title: Interactions of synthetic peptide analogs of the class A amphipathic helix with lipids. Evidence for the snorkel hypothesis.
abstract: Class A amphipathic helixes present in exchangeable plasma apolipoproteins are characterized by the location of positively charged amino acid residues at the non-polar-polar interface and negatively charged amino acid residues at the center of the polar face. The objectives of the present study were: (i) to investigate the role of hydrocarbon side chain length of the interfacial positively charged amino acid residues in the lipid affinity of class A amphipathic helixes, and (ii) to investigate the importance of the nature of interfacial charge in the lipid affinity of class A amphipathic helixes. Toward this end, lipid interactions of the following two analogs of the class A amphipathic helix, Ac-18A-NH2 (acetyl-Asp-Trp-Leu-Lys-Ala-Phe-Tyr- Asp-Lys-Val-Ala-Glu-Lys-Leu-Lys-Glu-Ala-Phe-NH2), and Ac-18A(Lys > Haa)-NH2 (acetyl-Asp-Trp-Leu-Haa-Ala-Phe-Tyr-Asp-Haa-Val-Ala-Glu-Haa-Leu-Haa-Glu- Ala-Phe-NH2) (Haa = homoaminoalanine), were studied. The side chain of Haa has two CH2 groups less than that of lysine. The lipid affinities of these two peptide analogs were compared with that of Ac-18R-NH2, an analog of Ac-18A-NH2 with positions of the charged amino acid residues reversed. The techniques used in these studies were circular dichroism, fluorescence spectroscopy, right-angle light scattering measurements, and differential scanning calorimetry. The results of these studies indicated the following rank order of lipid affinity: Ac-18A-NH2 > Ac-18A(Lys > Haa)-NH2 > Ac-18R-NH2. These results are in agreement with the "snorkel" model proposed earlier to explain the higher lipid affinity of class A amphipathic helixes (Segrest, J. P., Loof, H. D., Dohlman, J. G., Brouillette, C. G., and Anantharamaiah, G. M. (1990) Proteins Struct. Funct. Genetics 8, 103-117). In addition, it was observed from the differential scanning calorimetry studies that Ac-18A-NH2 and Ac-18A(Lys > Haa)-NH2 interact more strongly than Ac-18R-NH2 with negatively charged dimyristoyl phosphatidylglycerol. The weaker interaction of Ac-18R-NH2 with dimyristoyl phosphatidylglycerol is suggested to be due to electrostatic repulsion between the negatively charged lipid and the interfacial negative charges of the peptide.
authors.affiliation: Department of Medicine, University of Alabama-Birmingham Medical Center 35294.
authors.forename: V K
authors.initials: VK
authors.lastname: Mishra
authors.forename: M N
authors.initials: MN
authors.lastname: Palgunachari
authors.forename: J P
authors.initials: JP
authors.lastname: Segrest
authors.forename: G M
authors.initials: GM
authors.lastname: Anantharamaiah
mesh_terms: D000595:Amino Acid Sequence; D002942:Circular Dichroism; D004134:Dimyristoylphosphatidylcholine / Q000737:chemistry; D008027:Light; D008969:Molecular Sequence Data; D010455:Peptides / Q000138:chemical synthesis / Q000737:chemistry*; D010713:Phosphatidylcholines / Q000737:chemistry*; D010715:Phosphatidylglycerols / Q000737:chemistry*; D011487:Protein Conformation; D012542:Scattering, Radiation; D013050:Spectrometry, Fluorescence; D013056:Spectrophotometry, Ultraviolet
chemical_list: D010455:Peptides; D010713:Phosphatidylcholines; D010715:Phosphatidylglycerols; C002773:dimyristoylphosphatidylglycerol; D004134:Dimyristoylphosphatidylcholine