The fusion-related properties of segments p9, p3, p4, and p9 + p2 surrounding the p2
phospholipid-binding domain of the
protein G (pG) of the salmonid rhabdovirus of
viral hemorrhagic septicemia (VHS) (Nuñez, E., Fernandez, A. M., Estepa, A., Gonzalez-Ros, J. M., Gavilanes, F., and Coll, J. M. (1998) Virology 243, 322-330; Estepa, A., and Coll, J. M. (1996) Virology 216, 60-70), have been studied at neutral and fusion (low) pH values by using its derived
peptides. Cell-to-cell fusion, translocation of
phosphatidylserine, and inhibition of fusion of pG-transfected cells defined the p9 + p2 (fragment 11, sequence 56-110) as a fragment with higher specific activity for anionic
phospholipid aggregation than the previously reported p2. While fragment 11, p2, and p3 showed interactions with anionic
phospholipids, p9 and p4 showed no interactions with any
phospholipids. When added to a cell monolayer model at low pH, fragment 11 induced pH-dependent cell-to-cell fusion and translocated
phosphatidylserine from the inner to the outer leaflet of the membrane. At low pH and in the presence of anionic
phospholipids, fragment 11 showed more than 80% beta-sheet conformation (IR and CD spectroscopies). Finally, anti-fragment 11
antibodies inhibited low pH-dependent pG-transfected cell-to-cell fusion. All of the data support the conclusion that fragment 11 is a primary determinant of some of the viral cell fusion events in VHSV.