Equine herpesvirus-4 glycoprotein G is secreted as a disulphide-linked homodimer and is present as two homodimeric species in the virion

Glycoprotein G (gG) homologues have been found in most alphaherpesviruses although little is known about their structure or function. In this study, three species of equine herpesvirus-4 (EHV-4) gG were identified: a full-length 68 kDa virion-associated species (gGV(L)), a 12 kDa virion-associated species (gGV(S)) and a 60 kDa secreted species (gGS), detected in the medium of infected cells. gGS and gGV(S) appear to be proteolytic cleavage products of gGV(L) and correspond to the N- and C-terminal regions, respectively. It was shown that gGS and gGV(L) are similarly glycosylated possessing mostly N-linked complex-type carbohydrate side chains. Western blots of proteins separated under nonreducing conditions established that gGS is secreted as a 120 kDa glycoprotein while the virion-associated species, gGV(L) and gGV(S), are present in the virion as 140 and 20 kDa proteins, respectively. As gGS and gGV(L) do not appear to associate stably with other viral proteins, it is most likely that each species exists as a disulphide-linked homodimer. Pulse-chase experiments indicated that gGV(L) is rapidly assembled as a homodimer prior to both carbohydrate side-chain maturation in the Golgi and proteolytic cleavage. Proteolytic cleavage of full-length gG occurs during or immediately after passage through the Golgi. Secreted and virion-associated species of gG were identified in the closely related virus EHV-1 and were of similar molecular masses to the corresponding EHV-4 gG species.