Showing papers on "Interbilayer forces in membrane fusion published in 1995"

Lipids in biological membrane fusion.

Abstract: The results reviewed suggest that membrane fusion in diverse biological fusion reactions involves formation of some specific intermediates: stalks and pores. Energy of these intermediates and, consequently, the rate and extent of fusion depend on the propensity of the corresponding monolayers of membranes to bend in the required directions. Proteins and peptides can control the bending energy of membrane monolayers in a number of ways. Monolayer lipid composition may be altered by different phospholipases [50, 85, 90], flipases and translocases [4, 50]. Proteins and peptides can change monolayer spontaneous curvature or hydrophobic void energy by direct interaction with membrane lipids [20, 32, 111]. Proteins may also provide some barriers for lipid diffusion in the plane of the monolayer [83, 141]. If diffusion of lipids at some specific membrane sites (e.g., in the vicinity of fusion protein) is somehow hindered, the energy of the bent fusion intermediates would reflect the elastic properties of these particular sites rather than the spontaneous curvature of the whole monolayers. Proteins may deform membranes while bringing them locally into close contact. The alteration of the geometric (external) curvature will certainly change the elastic energy of the initial state and, thus affect the energetic barriers of the formation of the intermediates [143]. In addition, the area and the energy of the stalk can be reduced by preliminary bending of the contacting membranes [111]. The possible effects of proteins and polymers on local elastic properties and local shapes of the membranes have been recently analyzed [22, 39, 45, 63]. These studies may provide a good basis for future development of theoretical models of protein-mediated fusion. Various models for biological fusion have been presented as hypothetical sequences of intermediate conformations of proteins, with membrane lipids just covering the empty spaces between the proteins. Although the results discussed above do not allow us to draw an allexplaining cartoon of the fusion mechanism, they do indicate which properties of membrane lipid bilayers (if modified by fusion proteins) would get these bilayers to fuse. In addition, these data suggest a specific geometry to bent fusion intermediates (stalks and pores) and imply a contribution by lipids to the energy of these intermediates. We think that the synthesis of rapidly developing structural information on fusion proteins with the analysis of the physics of membrane rearrangement may soon yield a real understanding of the fascinating and fundamental phenomenon of membrane fusion.

Temperature-favoured assembly of collagen is driven by hydrophilic not hydrophobic interactions.

Abstract: It has become almost axiomatic that protein folding and assembly are dominated by the hydrophobic effect. The contributions from this, and other, hydrophilic interactions can now be better distinguished by direct measurement of forces between proteins. Here we report the measurement of forces between triple helices of type I collagen at different temperatures, pH and solute concentrations. We separate repulsive and attractive components of the net force and analyze the origin of the attraction responsible for the collagen self-assembly. In this case the role of the hydrophobic effect appears to be negligible. Instead, water-mediated hydrogen bonding between polar residues is the most consistent explanation.

Cation-Induced Vesicle Fusion Modulated by Polymers and Proteins

Abstract: Publisher Summary This chapter has its focus on applications of phospholipid vesicles for the elucidation of molecular mechanisms of membrane fusion. Rather than presenting a complete review of work on vesicle fusion, basic biophysical concepts are demonstrated for fusion processes induced by cations, polymers and cation-binding proteins. Biological fusion processes are briefly reviewed to define the components involved in fusion processes. Fluorescence techniques that are frequently used to monitor the fusion are described. Before the fusion of vesicles is discussed, the aggregation of vesicles is considered with emphasis on the realization of a close approach of the membranes, recognized as a requirement for fusion. Some current models of vesicle fusion are discussed in the chapter. The basic finding of these studies was that membrane surface hydrophobicity is one of the important factors contributing to membrane fusion. A hydrophobic interaction of membranes results when hydrophobic groups of the membrane are exposed to water. As discussed in the chapter such hydrophobic areas are formed by binding of cations to bilayer surfaces, local packing strains induced by osmotic stresses, inhomogeneous binding of cations and penetration of proteins into the bilayer.