title: Unfolding and refolding of cytochrome c driven by the interaction with lipid micelles.
abstract: Binding of native cyt c to L-PG micelles leads to a partially unfolded conformation of cyt c. This micelle-bound state has no stable tertiary structure, but remains as alpha-helical as native cyt c in solution. In contrast, binding of the acid-unfolded cyt c to L-PG micelles induces folding of the polypeptide, resulting in a similar helical state to that originated from the binding of native cyt c to L-PG micelles. Far-ultraviolet (UV) circular dichroism (CD) spectra showed that this common micelle-associated helical state (HL) has a native-like alpha-helix content, but is highly expanded without a tightly packed hydrophobic core, as revealed by tryptophan fluorescence, near-UV, and Soret CD spectroscopy. The kinetics of the interaction of native and acid-unfolded cyt c was investigated by stopped-flow tryptophan fluorescence. Formation of H(L) from the native state requires the disruption of the tightly packed hydrophobic core in the native protein. This micelle-induced unfolding of cyt c occurs at a rate approximately 0.1 s(-1), which is remarkably faster in the lipid environment compared with the expected rate of unfolding in solution. Refolding of acid-unfolded cyt c with L-PG micelles involves an early highly helical collapsed state formed during the burst phase (<3 ms), and the observed main kinetic event reports on the opening of this early compact intermediate prior to insertion into the lipid micelle.
authors.affiliation: Department of Biological Sciences, University of Warwick, Coventry, United Kingdom.
authors.forename: N
authors.initials: N
authors.lastname: Sanghera
authors.forename: T J
authors.initials: TJ
authors.lastname: Pinheiro
mesh_terms: D002942:Circular Dichroism; D003574:Cytochrome c Group / Q000737:chemistry*; D007700:Kinetics; D008246:Lysophospholipids / Q000737:chemistry*; D008823:Micelles; D017510:Protein Folding; D013050:Spectrometry, Fluorescence
chemical_list: D003574:Cytochrome c Group; D008246:Lysophospholipids; D008823:Micelles; C026223:lysophosphatidylglycerol