Juxta-terminal Helix Unwinding as a Stabilizing Factor to Modulate the Dynamics of Transmembrane Helices.

Transmembrane helices of integral membrane proteins often are flanked by interfacial aromatic residues that can serve as anchors to aid the stabilization of a tilted transmembrane orientation. Yet, physical factors that govern the orientation or dynamic averaging of individual transmembrane helices are not well understood and have not been adequately explained. Using solid-state (2) H NMR spectroscopy to examine lipid bilayer-incorporated model peptides of the GWALP23 (acetyl-GGALW(LA)6 LWLAGA-amide) family, we observed substantial unwinding at the terminals of several tilted helices spanning the membranes of DLPC, DMPC, or DOPC lipid bilayers. The fraying of helix ends might be vital for defining the dynamics and orientations of transmembrane helices in lipid bilayer membranes.