Microviscosity of togavirus membranes studied by fluorescence depolarization: influence of envelope proteins and the host cell

Abstract

The microviscosities of the hydrophobic regions of the membranes of intact Semliki forest and Sindbis viruses grown on BHK-21 [baby hamster kidney] cells, of liposomes derived from the extracted viral lipids and of protease-treated virions were measured by fluorescence depolarization using the fluorescence probe 1,6-diphenyl-1,3,5-hexatriene. The intact virus membranes had a higher microviscosity than did virus-derived liposomes, indicating that viral envelope proteins contribute to microviscosity. Protease-treated virus, devoid of protruding spikes but with residual lipophilic peptide tails, had a microviscosity more similar to that of the intact virus than to that of protein-free liposomes. Sindbis virus grown in BHK-21 cells at 37.degree. C had a much higher microviscosity than did Sindbis virus grown on Aedes albopictus cells at 22.degree. C. Sindbis virus grown in A. albopictus and BHK-21 cells also gave higher microviscosity values than did the intact host cells. The virion proteins and the cellular lipids selected during viral growth and maturation may contribute to the increased microviscosity of togavirus membranes.