| dc.description | Avian and Nelson Bay reoviruses are rare examples of nonenveloped viruses that encode a membrane fusion protein (p10). P10 is an integral membrane, type I, surface localized nonstructural protein. The life cycle of reoviruses and the unique characteristics of p10 suggest that unlike other biological membrane fusion proteins, p10-induced membrane fusion may not require regulation, specificity, rapidity or efficiency. Liposome fusion assays, structural studies, and mutational analysis show that p10 contains an internal fusion peptide with a beta-strand rich disulfide-bonded loop structure. Similar to the enveloped virus fusion proteins, the fusion peptide is proposed to promote fusion through destabilizing interactions with the target membrane. The p10 fusion peptide is directly responsible for rapid proteasome-dependent intracellular degradation of p10 suggesting that it is exposed upon p10 expression. The small size of the p10 ectodomain, the absence of heptad repeats shared by most enveloped virus- and intracellular vesicle fusion proteins, and the exposure of the p10 fusion peptide support that regulated conformational changes commonly associated with the activation of other biological fusion proteins are not necessary for p10. Mutational analysis shows that the glycine-rich transmembrane domain, intracellular palmitoylated cysteines and basic region are directly involved in the fusion process. That alterations to donor bilayer lipid packing favor membrane merger is a newly emerging concept. P10 also appears to exist as a monomer unlike all other oligomeric biological membrane fusion proteins. To explain the unique characteristics of p10, we propose that p10 is expressed in the fusion competent conformation. Our analysis of p10 may allow the minimal determinants for membrane fusion to be deciphered from auxiliary regulatory components found in other biological membrane fusion proteins. | en_US |
