Folding of apocytochrome c induced by the interaction with negatively charged lipid micelles proceeds via a collapsed intermediate state.
Unfolded apocytochrome c acquires an alpha-helical conformation upon interaction with lipid. Folding kinetic results below and above the lipid's CMC, together with energy transfer measurements of lipid bound states, and salt-induced compact states in solution, show that the folding transition of apocytochrome c from the unfolded state in solution to a lipid-inserted helical conformation proceeds via a collapsed intermediate state (I(C)). This initial compact state is driven by a hydrophobic collapse of the polypeptide chain in the absence of the heme group and may represent a heme-free analogue of an early compact intermediate detected on the folding pathway of cytochrome c in solution. Insertion into the lipid phase occurs via an unfolding step of I(C) through a more extended state associated with the membrane surface (I(S)). While I(C) appears to be as compact as salt-induced compact states in solution with substantial alpha-helix content, the final lipid-inserted state (Hmic) is as compact as the unfolded state in solution at pH 5 and has an alpha-helix content which resembles that of native cytochrome c.
Department of Biological Sciences, University of Warwick, Coventry, United Kingdom.
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D000818:Animals; D001059:Apoproteins / Q000032:analysis* / Q000378:metabolism; D003574:Cytochrome c Group / Q000032:analysis* / Q000378:metabolism; D045304:Cytochromes c; D006736:Horses; D006863:Hydrogen-Ion Concentration; D007455:Iodine / Q000737:chemistry; D007700:Kinetics; D008055:Lipids / Q000032:analysis*; D008246:Lysophospholipids / Q000032:analysis / Q000493:pharmacokinetics; D008823:Micelles; D009206:Myocardium / Q000737:chemistry; D011487:Protein Conformation; D017510:Protein Folding; D017433:Protein Structure, Secondary; D013050:Spectrometry, Fluorescence; D014364:Tryptophan / Q000737:chemistry
D001059:Apoproteins; D003574:Cytochrome c Group; D008055:Lipids; D008246:Lysophospholipids; D008823:Micelles; C026223:lysophosphatidylglycerol; D014364:Tryptophan; D045304:Cytochromes c; D007455:Iodine