanol and 2-methyl pentane. It showed a clear inhibitory effect for the ketone and the tertiary alcohol, but no effect for the hydrocarbon. No change in enzyme conformation was seen during the simulations. The study led to the conclusion that the effect of added organic component on lipase catalyzed transacylation could be explained by the competitive inhibitory character of solvents towards the first binding substrate methyl propanoate.
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| 5. |
- Lindås, Ann-Christin, et al.
(författare)
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Investigation of a role for Glu-331 and Glu-305 in substrate binding of tripeptidyl-peptidase II
- 2008
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Ingår i: Biochimica et Biophysica Acta - Proteins and Proteomics. - : Elsevier BV. - 1570-9639 .- 1878-1454. ; 1784:12, s. 1899-1907
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Tidskriftsartikel (refereegranskat)abstract
- The aim of this study was to investigate the mechanism by which tripeptidyl-peptidase II (TPP II) can specifically release tripeptides from the free N-terminus of an oligopeptide. The subtilisin-like N-terminal part of TPP II was modelled using subtilisin as template. Two glutamate residues (Glu-305 and Glu-331) appeared to be positioned so as to interact with the positively charged N-terminus of the substrate. In order to test this potential interaction, both residues were replaced by glutamine and lysine. The catalytic efficiency was reduced 400-fold for the E331Q variant and 20000-fold for the E331K variant, compared with the wild-type (wt). A substantial part of this reduction was due to decreased substrate affinity, since the K(M) for both mutants was at least two orders of magnitude greater than for the wt. This decrease was linked specifically to interaction with the free N-terminal amino group, based on inhibition studies. Glu-305 appears to be essential for enzymatic activity, but the extremely low activity of the E305Q variant prevented an investigation of the involvement of Glu-305 in substrate binding. The present work is, to our knowledge, the first report to investigate a mechanism for a tripeptidyl-peptidase activity through site-directed mutagenesis.
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| 6. |
- Meng, Meng, et al.
(författare)
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Domain-specific determinants of catalysis/ substrate binding and the oligomerization status of barley UDP-glucose pyrophosphorylase
- 2009
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Ingår i: Biochimica et Biophysica Acta - Proteins and Proteomics. - : Elsevier BV. - 1570-9639 .- 1878-1454. ; 1794, s. 1734-1742
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Tidskriftsartikel (refereegranskat)abstract
- UDP-glucose (UDPG) pyrophosphorylase (UGPase) produces UDPG for sucrose and polysaccharide synthesis and glycosylation reactions. In this study, several barley UGPase mutants were produced, either single amino acid mutants or involving deletions of N- and C-terminal domains (Ncut and Ccut mutants, respectively) and of active site region ("NB loop"). The Del-NB mutant yielded no activity, whereas Ncut deletions and most of Ccut mutants, including short deletions at the so called "I-loop" region of C-terminal domain, as well as a single K260A mutant resulted in very low activity. For wt and the mutants, kinetics with UDPG were linear on reciprocal plots, whereas PPi at concentrations above 1mM exerted strong substrate inhibition. Both K260A and most of the Ccut mutants had very high K(m) with PPi (up to 33mM), whereas Ncut deletions had greatly increased K(m) with UDPG (up to 57mM). Surprisingly, an 8 amino acid deletion from end of the C-terminus resulted in an enzyme (Ccut-8 mutant) with 44% higher activity when compared to wt, but with similar K(m) values. Whereas Ccut-8 existed solely as a monomer, other deletion mutants had a more oligomerized status, e.g. Ncut mutants existing primarily as dimers. Overall, the data confirmed the essential role of NB loop in catalysis, but also pointed out to the role of both N- and C-termini for activity, substrate binding and oligomerization. The importance of oligomerization status for enzymatic activity of UGPase is discussed.
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| 7. |
- Meng, Meng, et al.
(författare)
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Molecular and kinetic characterization of two UDP-glucose pyrophosphorylases, products of distinct genes, from Arabidopsis
- 2008
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Ingår i: Biochimica et Biophysica Acta - Proteins and Proteomics. - : Elsevier. - 1570-9639 .- 1878-1454. ; 1784:6, s. 967-972
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Tidskriftsartikel (refereegranskat)abstract
- UDP-glucose pyrophosphorylase (UGPase) is an important enzyme in the production (and conversions) of UDP-glucose, a key precursor for carbohydrate biosynthesis. cDNAs corresponding to two UGPase isozymes in Arabidopsis were overexpressed in Escherichia coli and, subsequently, the recombinant proteins were purified and characterized. Both proteins were highly conserved, sharing 93% identity. Based on crystal structure-derived images, the main amino acid differences mapped to N- and C-termini domains, but not to central active site region. The two proteins existed mainly as monomers, and they had similar molecular masses of ca. 53 kDa. However, comparison of molecular masses of UGPases from Arabidopsis root and leaf extracts revealed that the root protein was slightly larger, suggesting a post-translational modification. Specific activity of the purified UGPase-1 was ca. 10–30% lower than that of UGPase-2, depending on direction of the reaction, whereas its Km values with all substrates in both directions of the reaction were consistently ca. twice lower than those of UGPase-2 (0.03–0.14 mM vs. 0.07–0.36 mM, respectively). Both proteins were “true” UGPases, and had no activity with ADP-glucose/ATP or galactose-1-P. Equilibrium constant for both proteins was ca. 0.3, suggesting preference for the pyrophosphorolysis direction of the reaction. The data are discussed with respect to potential roles of UGPase in carbohydrate synthesis/metabolism in Arabidopsis.
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| 8. |
- Okamoto, H., et al.
(författare)
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Mutation analysis of the human 5-lipoxygenase C-terminus : Support for a stabilizing C-terminal loop
- 2005
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Ingår i: Biochimica et Biophysica Acta - Proteins and Proteomics. - : Elsevier BV. - 1570-9639 .- 1878-1454. ; 1749:1, s. 123-131
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Tidskriftsartikel (refereegranskat)abstract
- Lipoxygenases contain prosthetic iron, in human 5-lipoxygenase (5LO) the C-terminal isoleucine carboxylate constitutes one of five identified ligands. ATP is one of several factors determining 5LO activity. We compared properties of a series of 5LO C-terminal deletion mutants (one to six amino acid residues deleted). All mutants were enzymatically inactive (expected due to loss of iron), but expression yield (in E. coli) and affinity to ATP-agarose was markedly different. Deletion of up to four C-terminal residues was compatible with good expression and retained affinity to the ATP-column, as for wild-type 5LO. However when also the fifth residue was deleted (Asn-669) expression yield decreased and the affinity to ATP was markedly diminished. This was interpreted as a result of deranged structure and stability, due to loss of a hydrogen bond between Asn-669 and His-399. Mutagenesis of these residues supported this conclusion. In the structure of soybean lipoxygenase-1, a C-terminal loop was pointed out as important for correct orientation of the C-terminus. Accordingly, a hydrogen bond appears to stabilize such a C-terminal loop also in 5LO. © 2005 Elsevier B.V. All rights reserved.
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| 9. |
- Stenvall, Maria, et al.
(författare)
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High-throughput solubility assay for purified recombinant protein immunogens
- 2005
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Ingår i: Biochimica et Biophysica Acta - Proteins and Proteomics. - : Elsevier BV. - 1570-9639 .- 1878-1454. ; 1752:1, s. 6-10
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Tidskriftsartikel (refereegranskat)abstract
- A high-throughput assay is described for analysis of the solubility of purified recombinant proteins. The assay is based on affinity purification of proteins in the presence of chaotropic agents followed by a dilution and incubation step to investigate the solubility in the absence of high concentrations of such agents. The assay can be performed in a 96-well format, which makes it well suited for high-throughput applications. For 125 recombinant proteins expressed as part of an antibody-based proteomics effort, experimental solubility data were compared to calculated hydrophobicity values based on the amino acid sequence of each protein. This comparison showed only weak correlation between the theoretical and experimental values, which emphasizes the importance of experimental assays to determine the solubility of recombinant proteins.
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| 10. |
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