Protein Modulation of Liposome Fusion

Abstract

Membranes provide the barrier of cellular individuality or intracellular compartmentation. Individuality or compartmentation is unlikely to be traversed except in A. well-regulated biological process, membrane fusion. To understand the fundamental mechanism of membrane fusion, simple membrane systems have been studied extensively (reviewed by Papahadjopoulos et al, 1979; Nir et al, 1983; Düzgünes, 1985). Information obtained from model membranes has been useful not only for defining the role of fusion triggers or modulators, but also for determining the fusion susceptibility of individual components of membranes. However, fusion requirements for these simple systems are often far from those known to be required for biological fusion. For example, fusion between isolated secretory vesicles occurs at much lower Ca²⁺concentrations than those required for fusion of liposomes made from the extracted lipids of the secretory vesicles (Gratzl et al, 1980; Ekerdt et al, 1981). A. simple explanation for this discrepancy in Ca²⁺threshold is that other factors are involved in the sensitivity for Ca²⁺in the fusion event. Among these factors, protein is considered A. likely candidate. Therefore, protein-facilitated fusion of liposomes is an important step toward the reconstitution of natural membrane fusion.