Cleavage of Epstein-Barr virus glycoprotein B is required for full function in cell-cell fusion with both epithelial and B cells.

Glycoprotein B (gB) homologues within the herpesvirus family display high sequence conservation, and a number of gB homologues contain a cleavage motif R-X-K/R-R recognized by the cellular protease furin. Epstein-Barr virus (EBV) gB contains this motif and cleaved gB is found in EBV virions. To determine the functional significance of this cleavage motif in EBV gB, a deletion mutant (gB Deltafurin) was created lacking the motif. This cleavage mutant was expressed well in cell culture but was not cleaved. Experiments examining gB Deltafurin in a cell-fusion assay revealed that fusion was reduced by 52 % in epithelial and 28 % in B cells when compared with wild-type EBV gB. This decrease in cell-cell fusion is similar to that observed with multiple alphaherpesvirus gB cleavage mutants and supports a conserved function for cleaved gB.