2e74
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Crystal Structure of the Cytochrome b6f Complex from M.laminosus
OverviewOverview
A native structure of the cytochrome b(6)f complex with improved, resolution was obtained from crystals of the complex grown in the presence, of divalent cadmium. Two Cd(2+) binding sites with different occupancy, were determined: (i) a higher affinity site, Cd1, which bridges His143 of, cytochrome f and the acidic residue, Glu75, of cyt b(6); in addition, Cd1, is coordinated by 1-2 H(2)O or 1-2 Cl(-); (ii) a second site, Cd2, of, lower affinity for which three identified ligands are Asp58 (subunit IV), Glu3 (PetG subunit) and Glu4 (PetM subunit). Binding sites of quinone, analogue inhibitors were sought to map the pathway of transfer of the, lipophilic quinone across the b(6)f complex and to define the function of, the novel heme c(n). Two sites were found for the chromone ring of the, tridecyl-stigmatellin (TDS) quinone analogue inhibitor, one near the, p-side [2Fe-2S] cluster. A second TDS site was found on the n-side of the, complex facing the quinone exchange cavity as an axial ligand of heme, c(n). A similar binding site proximal to heme c(n) was found for the, n-side inhibitor, NQNO. Binding of these inhibitors required their, addition to the complex before lipid used to facilitate crystallization., The similar binding of NQNO and TDS as axial ligands to heme c(n) implies, that this heme utilizes plastoquinone as a natural ligand, thus defining, an electron transfer complex consisting of hemes b(n), c(n), and PQ, and, the pathway of n-side reduction of the PQ pool. The NQNO binding site, explains several effects associated with its inhibitory action: the, negative shift in heme c(n) midpoint potential, the increased amplitude of, light-induced heme b(n) reduction, and an altered EPR spectrum attributed, to interaction between hemes c(n) and b(n). A decreased extent of heme, c(n) reduction by reduced ferredoxin in the presence of NQNO allows, observation of the heme c(n) Soret band in a chemical difference spectrum.
About this StructureAbout this Structure
2E74 is a Protein complex structure of sequences from Mastigocladus laminosus with CD, HEM, FES, CLA, BCR, OPC, UMQ and SQD as ligands. Active as Plastoquinol--plastocyanin reductase, with EC number 1.10.99.1 Full crystallographic information is available from OCA.
ReferenceReference
Structure of the Cytochrome b(6)f Complex: Quinone Analogue Inhibitors as Ligands of Heme c(n)., Yamashita E, Zhang H, Cramer WA, J Mol Biol. 2007 Jun 29;370(1):39-52. Epub 2007 Apr 12. PMID:17498743
Page seeded by OCA on Wed Nov 21 09:58:18 2007