title: Effect of variations in the structure of a polyleucine-based alpha-helical transmembrane peptide on its interaction with phosphatidylglycerol bilayers.
abstract: High-sensitivity differential scanning calorimetry and Fourier transform infrared spectroscopy were used to study the interaction of a cationic alpha-helical transmembrane peptide, acetyl-Lys(2)-Leu(24)-Lys(2)-amide (L(24)), and members of the homologous series of anionic n-saturated diacyl phosphatidylglycerols (PGs). Analogues of L(24), in which the lysine residues were replaced by 2,3-diaminopropionic acid (L(24)DAP), or in which a leucine residue at each end of the polyleucine sequence was replaced by a tryptophan (WL(22)W), were also studied to investigate the roles of lysine side-chain snorkeling and aromatic side-chain interactions with the interfacial region of phospholipid bilayers. The gel/liquid-crystalline phase transition temperature of the host PG bilayers is altered by these peptides in a hydrophobic mismatch-dependent manner, as previously found with zwitterionic phosphatidylcholine (PC) bilayers. However, all three peptides reduce the phase transition temperature and enthalpy to a greater extent in anionic PG bilayers than in zwitterionic PC bilayers, with WL(22)W having the largest effect. All three peptides form very stable alpha-helices in PG bilayers, but small conformational changes are induced in response to a mismatch between peptide hydrophobic length and gel-state lipid bilayer hydrophobic thickness. Moreover, electrostatic and hydrogen-bonding interactions occur between the terminal lysine residues of L(24) and L(24)DAP and the polar headgroups of PG bilayers. However, such interactions were not observed in PG/WL(22)W bilayers, suggesting that the cation-pi interactions between the tryptophan and lysine residues predominate. These results indicate that the lipid-peptide interactions are affected not only by the hydrophobic mismatch between these peptides and the host lipid bilayer, but also by the tryptophan-modulated electrostatic and hydrogen-bonding interactions between the positively charged lysine residues at the termini of these peptides and the negatively charged polar headgroups of the PG bilayers.
authors.affiliation: Department of Biochemistry, University of Alberta, Edmonton, Alberta, Canada T6G 2H7.
authors.forename: Feng
authors.initials: F
authors.lastname: Liu
authors.forename: Ruthven N A H
authors.initials: RN
authors.lastname: Lewis
authors.forename: Robert S
authors.initials: RS
authors.lastname: Hodges
authors.forename: Ronald N
authors.initials: RN
authors.lastname: McElhaney
mesh_terms: D002152:Calorimetry, Differential Scanning; D057927:Hydrophobic and Hydrophilic Interactions; D008051:Lipid Bilayers / Q000737:chemistry* / Q000378:metabolism; D008239:Lysine / Q000737:chemistry; D008565:Membrane Proteins / Q000737:chemistry* / Q000378:metabolism; D010455:Peptides / Q000737:chemistry* / Q000378:metabolism; D010715:Phosphatidylglycerols / Q000737:chemistry* / Q000378:metabolism; D017433:Protein Structure, Secondary; D017550:Spectroscopy, Fourier Transform Infrared; D055672:Static Electricity; D013329:Structure-Activity Relationship; D013696:Temperature; D014364:Tryptophan / Q000737:chemistry
chemical_list: D008051:Lipid Bilayers; D008565:Membrane Proteins; D010455:Peptides; D010715:Phosphatidylglycerols; C027819:polyleucine; D014364:Tryptophan; D008239:Lysine