| 1. |
- Lundberg, Erik, et al.
(författare)
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Crystal structure of the TL29 protein from Arabidopsis thaliana : An APX homolog without peroxidase activity
- 2011
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Ingår i: Journal of Structural Biology. - : Elsevier. - 1047-8477 .- 1095-8657. ; 176:1, s. 24-31
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Tidskriftsartikel (refereegranskat)abstract
- TL29 is a plant-specific protein found in the thylakoid lumen of chloroplasts. Despite the putative requirement in plants for a peroxidase close to the site of photosynthetic oxygen production, and the sequence homology of TL29 to ascorbate peroxidases, so far biochemical methods have not shown this enzyme to possess peroxidase activity. Here we report the three-dimensional X-ray crystal structure of recombinant TL29 from Arabidopsis thaliana at a resolution of 2.5 Å. The overall structure of TL29 is mainly alpha helical with six longer and six shorter helical segments. The TL29 structure resembles that of typical ascorbate peroxidases, however, crucial differences were found in regions that would be important for heme and ascorbate binding. Such differences suggest it to be highly unlikely that TL29 functions as a peroxidase.
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| 2. |
- Storm, Patrik, 1966-, et al.
(författare)
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Refolding and enzyme kinetic studies on the ferrochelatase of the cyanobacterium synechocystis sp. PCC 6803
- 2013
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Ingår i: PLOS ONE. - : Public Library of Science (PLoS). - 1932-6203. ; 8:2
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Tidskriftsartikel (refereegranskat)abstract
- Heme is a cofactor for proteins participating in many important cellular processes, including respiration, oxygen metabolism and oxygen binding. The key enzyme in the heme biosynthesis pathway is ferrochelatase (protohaem ferrolyase, EC 4.99.1.1), which catalyzes the insertion of ferrous iron into protoporphyrin IX. In higher plants, the ferrochelatase enzyme is localized not only in mitochondria, but also in chloroplasts. The plastidic type II ferrochelatase contains a C-terminal chlorophyll a/b (CAB) motif, a conserved hydrophobic stretch homologous to the CAB domain of plant light harvesting proteins and light-harvesting like proteins. This type II ferrochelatase, found in all photosynthetic organisms, is presumed to have evolved from the cyanobacterial ferrochelatase. Here we describe a detailed enzymological study on recombinant, refolded and functionally active type II ferrochelatase (FeCh) from the cyanobacterium Synechocystis sp. PCC 6803. A protocol was developed for the functional refolding and purification of the recombinant enzyme from inclusion bodies, without truncation products or soluble aggregates. The refolded FeCh is active in its monomeric form, however, addition of an N-terminal His6-tag has significant effects on its enzyme kinetics. Strikingly, removal of the C-terminal CAB-domain led to a greatly increased turnover number, kcat, compared to the full length protein. While pigments isolated from photosynthetic membranes decrease the activity of FeCh, direct pigment binding to the CAB domain of FeCh was not evident.
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| 3. |
- Ådén, Jörgen, 1980-, et al.
(författare)
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Extraordinary μs-ms backbone dynamics in Arabidopsis thaliana peroxiredoxin Q
- 2011
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Ingår i: Biochimica et Biophysica Acta. - : Elsevier. - 0006-3002 .- 1878-2434. ; 1814:12, s. 1880-1890
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Tidskriftsartikel (refereegranskat)abstract
- Peroxiredoxin Q (PrxQ) isolated from Arabidopsis thaliana belongs to a family of redox enzymes called peroxiredoxins, which are thioredoxin- or glutaredoxin-dependent peroxidases acting to reduce peroxides and in particular hydrogen peroxide. PrxQ cycles between an active reduced state and an inactive oxidized state during its catalytic cycle. The catalytic mechanism involves a nucleophilic attack of the catalytic cysteine on hydrogen peroxide to generate a sulfonic acid intermediate with a concerted release of a water molecule. This intermediate is subsequently relaxed by the reaction of a second cysteine, denoted the resolving cysteine, generating an intramolecular disulfide bond and release of a second water molecule. PrxQ is recycled to the active state by a thioredoxin-dependent reduction. Previous structural studies of PrxQ homologues have provided the structural basis for the switch between reduced and oxidized conformations. Here, we have performed a detailed study of the activity, structure and dynamics of PrxQ in both the oxidized and reduced states. Reliable and experimentally validated structural models of PrxQ in both oxidation states were generated using homology based modeling. Analysis of NMR spin relaxation rates shows that PrxQ is monomeric in both oxidized and reduced states. As evident from R(2) relaxation rates the reduced form of PrxQ undergoes unprecedented dynamics on the slow μs-ms timescale. The ground state of this conformational dynamics is likely the stably folded reduced state as implied by circular dichroism spectroscopy. We speculate that the extensive dynamics is intimately related to the catalytic function of PrxQ.
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