Sendai virus membrane fusion: time course and effect of temperature, pH, calcium, and receptor concentration

Abstract

The conditions that optimize Sendai virus membrane fusion with liposomes have been studied. No fusion occurs in the absence of ganglioside receptors. Maximum fusion occurs when the molar ratio of ganglioside GD1a to phospholipid is .gtoreq. 0.02. The amount of fusion at 37.degree. C increases with time up to at least 6.5 h. The rate of fusion increases from the lowest temperature tested, 10.degree. C, to 40.degree. C. Above 43.degree. C the amount of fusion decreases because of thermal inactivation of the viral proteins. There is a broad pH maximum between pH 7.5 and 9.0. At both ends of the pH range the amount of fusion increases and exceeds that found in the physiologic pH range. Neither EDTA nor Ca2+ changes the amount of membrane fusion. The optimal conditions for membrane fusion of Sendai virus membranes with liposomes are the same as the optimal conditions for fusion with host cells and with red blood cells. Since the liposomes contain no proteins, the optimal conditions for Sendai virus membrane fusion must be determined by the viral proteins and be mostly independent of the nature or presence of the host proteins.