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Role of secondary structure in protein‐lipid interactions: decreases in the helical content of apolipoprotein C‐I lower its affinity for triolein/water and phospholipid/triolein/water interfaces
Author(s) -
Meyers Nathan,
Wang Libo,
Gursky Olga,
Small Donald
Publication year - 2013
Publication title -
the faseb journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.709
H-Index - 277
eISSN - 1530-6860
pISSN - 0892-6638
DOI - 10.1096/fasebj.27.1_supplement.1208.9
Subject(s) - triolein , popc , chemistry , aqueous solution , amphiphile , protein secondary structure , phospholipid , helix (gastropod) , crystallography , chromatography , biochemistry , biophysics , organic chemistry , membrane , polymer , enzyme , ecology , snail , lipase , copolymer , biology
Binding of exchangeable apolipoproteins to lipoprotein surfaces is mediated by amphipathic α‐helices. To probe the role of α‐helical structure in protein‐lipid interactions, we used oil‐drop tensiometry to characterize the interfacial behavior of apolipoproteinC‐I (apoC‐I) and its mutants at TO/W and palmitoyloleoylphosphatidylcholine/triolein/water (POPC/TO/W) interfaces. ApoC‐I, the smallest apolipoprotein (57 amino acids), has two amphipathic α‐helices from residues 7–29 and 34–47. Mutants contained single Pro or Ala substitutions, such that they differed in helical content in solution (0–48%) and on lipid (40–75%). Tensiometry results showed that apoC‐I binding to and modification of TO/W and POPC/TO/W interfaces correlated strongly with aqueous helical content. On binding both types of interfaces, peptides with higher aqueous helical content increased surface pressure (Π) to a greater extent. The Π at which peptides were excluded from POPC/TO/W interfaces increased with greater aqueous helical content. ApoC‐I retention on TO/W and POPC/TO/W interfaces correlated strongly with lipid‐bound helical content. Peptides with higher lipid‐bound helical content were ejected from compressed interfaces at higher Π. These results support a model in which α‐helix affinity for lipoproteins increases with greater aqueous and lipid‐bound helical content. This model explains the higher lipid affinity of apoC‐I than apoC‐II, whose two lipid binding α‐helices differ from those of apoC‐I primarily in helical content.