1.G.15. The Autographa californica Nuclear Polyhedrosis Virus Major Envelope Glycoprotein GP64 (GP64) Family
The envelope glycoprotein, GP64, of the baculovirus Autographa californica multicapsid nucleopolyhedrovirus (AcMNPV) is a class III viral fusion protein that mediates pH-triggered membrane fusion during virus entry. Viral fusion glycoproteins from many viruses contain a short region in the ectodomain and near the transmembrane domain, referred to as the pre-transmembrane (PTM) domain. In some cases, the PTM domain is rich in aromatic amino acids and plays an important role in membrane fusion. Although the 23-amino-acid (aa) PTM domain of AcMNPV GP64 lacks aromatic residues, it plays a role in membrane fusion. Li and Blissard 2009 generated point mutations in the GP64 PTM domain, focusing on amino acid positions conserved between baculovirus GP64 and thogotovirus GP75 proteins, as well as hydrophobic and charged amino acids. For each PTM-modified construct, trimerization, cell surface localization, membrane merger, pore formation and membrane fusion activity were examined. Eight non clustered residues important for membrane fusion activity were identified. While charged residues were not critical, three hydrophobic amino acids (L465, L476, and L480) played a role in membrane fusion and appeared to be involved in formation of the fusion pore. Several conserved residues (T463, G460, G462, and G474) were not required for membrane fusion but were important for budding and viral infectivity (Li and Blissard 2009).