The dynamics of membrane-spanning peptides have a strong affect on the solid-state NMR observables. We present a combined analysis of 2H-alanine quadrupolar splittings together with 15N/ 1H dipolar couplings and 15N chemical shifts, using two models to treat the dynamics, for the systematic evaluation of transmembrane peptides based on the GWALP23 sequence (acetyl-GGALW(LA) 6LWLAGA- amide). The results indicate that derivatives of GWALP23 incorporating diverse guest residues adopt a range of apparent tilt angles that span 5°-35° in lipid bilayer membranes. By comparing individual and combined analyses of specifically 2H- or 15N-labeled peptides incorporated in magnetically or mechanically aligned lipid bilayers, we examine the influence of data-set size/identity, and of explicitly modeled dynamics, on the deduced average orientations of the peptides. We conclude that peptides with small apparent tilt values (<∼10°) can be fitted by extensive families of solutions, which can be narrowed by incorporating additional 15N as well as 2H restraints. Conversely, peptides exhibiting larger tilt angles display more narrow distributions of tilt and rotation that can be fitted using smaller sets of experimental constraints or even with 2H or 15N data alone. Importantly, for peptides that tilt significantly more than 10° from the bilayer-normal, the contribution from rigid body dynamics can be approximated by a principal order parameter.
Bibliographical noteFunding Information:
This work was supported in part by grants from the National Science Foundation (MCB-0841227) and the Arkansas Biosciences Institute. The peptide and 2 H NMR facilities were supported by National Institutes of Health grants RR31154 and RR16460. Part of the research was performed at the Biotechnology Research Center for NMR Molecular Imaging of Proteins at the University of California, San Diego, which is supported by National Institutes of Health grant P41EB003031.