Solid-State NMR Investigations of a Transmembrane Peptide having Interfacial Histidine Residues

Abstract

Membrane-spanning hydrophobic alpha-helical peptides are often flanked by interfacial aromatic or charged residues that may help to stabilize the transmembrane orientation. The synthetic neutral transmembrane peptide GWALP23 (acetyl-GGALW5LALALALALALALW19LAGA-ethanolamide) with two interfacial Trp residues has proved to be surprisingly well-behaved with minimal dynamic averaging in a stable transmembrane orientation in lipid-bilayer membranes of varying thickness. Replacing W5 with Y5 or F5 in GWALP23 was found to yield essentially the same average tilt and dynamics in several lipid bilayers (Biochemistry, 2014, 53, 3637–3645). To investigate the tilt, dynamics and pH dependence of GWALP23 with interfacial His residues, we have substituted W5 and W19 with histidine and have incorporated 2H-Ala labels at different positions within the core helix of peptide. We have employed solid state 2H-NMR spectroscopy to evaluate the peptide tilt with respect to the bilayer normal in aligned bilayers of DMPC and DLPC at pH near 4 and 8. As the peptide exhibits well-defined 2H quadrupolar splittings from 2H-alanine methyl groups in both lipids at specific pH, we are aiming to examine the transmembrane orientations by using the Geometric Analysis of Labeled Alanines (GALA) method. Further investigations of peptide helix behavior in other lipids, and with His residues at other locations, are underway.