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Folding of apocytochrome c induced by the interaction with negatively charged lipid micelles proceeds via a collapsed intermediate state

Published online by Cambridge University Press:  01 February 1999

SAFFRON E. RANKIN
Affiliation:
Department of Biological Sciences, Gibbet Hill Road, University of Warwick, Coventry CV4 7AL, United Kingdom
ANTHONY WATTS
Affiliation:
Department of Biochemistry, University of Oxford, South Parks Road, Oxford OX1 3QU, United Kingdom
HEINRICH RODER
Affiliation:
Institute for Cancer Research, Fox Chase Cancer Center, 7701 Burholme Avenue, Philadelphia, Pennsylvania 19111
TERESA J.T. PINHEIRO
Affiliation:
Department of Biological Sciences, Gibbet Hill Road, University of Warwick, Coventry CV4 7AL, United Kingdom
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Abstract

Unfolded apocytochrome c acquires an α-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 (IC). 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 IC through a more extended state associated with the membrane surface (IS). While IC appears to be as compact as salt-induced compact states in solution with substantial α-helix content, the final lipid-inserted state (Hmic) is as compact as the unfolded state in solution at pH 5 and has an α-helix content which resembles that of native cytochrome c.

Type
Research Article
Copyright
© 1999 The Protein Society

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