Je. Wellington et al., N-TERMINAL SEQUENCE-ANALYSIS OF EQUINE HERPESVIRUS-1 GLYCOPROTEIN-D AND GLYCOPROTEIN-B AND EVIDENCE FOR INTERNAL CLEAVAGE OF THE GENE-71 PRODUCT, Journal of General Virology, 77, 1996, pp. 75-82
Signal cleavage sites of equine herpesvirus 1 (EHV-1) glycoproteins D
and B (gD and gB) and an endoproteolytic cleavage site of EHV-1 gB wer
e determined by N-terminal amino acid sequencing and compared with kno
wn cleavage sites of homologues in other herpesviruses. Signal cleavag
e of EHV-1 go occurred between Arg(35) and Ala(36) in a region of basi
c amino acids resembling the endoproteolytic cleavage sites of viral g
lycoproteins, nine amino acids downstream of the predicted site, while
EHV-1 gB was cleaved as predicted between Ala(85) and Val(86). Endopr
oteolytic cleavage of EHV-1 gB occurred between Arg(548) and Ala(549),
28 amino acids downstream of the cleavage site predicted from conserv
ed sequences of other herpesvirus gB homologues. One interpretation of
these data is that EHV-1 gB is cleaved internally at both sites, a po
ssibility which was supported by the apparent molecular masses of the
unglycosylated gB subunits produced in the presence of tunicamycin. Th
is double cleavage would release a stretch of amino acids which is not
present in sequenced gB molecules of other herpesviruses. Experiments
with glycosylation inhibitors indicated that cleavage of EHV-1 gB can
occur in the absence of glycosylation. N-terminal sequencing also det
ermined that a 42 kDa EHV-1 glycoprotein was a product of internal cle
avage of the protein encoded by gene 71. Staggered endoproteolytic cle
avage after adjacent arginine residues 506 and 507 separates the 42 kD
a C-terminal subunit containing all the cysteine residues from the ser
ine and threonine rich N-terminal region.