Conformation of human apolipoprotein C-I in a lipid-mimetic environment determined by CD and NMR spectroscopy.
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.
Rozek
A
A
Department of Chemistry and Institute of Molecular Biology and Biochemistry, Simon Fraser University, Burnaby, British Columbia Canada.
Sparrow
J T
JT
Weisgraber
K H
KH
Cushley
R J
RJ
D000595:Amino Acid Sequence; D053302:Apolipoprotein C-I; D001056:Apolipoproteins C / Q000097:blood / Q000737:chemistry* / Q000235:genetics; D001665:Binding Sites; D002942:Circular Dichroism; D004563:Electrochemistry; D004789:Enzyme Activation; D006801:Humans; D066298:In Vitro Techniques; D008055:Lipids / Q000737:chemistry; D009682:Magnetic Resonance Spectroscopy; D008958:Models, Molecular; D008969:Molecular Sequence Data; D011487:Protein Conformation; D017433:Protein Structure, Secondary; D012967:Sodium Dodecyl Sulfate; D002785:Sterol O-Acyltransferase / Q000378:metabolism; D013329:Structure-Activity Relationship
D053302:Apolipoprotein C-I; D001056:Apolipoproteins C; D008055:Lipids; D012967:Sodium Dodecyl Sulfate; D002785:Sterol O-Acyltransferase