3ph2
Structure of the imidazole-adduct of the Phormidium laminosum cytochrome c6 Q51V variant
Structural highlights
FunctionF2Z292_PHOLA Functions as an electron carrier between membrane-bound cytochrome b6-f and photosystem I in oxygenic photosynthesis.[HAMAP-Rule:MF_00594] Publication Abstract from PubMedThe amino acid at position 51 in the cytochrome c (6) family is responsible for modulating over 100 mV of heme midpoint redox potential. As part of the present work, the X-ray structure of the imidazole adduct of the photosynthetic cytochrome c (6) Q51V variant from Phormidium laminosum has been determined. The structure reveals the axial Met ligand is dissociated from the heme iron but remains inside the heme pocket and the Omega-loop housing the Met ligand is stabilized through polar interactions with the imidazole and heme propionate-6. The latter is possible owing to a 180 degrees rotation of both heme propionates upon imidazole binding. From equilibrium and kinetic studies, a Val residue at position 51 increases the stability of the Fe-S(Met) interaction and also affects the dynamics associated with imidazole binding. In this respect, the k (obs) for imidazole binding to Arabidopsis thaliana cytochrome c (6A), which has a Val at the position equivalent to position 51 in photosynthetic cytochrome c (6), was found to be independent of imidazole concentration, indicating that the binding process is limited by the Met dissociation rate constant (about 1 s(-1)). For the cytochrome c (6) Q51V variant, imidazole binding was suppressed in comparison with the wild-type protein and the V52Q variant of cytochrome c (6A) was found to bind imidazole readily. We conclude that the residue type at position 51/52 in the cytochrome c (6) family is additionally responsible for tuning the stability of the heme iron-Met bond and the dynamic properties of the ferric protein fold associated with endogenous ligand binding. Structural and kinetic studies of imidazole binding to two members of the cytochrome c (6) family reveal an important role for a conserved heme pocket residue.,Rajagopal BS, Wilson MT, Bendall DS, Howe CJ, Worrall JA J Biol Inorg Chem. 2011 Jan 26. PMID:21267610[1] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. See AlsoReferences
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