| 1. |
- Davidsson, Jan, et al.
(författare)
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Structural determination of a transient isomer of CH2I2 by picosecond x-ray diffraction
- 2005
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Ingår i: Physical Review Letters. - 0031-9007 .- 1079-7114. ; 94:24
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Tidskriftsartikel (refereegranskat)abstract
- Ultrafast time-resolved spectroscopic studies of complex chemical reactions in solution are frequently hindered by difficulties in recovering accurate structural models for transient photochemical species. Time-resolved x-ray and electron diffraction have recently emerged as techniques for probing the structural dynamics of short lived photointermediates. Here we determine the structure of a transient isomer of photoexcited CH2I2 in solution and observe the downstream reactions of the initial photoproducts. Our results illustrate how geminate recombination proceeds via the formation of a transient covalent bond onto the iodine atom remaining with the parent molecule. Further intramolecular rearrangements are thus required for the CH2I-I isomer to return to CH2I2. The generation of I-3(-) from those iodine radicals escaping the solvent cage is also followed with time.
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| 2. |
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| 3. |
- Jacobson, Frida, 1975, et al.
(författare)
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High resolution X-ray structures of the oxidised and reduced forms of nitrite reductase from Rhodobacter sphaeroides 2.4.3
- 2005
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Ingår i: Acta Crystallography D. - 0907-4449 .- 1399-0047. ; 61, s. 1190-1198
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Tidskriftsartikel (refereegranskat)abstract
- Nitrite reductase is an enzyme operating in the denitrification pathway which catalyses the conversion of nitrite (NO2(-)) to gaseous nitric oxide (NO). Here, crystal structures of the oxidized and reduced forms of the copper-containing nitrite reductase from Rhodobacter sphaeroides 2.4.3 are presented at 1.74 and 1.85 A resolution, respectively. Whereas the structure of the enzyme is very similar to those of other copper-containing nitrite reductases, folding as a trimer and containing two copper sites per monomer, the structures reported here enable conformational differences between the oxidized and reduced forms of the enzyme to be identified. In the type 1 copper site, a rotational perturbation of the side chain of the copper ligand Met182 occurs upon reduction. At the type 2 copper site, a dual conformation of the catalytic residue His287 is observed in the oxidized structure but is lacking in the reduced structure, such that the interactions of the oxidized type 2 copper ion can be regarded as adopting octahedral geometry. These findings shed light on the structural mechanism of the reduction of a copper-bound nitrite to nitric oxide and water.
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| 4. |
- Jacobson, Frida, 1975, et al.
(författare)
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pH dependence of copper geometry, reduction potential, and nitrite affinity in nitrite reductase
- 2007
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Ingår i: Journal of Biological Chemistry. - 0021-9258 .- 1083-351X. ; 282:9, s. 6347-6355
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Tidskriftsartikel (refereegranskat)abstract
- Many properties of copper-containing nitrite reductase are pH-dependent, such as gene expression, enzyme activity, and substrate affinity. Here we use x-ray diffraction to investigate the structural basis for the pH dependence of activity and nitrite affinity by examining the type 2 copper site and its immediate surroundings in nitrite reductase from Rhodobacter sphaeroides 2.4.3. At active pH the geometry of the substrate-free oxidized type 2 copper site shows a near perfect tetrahedral geometry as defined by the positions of its ligands. At higher pH values the most favorable copper site geometry is altered toward a more distorted tetrahedral geometry whereby the solvent ligand adopts a position opposite to that of the His-131 ligand. This pH-dependent variation in type 2 copper site geometry is discussed in light of recent computational results. When co-crystallized with substrate, nitrite is seen to bind in a bidentate fashion with its two oxygen atoms ligating the type 2 copper, overlapping with the positions occupied by the solvent ligand in the high and low pH structures. Fourier transformation infrared spectroscopy is used to assign the pH dependence of the binding of nitrite to the active site, and EPR spectroscopy is used to characterize the pH dependence of the reduction potential of the type 2 copper site. Taken together, these spectroscopic and structural observations help to explain the pH dependence of nitrite reductase, highlighting the subtle relationship between copper site geometry, nitrite affinity, and enzyme activity.
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| 5. |
- Jacobson, Frida, 1975
(författare)
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Structural and biochemical analysis of two copper proteins - plastocyanin from spinach and nitrite reductase from Rhodobacter sphaeroides 2.4.3
- 2006
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Plastocyanin from spinach and nitrite reductase from Rhodobacter sphaeroides 2.4.3 are two copper-containing proteins that are involved in biological electron transport chains: plastocyanin operates in photosynthesis and nitrite reductase takes part in the denitrification pathway. X-ray crystallography together with biochemical analysis of both macromolecules has provided us with new insight into the chemical details of their biological mechanisms. Mutational studies of plastocyanin were performed to elucidate the importance of a hydrophobic patch for electron transfer activity. In addition, investigation of the thermostability of plastocyanin by the insertion of a disulfide bond indicated an increased stability of the type 1 Cu site in one mutant and resulted in changes in crystallisation properties of the protein. The crystal structures of the reduced and oxidised species of nitrite reductase were solved and compared with regard to Cu site environment. Further crystallographic work includes structures of nitrite reductase at pH 8.4 and pH 6.0 and with or without nitrite. These structures were also compared with respect to Cu site geometry, and were discussed in light of the pH dependence of enzyme activity, substrate affinity and gene expression.
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| 6. |
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| 7. |
- Jansson, Hanna, 1975, et al.
(författare)
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The crystal structure of the spinach plastocyanin double mutant G8D/L12E gives insight into its low reactivity towards photosystem 1 and cytochrome f
- 2003
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Ingår i: Biochimica et Biophysica Acta. - : Elsevier BV. - 0005-2728 .- 1879-2650. ; 1607:2-3, s. 203-210
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Tidskriftsartikel (refereegranskat)abstract
- Plastocyanin (Pc) is a copper-containing protein, which functions as an electron carrier between the cytochrome b6f and photosystem 1 (PS1) complexes in the photosynthetic electron transfer (ET) chain. The ET is mediated by His87 situated in the hydrophobic surface in the north region of Pc. Also situated in this region is Leu12, which mutated to other amino acids severely disturbs the ET from cytochrome f and to PS1, indicating the importance of the hydrophobic surface. The crystal structure of the Pc double mutant G8D/L12E has been determined to 2.0 Å resolution, with a crystallographic R-factor of 18.3% (Rfree=23.2%). A comparison with the wild-type structure reveals that structural differences are limited to the sites of the mutations. In particular, there is a small but significant change in the hydrophobic surface close to His87. Evidently, this leads to a mismatch in the reactive complex with the redox partners. For PS1 this results in a 20 times weaker binding and an eightfold slower ET as determined by kinetic measurements. The mutations that have been introduced do not affect the optical absorption spectrum. However, there is a small change in the EPR spectrum, which can be related to changes in the copper coordination geometry.
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