Fusion mechanism

Figure 7. A recently proposed HIV adsorption/fusion mechanism onto T cel I s CD4 receptor with coreceptor (chemokine, etc.), fol lowed by breaching the T-cell membrane by HIV glycoprotein gp41.

Analysis of SFV entry has thus shown that the virus binds to receptors on the cell surface and moves by lateral diffusion into coated pits to be internalized by coated vesicles. The endocytosed virus is delivered into endosomes. Here presumably, the viral envelope is activated by the low pH prevailing in this compartment to fuse with the vacuolar membrane. This results in the release of the viral nucleocapsid into the cytoplasm. During normal infection, the virus might not enter into lysosomes although SFV particles have been identified in this compartment using the large loads of virus needed to visualize the entry process by electron microscopy. Even if this were to happen normally, the viral nucleocapsid would escape destruction because of the rapidity of the fusion mechanism. 

The emission of a helium nucleus in the final stage regenerates the initial carbon-12. The latter thus plays the role of a catalyst. The overall result is the fusion of four protons into a helium nucleus. At high temperatures, this cycle dominates over the proton-proton chain. Indeed thermal agitation facilitates penetration of the relatively high electrical barrier between proton and carbon nucleus. Whatever hydrogen fusion mechanism is prevalent, the star s mass determines the rate at which it consumes its nuclear fuel, and hence also its lifetime. The higher its mass, the more quickly it bums. 

Kasson, P.M., Pande, V.S. Control of membrane fusion mechanism by lipid composition predictions from ensemble molecular dynamics. PLoS Comput. Biol. 2007, 3, e220. 

Schematic diagram showing the relative locations of nucleus, endoplasmic reticulum (ER), Golgi complex, trans-Golgi network, and plasma membrane. Glycoproteins synthesized in the lumen of the ER pass to the cis cisterna of the Golgi complex by a sequential membrane budding and fusion mechanism. The Golgi cisternae are classified into cis, medial, and trans in the order of increasing...

Siegel DP, Epand RM (1997) The mechanism of lamellar-to-inverted hexagonal phase transitions in phosphatidylethanolamine implications for membrane fusion mechanisms. Biophys J 73 3089-3111... 

Vignery A. Osteoclasts and giant cells macrophage-macrophage fusion mechanism. International Journal of Experimental Pathology 2000, 81, 291-304. 

Elegant studies have been carried out to investigate the structural and biochemical aspects of virus-cell fusion. Although influenza virus hemagglutinin and human immunodeficiency virus (HIV) gpl20 have been the best-studied models, numerous examples of this class I type fusion mechanism have been described. These experiments have shown that fusion is initiated by the formation of a trimeric coiled-coil helix adjacent to the fusion peptide on the virus exterior, the insertion of this fusion peptide into the host cell membrane, and the subsequent formation of a six-helix bundle (Skehel and Wiley, 1998). 

Membrane fusion is an essential process in the life of cells found in a variety of key extracellular and intracellular events, for example, exocytosis, vesicular transport, fertilization, neurosecretion, and viral infection (see Membrane fusion, mechanisms of). This process also is of intense biomedical interest, especially for drug delivery systems (see Drug delivery). 

The propensity of membranes to fuse correlates with the fraction of inverted phase-forming lipids conversely, membrane fusability is reduced with an increase of the lipid fraction that inhibits inverted phase formation. Substantial evidence suggests that the mechanism of lipid membrane fusion is related to the mechanism of lamellar/inverted phase transitions (23). The intermediates that form in membrane fusion seem to be identical to those that form during the transformations between lamellar, bicontinuous inverted cubic and inverted hexagonal lipid liquid-crystalline phases, and these transitions can be used successfully as a model for studying the lipid membrane fusion mechanism and kinetics. 

Membrane Trafficking Membrane Fusion, Mechanisms of Neurotransmitter Production and Storage Neurotransmitter Uptake and Degradation Neurotransmission, Chemical Events in Synaptic Chemistry... 

Membranes, Fluidity of Membrane Proteins, Properties of Membrane Fusion, Mechanisms of Lipid BUayers, Properties of Lipid Rafts Biosensors... 

Judice JK, Tom JY, Huang W et al (1997) Inhibition of HIV type 1 infectivity by constrained a-helical peptides implications for the viral fusion mechanism. Proc Natl Acad Sci USA 94 13426-13430... 

Reverse Osmosis Asymmetric membrane with homogeneous skin and microporous sub- or support structure Hydrostatic pressure 10-100 bar Solut ion-d if fusion mechanism, solubility, and dif-fusivity of individual components in the homogeneous polymer matrix determine separation characteristics. Concentration of microsolutes, such as salts, sugars, amino acids, etc., recovery of water from microbiological processes. 

The adhesion and fusion mechanisms between bilayers have also been studied with the SFA [M, 100]. Kuhl et al [17] found that solutions of short-chained polymers (PEG) could produce a short-range depletion attraction between lipid bilayers, which clearly depends on the polymer concentration (figure Bl. 20.11). This depletion attraction was found to induce a membrane fusion within 10 minutes that was observed, in real-time, using FECO fringes. There has been considerable progress in the preparation of fluid membranes to mimic natural conditions in the SFA [87], which promises even more exciting discoveries in biologically relevant areas. 

In order to improve the understanding of these systems, Kunieda and coworkers examined the thermotropic behavior of poly(oxyethylene) cholesteryl ethers with different chain lengths, ChFOn, mixed with water at a fixed concentration ( 25 wt%) [32]. This study focused on the different fusion mechanisms that were involved in the solid-liquid phase transition. The soUd-Uquid transition temperature for ChFOn as a function of n is shown in Figure 4.3 (for comparison, the transition temperature for polyethylene glycol is also shown). In both cases, the transition temperature decreased when the chain length was diminished. However, for the cholesterol surfactant, when n < 10, a birefringent phase appeared between... 

PA-6 (20-80)/PA-66 (80-20) Wayne extruder at 280 °C/various phosphite catalysts/Tm, heat of fusion, mechanical properties Khanna et al. 1983... 

Moore, J., Jameson, B., Weiss, R., and Sattentau, Q. (1993) The HIV-cell fusion reaction, in Viral Fusion Mechanisms (Bentz, J., ed.), CRC Press, Boca Raton, FL, pp. 233-289. 

J. Bentz, Viral Fusion Mechanisms, CRC Press, Boca Raton, 1993. 

Key words Amphipathic peptide -clathrin - liposome - membrane fusion - fusion mechanism... 

FIGURE 5.19 Role of cholesterol in the exocytosis of synaptic vesicles. Cholesterol constrains the conformation of v-SNARE proteins in such a way that their transmembrane domains adopt a parallel ("closed scissors") orientation. This particular conformation is required for the fusion process because it induces a fusion-compatible curvatiue of the s)fnaptic vesicle. In this case, the interaction between v-SNARE and t-SNARE proteins triggers the fusion mechanism (lower inset, 2). Without cholesterol, v-SNARE remains in an "open scissors" conformation (upper inset, 1), and the curvature of the vesicle is not appropriate for fusion. ... 

A very different scenario emerged in the case of simrd-taneous unimer exchange and fusion/fission. No quasi-equilibrium was observed and association proceeded quickly. Odd i-mers never prevailed and dimers turned into tetramers, then hexamers, octamers, and so on. At the beginning of the miceUization process, the micelle fusion mechanism was practically the only active one, until unimer expulsion from micelles became active. It is only toward the end of the process that unimer exchange became significant, in conjrmction with micelle fusion, particrdarly between rmequal micelles. 

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