Position Dependent Orientation Difference of Transmembrane Peptides Flanked by Single or Multiple Histidine Residues

Abstract

GWALP23, a constructive low-dynamic model peptide framework, widens the range of protein-lipid interactions that can be investigated when potentially charged residues are present. In this context, we have examined the effects of single or pairs of histidine residues. To this end, we substituted residues H8 and H16 into the parent sequence (acetyl-GGALW5LAL8ALALALAL16ALW19LAGA-amide) of GWALP23. The 2H-NMR spectra of 2H-labeled core alanine residues show, interestingly, no titration dependency from pH 2-8, yet a difference in bilayer thickness-dependent orientation. In DLPC lipid bilayers, a quadrupolar wave analysis indicates a tilted transmembrane helix similar to that of the parent GWALP23 peptide. With respect to DOPC membranes, nevertheless, the peptide Ala residues display a wide range of 2H quadrupolar splittings (about 1.5 −30 kHz). The helix adopts a surface bound orientation on DOPC membranes, however alanine A7 does not fit within the core helix. Additional single histidine peptides, with H2 or H22 substituted into the parent sequence, display tilted transmembrane orientations in bilayers of DLPC or DOPC, with little or no pH dependence of the orientations from pH 2 to pH 8. Results from H2,22WALP23 will be compared with those observed when only H2 or H22 is present. The more central histidines 8 and 16 can lead to a helix transition from membrane-spanning in DLPC (and most likely also in DMPC) to a surface orientation when the lipid bilayer is the thicker DOPC.