5owg
Structure of PcyX_EBK42635
Structural highlights
Publication Abstract from PubMedFerredoxin-dependent bilin reductases (FDBRs) are a class of enzymes reducing the heme metabolite biliverdin IXalpha (BV) to form open-chain tetrapyrroles used for light-perception and light-harvesting in photosynthetic organisms. Thus far, seven FDBR families have been identified, each catalyzing a distinct reaction and either transferring two or four electrons from ferredoxin onto the substrate. The newest addition to the family is PcyX, originally identified from metagenomics data derived from phage. Phylogenetically, PcyA is the closest relative catalyzing the reduction of BV to phycocyanobilin. PcyX on the other hand converts the same substrate to phycoerythrobilin, resembling the reaction catalyzed by cyanophage PebS. Within this study we aimed at understanding the evolution of catalytic activities within FDBRs using PcyX as an example. Additional members of the PcyX clade and a remote member of the PcyA family were investigated in order to gain insights into catalysis. Biochemical data in combination with the PcyX crystal structure revealed that a conserved aspartate-histidine pair is critical for activity. Interestingly, the same residues are part of a catalytic Asp-His-Glu triad in PcyA, including an additional Glu. While this Glu residue is replaced by Asp in PcyX, it is not involved in catalysis. Substitution back to a Glu failed to convert PcyX to a PcyA. Therefore, the change in regiospecificity is not only caused by individual catalytic amino acid residues. Rather the combination of the architecture of the active site with the positioning of the substrate triggers specific proton transfer yielding the individual phycobilin products. This article is protected by copyright. All rights reserved. Evolution and molecular mechanism of four-electron reducing ferredoxin-dependent bilin reductases from oceanic phages.,Ledermann B, Schwan M, Sommerkamp JA, Hofmann E, Beja O, Frankenberg-Dinkel N FEBS J. 2017 Nov 20. doi: 10.1111/febs.14341. PMID:29156487[1] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. References
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