Pepscan mapping and fusion-related properties of the major phosphatidylserine-binding domain of the glycoprotein of viral hemorrhagic septicemia virus, a salmonid rhabdovirus.

The binding of labeled phosphatidylserine (PS) to a collection of synthetic 15-mer peptides covering full-length glycoprotein G (G) of viral hemorrhagic septicemia virus (VHSV), a salmonid rhabdovirus, showed three dominant overlapping reactive peptides. This major PS-binding region was contained in a 28-mer peptide (p2; aa 82-109) with consecutive hydrophobic amino acid a-d heptad repeats (putative amphipathic alpha-helix) and 2 carboxy-terminal arginines. This 28-mer peptide showed a 10-fold higher apparent specific activity for PS binding than the 15-mer peptides. Binding to PS was also detected with virion-purified protein G but was not detected with other viral proteins. The highest apparent specific activity for PS binding was found with purified VHSV particles by both solid-phase and liquid assays. In contrast to the pH-independent PS binding to peptide p2, binding to virions was optimal at pH 5.6. PS binding to purified VHSV was greatly reduced by protease or detergent treatments that removed protein G, by treatment at pH 7.6, or by anti-p2 mouse antibodies at pH 5.6. The PS-binding region seems to be related to viral-host cell fusion since anti-p2 mouse antibodies inhibited VHSV-infected cell to cell fusion (fusion from within) and the pH profile of the VHSV-infected cell to cell fusion was similar to the pH profile of PS binding to VHSV. Comparative analysis showed that sequences similar to the major PS-binding domain of VHSV were also present in other fish rhabdoviruses and in rabies and vesicular stomatitis viruses.