Geometry and intrinsic tilt of a tryptophan-anchored transmembrane alpha-helix determined by (2)H NMR.
We used solid-state deuterium NMR spectroscopy and an approach involving geometric analysis of labeled alanines (GALA method) to examine the structure and orientation of a designed synthetic hydrophobic, membrane-spanning alpha-helical peptide in phosphatidylcholine (PC) bilayers. The 19-amino-acid peptide consists of an alternating leucine and alanine core, flanked by tryptophans that serve as interfacial anchors: acetyl-GWW(LA)(6)LWWA-ethanolamine (WALP19). A single deuterium-labeled alanine was introduced at different positions within the peptide. Peptides were incorporated in oriented bilayers of dilauroyl- (di-C12:0-), dimyristoyl- (di-C14:0-), or dioleoyl- (di-C18:1(c)-) phosphatidylcholine. The NMR data fit well to a WALP19 orientation characterized by a distinctly nonzero tilt, approximately 4 degrees from the membrane normal, and rapid reorientation about the membrane normal in all three lipids. Although the orientation of WALP19 varies slightly in the different lipids, hydrophobic mismatch does not seem to be the dominant factor causing the tilt. We suggest rather that the peptide itself has an inherently preferred tilted orientation, possibly related to peptide surface characteristics or the disposition of tryptophan indole anchors relative to the lipids, the peptide backbone, and the membrane/water interface. Additionally, the data allow us to define more precisely the local alanine geometry in this membrane-spanning alpha-helix.
Department of Chemistry and Biochemistry, University of Arkansas, Fayetteville, Arkansas 72701 USA. pvander@uark.edu
Patrick C A
PC
van der Wel
Erik
E
Strandberg
J Antoinette
JA
Killian
Roger E
RE
Koeppe
D000409:Alanine / Q000737:chemistry; D055592:Biophysical Phenomena; D001703:Biophysics; D002462:Cell Membrane / Q000502:physiology* / Q000648:ultrastructure; D008051:Lipid Bilayers; D009682:Magnetic Resonance Spectroscopy; D008956:Models, Chemical; D008958:Models, Molecular; D008962:Models, Theoretical; D010455:Peptides / Q000737:chemistry; D010713:Phosphatidylcholines / Q000737:chemistry; D017433:Protein Structure, Secondary; D014364:Tryptophan / Q000737:chemistry*
D008051:Lipid Bilayers; D010455:Peptides; D010713:Phosphatidylcholines; D014364:Tryptophan; C017251:1,2-oleoylphosphatidylcholine; D000409:Alanine