Folding of apocytochrome c in lipid micelles: formation of alpha-helix precedes membrane insertion.

Bryson, E; Rankin, SE; Carey, M; Watts, A; Pinheiro, T

Journal article

Folding of apocytochrome c in lipid micelles: formation of alpha-helix precedes membrane insertion.

Abstract:: Apocytochrome c, which in aqueous solution is largely unstructured, acquires a highly alpha-helical structure upon interaction with lipid. The alpha-helix content induced in apocytochrome c depends on the lipid system, and this folding process is driven by both electrostatic and hydrophobic lipid-protein interactions. The folding kinetic mechanism of apocytochrome c induced by zwitterionic micelles of lysophosphatidylcholine (L-PC), predominantly driven by hydrophobic lipid-protein interactions, was investigated by fluorescence stopped-flow measurements of Trp 59 and fluorescein-phosphatidylethanolamine-(FPE) labeled micelles, in combination with stopped-flow far-UV circular dichroism. It was found that formation of the alpha-helical structure of apocytochrome c precedes membrane insertion. The unfolded state in solution (U(W)) binds to the micelle surface in a helical conformation (I(S)) and is followed by insertion into the lipid micelle, i.e., formation of the final helical state H(L). Binding of apocytochrome c to the lipid micelle (U(W) --> I(S)) is concurrent with formation of a large fraction (75-100%, depending on lipid concentration) of the alpha-helical structure of the final lipid-inserted state H(L). The highly helical intermediate I(S) is formed on the time scale of 3-12 ms, depending on lipid concentration, and inserts into the lipid micelle (I(S) --> H(L)) in the time range of approximately 200 ms to >1 s, depending on lipid-to-protein ratio. The final lipid-inserted helical state H(L) in L-PC micelles has an alpha-helix content approximately 65% of that of cytochrome c in solution and has no compact stable tertiary structure as revealed by circular dichroism results.

Publication status:: Published

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APA Style

Bryson, E., Rankin, S. E., Carey, M., Watts, A., & Pinheiro, T. (1999). Folding of apocytochrome c in lipid micelles: formation of alpha-helix precedes membrane insertion. Biochemistry, 38(30), 9758–9767.

MLA Style

Bryson, E, et al. “Folding of Apocytochrome c in Lipid Micelles: Formation of Alpha-Helix Precedes Membrane Insertion.” Biochemistry, vol. 38, no. 30, 1999, pp. 9758–67.

Chicago Style

Bryson, E, SE Rankin, M Carey, A Watts, and T Pinheiro. 1999. “Folding of Apocytochrome c in Lipid Micelles: Formation of Alpha-Helix Precedes Membrane Insertion.” Biochemistry 38 (30): 9758–67.
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