Virosomes constructed from lipid and purified Friend leukaemia virus glycoprotein.

Liposomes were loaded by a dialysis technique with purified envelope glycopolypeptide, gp85, of the Friend murine leukaemia virus (F-MuLV). The gp85 liposomes prepared from cellular lipid had a buoyant density of 1.05 g/ml and an apparent diameter of 50 to 300 nm. The gp85 was not simply entrapped by liposomes nor adsorbed non-specifically to their outer surface. Experiments with radioactively labelled protein, electron microscopic examinations, protease treatment and concanavalin A binding showed that gp85 is anchored in the liposomal membrane and oriented asymmetrically as in the virus envelope. Moreover, gp85-covered liposomes displayed some functions of the intact F-MuLV envelope, such as absorption of antibodies to gp70 and haemagglutination after enzyme treatment. To some extent, these lipid vesicles appeared to be reconstituted F-MuLV envelopes and thus, by analogy to other systems, were named retrovirosomes.