Conformation of human apolipoprotein C-I in a lipid-mimetic environment determined by CD and NMR spectroscopy.Rozek, A., Sparrow, J.T., Weisgraber, K.H., Cushley, R.J.
(1999) Biochemistry 38: 14475-14484
- PubMed: 10545169
- DOI: https://doi.org/10.1021/bi982966h
- Primary Citation of Related Structures:
- PubMed Abstract:
The high-resolution conformation of human apoC-I in complexes with sodium dodecyl sulfate (SDS) is presented. As estimated from CD data, apoC-I adopts 54% helical secondary structure when bound to SDS, which is similar to the helical content previously found with phospholipids. The NMR-derived conformation of apoC-I is composed of two amphipathic helices, residues 7-29 and 38-52, separated by a flexible linker. The N-terminal helix contains a mobile hinge involving residues 12-15. The hydrophobic side chains cluster on the nonpolar face of both helices, thus forming two discrete lipid-binding sites in the N-terminal helix and one in the C-terminal helix. As suggested by amide proton resonance line widths and deuterium exchange rates, the N-terminal helix is more flexible and may bind less tightly to the detergent than the C-terminal helix. The different mobility of both helices appears to be related to side-chain composition, rather than length of the amphipathic helix, and may play a role in the function of apoC-I as an activator of lecithin:cholesterol acyltransferase (LCAT). A model is suggested in which the C-terminal helix serves as a lipid anchor while the N-terminal helix may hinge off the lipid surface to make specific contacts with LCAT.
Department of Chemistry and Institute of Molecular Biology and Biochemistry, Simon Fraser University, Burnaby, British Columbia Canada.