5dqr
From Proteopedia
The crystal structure of Arabidopsis 7-hydroxymethyl chlorophyll a reductase (HCAR)
Structural highlights
FunctionHCAR_ARATH Probable iron-sulfur flavoprotein that converts 7-hydroxymethyl chlorophyll a to chlorophyll a using ferredoxin as a reducing equivalent. Catalyzes the reduction of a hydroxymethyl group to a methyl group. Belongs to the chlorophyll catabolic enzymes (CCEs).[1] Publication Abstract from PubMed7-Hydroxymethyl chlorophyll a reductase (HCAR) catalyzes the second half-reaction in chlorophyll b to chlorophyll a conversion. HCAR is required for the degradation of light-harvesting complexes and is necessary for efficient photosynthesis by balancing the chlorophyll a/b ratio. Reduction of the hydroxymethyl group uses redox cofactors [4Fe-4S] cluster and FAD to transfer electrons and is difficult because of the strong carbon-oxygen bond. Here, we report the crystal structure of Arabidopsis HCAR at 2.7-A resolution and reveal that two [4Fe-4S]clusters and one FAD within a very short distance form a consecutive electron pathway to the substrate pocket. In vitro kinetic analysis confirms the ferredoxin-dependent electron transport chain, thus supporting a proton-activated electron transfer mechanism. HCAR resembles a partial reconstruction of an archaeal F420-reducing [NiFe] hydrogenase, which suggests a common mode of efficient proton-coupled electron transfer through conserved cofactor arrangements. Furthermore, the trimeric form of HCAR provides a biological clue of its interaction with light-harvesting complex II. Crystal Structure and Catalytic Mechanism of 7-Hydroxymethyl Chlorophyll a Reductase.,Wang X, Liu L J Biol Chem. 2016 Jun 17;291(25):13349-59. doi: 10.1074/jbc.M116.720342. Epub, 2016 Apr 12. PMID:27072131[2] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. References
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