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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.

Original publication

DOI

10.1110/ps.8.2.381

Type

Journal article

Journal

Protein Sci

Publication Date

02/1999

Volume

8

Pages

381 - 393

Keywords

Animals, Apoproteins, Cytochrome c Group, Cytochromes c, Horses, Hydrogen-Ion Concentration, Iodine, Kinetics, Lipids, Lysophospholipids, Micelles, Myocardium, Protein Conformation, Protein Folding, Protein Structure, Secondary, Spectrometry, Fluorescence, Tryptophan