13-C nuclear magnetic resonance studies on the lipid organization in enveloped virions (vesicular stomatitis virus)

13-C nuclear magnetic resonance (NMR) studies are described regarding the lipid organization in the envelope of the vesicular stomatitis virion. The fatty acid chains (oleic acid) and the choline moiety of the 3-sn-phosphatidylcholine and spingomyelin have been labeled specifically with 13-C by growing the virions in prelabeled host cells (BHK 21 cells). The results suggest that 130C NMR spectroscopy is a very feasible method for the study of natural membranes provided the isotope is highly enriched in specific positions and incorporated biochemically. Spin-lattice relaxation (T1) measurements of particular C atoms have been carried out with whole virions, with virions deprived of their surface projections by trypsinization but unaltered in their shape and size, and with liposomes prepared from the total lipid mixture of the envelope in order to get insight into the molecular structure of this model membrane. The mobility of the central part of 11-13-C-labeled oleic acid incorporated into the ester and amide lipids and the choline group of 3-sn-phosphatidylcholine and sphingomyelin is very restricted as indicated by their short T1 times. It is concluded from the data presented here that the high cholesterol content (cholesterol/P: 0.7) of the envelope lipid phase is responsible for the rather rigidly packed envelope structure. The mode and extent of the interactions between lipids and glycoprotein surface projections are subjects for further study.