A comparison of the mobilities and thermal transitions of retrovirus lipid envelopes and host cell plasma membranes by electron spin resonance spectroscopy.

The lipid bilayers of several type-C retroviruses and selected host cells were spin labeled with 5-doxyl stearic acid, and intact viruses and cells were subjected to electron spin resonance spectroscopy in order to measure lipid mobility. Thermal transition profiles generated for four different retroviruses were dissimilar; differences in the values of the hyperfine splitting constant 2T parallel and in the positions of thermal break points reflect variations in mobility which can be correlated with the phospholipid/cholesterol molar ratios of the viral envelopes. Moreover, removal of virion surface projections by protease digestion altered the mobility of the envelope and in the positions of thermal break points, but the effect observed depended upon the particular retrovirus examined. Studies on retrovirus-infected and uninfected host cells have revealed that persistent virus infection can elicit changes in host plasma membrane mobility and in the positions of thermal break points, the direction and magnitude of which are highly dependent upon the particular retrovirus-host cell system under consideration.