CONFORMATION AND DYNAMICS OF MEMBRANE-BOUND DIGALACTOSYLDIACYLGLYCEROL

The conformation and dynamics of a uniformly C-13-labeled glycolipid, digalactosyldiacylglycerol (DGDG), is studied in a membrane environmen t using NMR spectroscopy. Dipolar couplings and C-13 chemical shift an isotropy offsets which appear in magnetically oriented phospholipid-ba sed membrane fragments are used to derive a detailed description of th e conformation and amplitudes of motion. C-13 relaxation rates (T-1, T -2, and NOE) were then measured for C-13 sites in DGDG anchored to iso tropically tumbling phospholipid bilayers. Using a Lipari and Szabo ty pe approach, a nonlinear least squares fit of relaxation rates to moti onal parameters yielded rates and amplitudes of internal motions for t he first and terminal sugar of the,glycolipid head group. Generalized order parameters extracted from relaxation data show good agreement wi th order parameters used to fit dipolar couplings. The combined model is analyzed in terms of potential energy maps generated using a versio n of AMBER modified to include a membrane interaction energy term. The experimental conformational preferences of the terminal alpha(1-6) li nkage in DGDG agree quite well with predictions based on these calcula tions.