EQUINE HERPESVIRUS-4 GLYCOPROTEIN-G IS SECRETED AS A DISULFIDE-LINKEDHOMODIMER AND IS PRESENT AS 2 HOMODIMERIC SPECIES IN THE VIRION

Glycoprotein G (gG) homologues have been found in most alphaherpesviru ses although little is known about their structure or function. In thi s study, three species of equine herpesvirus-4 (EHV-4) gG were identif ied: 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- an d C-terminal regions, respectively. It was shown that gGS and gGV(L) a re similarly glycosylated possessing mostly N-linked complex-type carb ohydrate side chains. Western blots of proteins separated under nonred ucing conditions established that gGS is secreted as a 120 kDa glycopr otein while the virion-associated species, gGV(L) and gGV(S), are pres ent 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, i t is most likely that each species exists as a disulphide-linked homod imer. Pulse-chase experiments indicated that gGV(L) is rapidly assembl ed as a homodimer prior to both carbohydrate side-chain maturation in the Golgi and proteolytic cleavage. Proteolytic cleavage of full-lengt h gG occurs during or immediately after passage through the Golgi. Sec reted and virion-associated species of gG were identified in the close ly related virus EHV-1 and were of similar molecular masses to the cor responding EHV-4 gG species.