An α-helical domain within the carboxyl terminus of herpes simplex virus type 1 (HSV-1) glycoprotein B (gB) is associated with cell fusion and resistance to heparin inhibition of cell fusion

Previous studies from our laboratory indicated that a 28-amino-acid carboxyl-terminal truncation of gB caused extensive virus-induced cell fusion (Baghian et al., 1993, J Virol 67, 2396-2401). We tested the ability of additional truncations and mutations within gB to cause cell fusion in the recently established virus-free cell fusion assay (Turner et al., 1998, J.. Virol. 72, 873-875). Deletion of the carboxyl-terminal 28 amino acids of gB (gB Delta 28), which removed part of the predicted alpha -helical structure H17b, caused extensive cell fusion. A gB truncation specified by gB Delta 36, which removed the entire H17b domain, caused as much cell fusion as the gB Delta 28 truncation. Similarly, gB(A874P) containing a substitution of an Ala with Pro within H17b caused cell fusion. Heparin, a gB-specific inhibitor of virus-induced cell fusion, inhibited both wild-type gB and gB(syn3)-mediated cell fusion. In contrast, fusion of cells transfected with gB(Delta 28), gB(Delta 36), or gB(A874P) was resistant to heparin inhibition of cell fusion. We concluded the following: (1) The predicted alpha -helical structure of H17b within the carboxyl terminus of gB is involved in both virus-induced and virus-free cell fusion. (2) Heparin is a specific inhibitor of gB-mediated fusion in bath systems. (3) Resistance to heparin inhibition of gB-mediated cell fusion is associated with the predicted a-helical structure H17b within the carboxyl terminus of gB. (C) 2001 Academic Press.