2E74

Crystal Structure of the Cytochrome b6f Complex from M.laminosus

Summary for 2E74

• Entry DOI: 10.2210/pdb2e74/pdb
• Related: 2E75 2E76
• Descriptor: Cytochrome b6, PROTOPORPHYRIN IX CONTAINING FE, UNDECYL-MALTOSIDE, ... (17 entities in total)
• Functional Keywords: photosynthesis, cytochrome f, rieske iron-sulfur protein, heme cn
• Biological source: Mastigocladus laminosus; More
• Cellular location: Cellular thylakoid membrane; Multi-pass membrane protein: P83791 P83792; Cellular thylakoid membrane; Single-pass membrane protein: P83793 P83795 P83796 P83797 P83798; Cellular thylakoid membrane; Single-pass membrane protein (By similarity): P83794
• Total number of polymer chains: 8
• Total formula weight: 116332.20

Authors

Cramer, W.A.,Yamashita, E.,Zhang, H. (deposition date: 2007-01-05, release date: 2007-06-12, Last modification date: 2024-11-20)

Primary citation

Yamashita, E.,Zhang, H.,Cramer, W.A.
Structure of the Cytochrome b(6)f Complex: Quinone Analogue Inhibitors as Ligands of Heme c(n)
J.Mol.Biol., 370:39-52, 2007

PubMed Abstract: 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.

PubMed: 17498743
DOI: 10.1016/j.jmb.2007.04.011

Experimental method

X-RAY DIFFRACTION (3 Å)