title: Changes in helical content or net charge of apolipoprotein C-I alter its affinity for lipid/water interfaces.
abstract: Amphipathic α-helices mediate binding of exchangeable apolipoproteins to lipoproteins. To probe the role of α-helical structure in protein-lipid interactions, we used oil-drop tensiometry to characterize the interfacial behavior of apolipoprotein C-I (apoC-I) variants at triolein/water (TO/W) and 1-palmitoyl-2-oleoylphosphatidylcholine/triolein/water (POPC/TO/W) interfaces. ApoC-I, the smallest apolipoprotein, has two amphipathic α-helices. Mutants had single Pro or Ala substitutions that resulted in large differences in helical content in solution and on phospholipids. The ability of apoC-I to bind TO/W and POPC/TO/W interfaces correlated strongly with α-helical propensity. On binding these interfaces, peptides with higher helical propensity increased surface pressure to a greater extent. Likewise, peptide exclusion pressure at POPC/TO/W interfaces increased with greater helical propensity. ApoC-I retention on TO/W and POPC/TO/W interfaces correlated strongly with phospholipid-bound helical content. On compression of these interfaces, peptides with higher helical content were ejected at higher pressures. Substitution of Arg for Pro in the N-terminal α-helix altered net charge and reduced apoC-I affinity for POPC/TO/W interfaces. Our results suggest that peptide-lipid interactions drive α-helix binding to and retention on lipoproteins. Point mutations in small apolipoproteins could significantly change α-helical propensity or charge, thereby disrupting protein-lipid interactions and preventing the proteins from regulating lipoprotein catabolism at high surface pressures.
authors.affiliation: Department of Physiology and Biophysics, Boston University School of Medicine, Boston, MA, USA.
authors.forename: Nathan L
authors.initials: NL
authors.lastname: Meyers
authors.forename: Libo
authors.initials: L
authors.lastname: Wang
authors.forename: Olga
authors.initials: O
authors.lastname: Gursky
authors.forename: Donald M
authors.initials: DM
authors.lastname: Small
mesh_terms: D053302:Apolipoprotein C-I / Q000737:chemistry* / Q000235:genetics; D006801:Humans; D010713:Phosphatidylcholines / Q000737:chemistry*; D017354:Point Mutation; D017433:Protein Structure, Secondary; D013499:Surface Properties; D014304:Triolein / Q000737:chemistry*; D014867:Water / Q000737:chemistry*
chemical_list: C505803:APOC1 protein, human; D053302:Apolipoprotein C-I; D010713:Phosphatidylcholines; D014867:Water; D014304:Triolein; C028694:1-palmitoyl-2-oleoylphosphatidylcholine
keywords: drop tensiometry; protein-lipid interaction; surface chemistry