| Summary: | <p>Abstract</p> <p>Background</p> <p>Members of the <it>Baculoviridae </it>encode two types of proteins that mediate virus:cell membrane fusion and penetration into the host cell. Alignments of primary amino acid sequences indicate that baculovirus fusion proteins of group I nucleopolyhedroviruses (NPV) form the GP64 superfamily. The structure of these viral penetrenes has not been determined. The GP64 superfamily includes the glycoprotein (GP) encoded by members of the <it>Thogotovirus </it>genus of the <it>Orthomyxoviridae</it>. The entry proteins of other baculoviruses, group II NPV and granuloviruses, are class I penetrenes.</p> <p>Results</p> <p>Class III penetrenes encoded by members of the <it>Rhabdoviridae </it>and <it>Herpesviridae </it>have an internal fusion domain comprised of beta sheets, other beta sheet domains, an extended alpha helical domain, a membrane proximal stem domain and a carboxyl terminal anchor. Similar sequences and structural/functional motifs that characterize class III penetrenes are located collinearly in GP64 of group I baculoviruses and related glycoproteins encoded by thogotoviruses. Structural models based on a prototypic class III penetrene, vesicular stomatitis virus glycoprotein (VSV G), were established for Thogoto virus (THOV) GP and <it>Autographa california </it>multiple NPV (AcMNPV) GP64 demonstrating feasible cysteine linkages. Glycosylation sites in THOV GP and AcMNPV GP64 appear in similar model locations to the two glycosylation sites of VSV G.</p> <p>Conclusion</p> <p>These results suggest that proteins in the GP64 superfamily are class III penetrenes.</p>
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