Lipid functions in cytochrome bc complexes: an odd evolutionary transition in a membrane protein structure.

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TitleLipid functions in cytochrome bc complexes: an odd evolutionary transition in a membrane protein structure.
Publication TypeJournal Article
Year of Publication2012
AuthorsS Hasan, S, Cramer, WA
JournalPhilos Trans R Soc Lond B Biol Sci
Date Published2012 Dec 19
KeywordsBinding Sites, Cell Membrane, Chlamydomonas reinhardtii, Cyanobacteria, Cytochrome b6f Complex, Electron Transport, Evolution, Molecular, Light-Harvesting Protein Complexes, Membrane Lipids, Membrane Proteins, Oxidation-Reduction, Photosynthesis, Photosystem I Protein Complex, Protein Binding, Protein Stability, Protein Structure, Secondary, Protein Structure, Tertiary, Signal Transduction, Structure-Activity Relationship

Lipid-binding sites and properties were compared in the hetero-oligomeric cytochrome (cyt) b(6)f and the yeast bc(1) complexes that function, respectively, in photosynthetic and respiratory electron transport. Seven lipid-binding sites in the monomeric unit of the dimeric cyanobacterial b(6)f complex overlap four sites in the Chlamydomonas reinhardtii algal b(6)f complex and four in the yeast bc(1) complex. The proposed lipid functions include: (i) interfacial-interhelix mediation between (a) the two 8-subunit monomers of the dimeric complex, (b) between the core domain (cyt b, subunit IV) and the six trans membrane helices of the peripheral domain (cyt f, iron-sulphur protein (ISP), and four small subunits in the boundary 'picket fence'); (ii) stabilization of the ISP domain-swapped trans-membrane helix; (iii) neutralization of basic residues in the single helix of cyt f and of the ISP; (iv) a 'latch' to photosystem I provided by the β-carotene chain protruding through the 'picket fence'; (v) presence of a lipid and chlorophyll a chlorin ring in b(6)f in place of the eighth helix in the bc(1) cyt b polypeptide. The question is posed of the function of the lipid substitution in relation to the evolutionary change between the eight and seven helix structures of the cyt b polypeptide. On the basis of the known n-side activation of light harvesting complex II (LHCII) kinase by the p-side level of plastoquinol, one possibility is that the change was directed by the selective advantage of p- to n-side trans membrane signalling functions in b(6)f, with the lipid either mediating this function or substituting for the trans membrane helix of a signalling protein lost in crystallization.

Alternate JournalPhilos. Trans. R. Soc. Lond., B, Biol. Sci.
PubMed ID23148267
PubMed Central IDPMC3497066
Grant ListR01 GM038323 / GM / NIGMS NIH HHS / United States
R56 GM038323 / GM / NIGMS NIH HHS / United States
GM-038323 / GM / NIGMS NIH HHS / United States