CONFORMATION OF SULFOQUINOVOSYLDIACYLGLYCEROL BOUND TO A MAGNETICALLYORIENTED MEMBRANE SYSTEM

The conformation of uniformly C-13-labeled sulfoquinovosyldiacylglycer ol (SQDG) is studied in both membrane and solution environments using NMR spectroscopy, Analysis in a membrane-like environment is based on the measurement of dipolar interactions between C-13-C-13 and H-1-C-13 spin pairs and on the measurement of C-13 chemical shift anisotropy o ffsets, which appear in magnetically oriented phospholipid-based membr ane fragments, Potential energy maps for glycosidic torsions, phi, psi , and theta 1, are calculated with a membrane interaction energy and a re used in the interpretation of experimental data. The membrane-bound description for SQDG is most consistent with a set of low-energy conf ormations that extends the headgroup of SQDG away from the membrane su rface. Analysis of the conformation of SQDG in CD3OD solution is based on measured (3)J(CH) scalar couplings. The description of the solutio n conformation is modeled as a mixture of low-energy conformers predic ted in the absence of a membrane interaction term and involves more ex tensive motional averaging than the model for SQDG embedded in the lip id matrix.