Viral fusion proteins

The viral fusion systems provide a unique opportunity to study membrane fusion at the molecular level. It would be surprising if the mechanism of spike protein-mediated fusion did not have features in common with the mechanisms involved in the fusion reactions occurring during membrane vesicle traffic in the cell. It may even be that the viral fusion proteins have evolved from cellular fusion proteins. The trigger for cellular fusion would of course be different and other proteins would be needed to specify which membranes are to fuse together. 

Enfuvirtide is a peptide that binds to the viral fusion protein in such a manner as to prevent the necessary change in conformation. It is a reserve drug. 

Virosomes are liposomes containing viral fusion proteins that allow efficient entering into cells fusion with endosome membranes. Viral fusion proteins become activated in the low pH environment in the endosome to release its contents into the cytosol. Hepatitis A and influenza vaccines constructed on virosomes elicited fewer local adverse reactions than did their classic counterparts and displayed enhanced immunogenicity. Virosome-formulated influenza vaccine has also been shown to be safe and immunogenic when administered by the intranasal route. Other studies have suggested that immunopotentiating reconstituted influenza virosomes can be a suitable delivery system for synthetic... 

One criterion for a bona fide membrane-fusion protein is that membrane fusion can be reconstituted by transfection of the candidate fusion protein into nonfusing cells or by reconstitution into lipid vesicles (White, 1990 White, 1992 White and Blobel, 1989). Transfection of meltrin a into fibroblasts did not lead to an increase in cell fusion (Yagami-Hiromasa et al., 1995). Clearly, failure to reconstitute fusion does not rule out a role in fusion because the cellular fusion machinery may be more complex than viral fusion proteins. Muscle cells might contain other proteins that are required for meltrin a to promote membrane fusion but that are not expressed or active in fibroblasts. Ultimately, the identity of a bona fide cell-cell fusion protein or protein machine will only be determined by reconstituting membrane fusion with defined components. In the interim, it will be important to more accurately understand the roles of meltrin a and fertilin in the cascade of steps that result in membrane fusion and thereby perhaps distinguish between a direct and indirect role in fusion. 

Hughson, F.M. (1995). Structural characterization of viral fusion proteins. Cutr. Biol. 5 265-274. Hyne, R.V. and Garbers, D.L. (1979a). Calcium-dependent increase in adenosine 3, 5 - monophosphate and induction of the acrosome reaction in guinea pig spermatozoa. Proc. Natl. Acad. Sci. 76 5699-5703. 

Debnath AK (2006) Prospects and strategies for the discovery and development of small-molecule inhibitors of six-helix bundle formation in class 1 viral fusion proteins. Curr Opin Investig Drugs 7 118-127... 

Figure 7.1-3. The ideal synthetic (nonviral) gene delivery vector. After dense DNA packaging is accomplished (e.g., by protamine sulfate), the surface of synthetic particles (which is usually positively charged) needs to be shielded (e.g., by poly (ethylene-glycol) [PEG]) so that they do not attach to blood elements or to each other and, therefore, have an extended circulating plasma half-life (1) (passive targeting to leaky vessels ). The surface of the particles will contain specific ligands for active targeting to selected cells/ tissues (2). By engineering viral fusion proteins to the particle coat, cell entry is facilitated...

Hong et al. discussed recent advances in using SSNMR to study K and H" " channels, Ca + pumps, G protein-coupled receptors, bacterial outer membrane proteins, and viral fusion proteins to elucidate their mechanisms of action at the membrane. Shi and Ladizhansky underlined that SSNMR has become a prominent method for the characterization of insoluble proteins and protein aggregates such as amyloid fibrils and membrane-lipid complexes. Im et al. developed SSNMR ensemble dynamics (SSNMR-ED) using multiple conformer models, which generates an ensemble of structures that satisfies the experimental observables without any fitting parameters. 

Other viral targets Attachment proteins Fusion proteins Disassembly/Uncoating... 

Kobinger GP, Borsetti A, Nie Z, Mercier J, Daniel N, Gotthnger HG, Cohen A (1998) Virion-targeted viral inactivation of human immunodeficiency virus type 1 by using Vpr fusion proteins. J Virol 72 5441-5448... 

Protein kinase B, or Akt, was discovered as the product of an oncogene of the acutely transforming retrovirus AKT8, causing T-cell lymphomas in mice. It encodes a fusion product of a cellular serine/threonine protein kinase and the viral structural protein Gag. This kinase is similar to both protein kinase Ce (PKCe 73% identity to the catalytic domain) and protein kinase A (PKA 68%). It differs from other protein kinases in that it contains a pleckstrin homology (PH) domain, which allows it to bind to polyphosphoinositide head groups (and also to G-protein fly subunits). To date, three subtypes have been identified a, (3, and y, all of which show a broad tissue distribution. It... 

In the second research strategy, plant viruses have been utilized as pliable genetic platforms for protein expression. Three formats have been developed, and the one that has undergone the most extensive evaluation is the display of epitopes on the surface of the virus as fusions with the viral coat protein. This epitope-display system... 

Kundu et al.64 used MEKC conditions to assess the purity of two recombinant proteins a cytomegalovirus-CMP-KDO synthetase fusion protein expressed in E. coli and a hepatitis C viral protein expressed in CHO cells. Proteins were prepared in a 10-mM Tris-1% SDS buffer (pH 8.5) and analyzed in a 10-mM borate-100-mM SDS buffer (pH 9.5) in uncoated capillaries. The level of impurities, which varied with the method of protein production, agreed within 5% with results obtained by densitometric scanning of SDS-PAGE gels of the same materials. 

Studies of the alphavirus life cycle have revealed how heavily the virus relies on cellular processes for replication. The paucity of functions that seem unique to the virus is striking. The binding of the virus to the cell surface and the fusion of its membrane intracellularly depend on the viral spike glycoproteins. RNA-dependent RNA polymerases specific for the virus catalyze the replication of the viral RNA. Exit from the cell requires the interaction of the viral spike proteins with the viral capsid... 

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