Conservation of Lipid Binding Sites in Cytochrome bc Complexes1

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.

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Faculty Opinions recommendation of Identification of specific lipid-binding sites in integral membrane proteins.

Faculty Opinions – Post-Publication Peer Review of the Biomedical Literature ◽

10.3410/f.717948119.793453173 ◽

2012 ◽

Author(s):

Robert Vandenberg

Keyword(s):

Membrane Proteins ◽

Binding Sites ◽

Lipid Binding ◽

Integral Membrane Proteins ◽

Specific Lipid

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Structure, function, and regulation of myosin 1C.

Acta Biochimica Polonica ◽

10.18388/abp.2005_3450 ◽

2005 ◽

Vol 52 (2) ◽

pp. 373-380 ◽

Cited By ~ 29

Author(s):

Barbara Barylko ◽

Gwanghyun Jung ◽

Joseph P Albanesi

Keyword(s):

Plasma Membrane ◽

Binding Sites ◽

Subcellular Location ◽

Lipid Binding ◽

Tail Domain ◽

Anionic Lipid ◽

Myosin I ◽

Docking Proteins ◽

Neck Domain ◽

Anionic Lipids

Myosin 1C, the first mammalian single-headed myosin to be purified, cloned, and sequenced, has been implicated in the translocation of plasma membrane channels and transporters. Like other forms of myosin I (of which eight exist in humans) myosin 1C consists of motor, neck, and tail domains. The neck domain binds calmodulins more tightly in the absence than in the presence of Ca(2+). Release of calmodulins exposes binding sites for anionic lipids, particularly phosphoinositides. The tail domain, which has an isoelectic point of 10.5, interacts with anionic lipid headgroups. When both neck and tail lipid binding sites are engaged, the myosin associates essentially irreversibly with membranes. Despite this tight membrane binding, it is widely believed that myosin 1C docking proteins are necessary for targeting the enzyme to specific subcellular location. The search for these putative myosin 1C receptors is an active area of research.

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