Bovine herpesvirus 1 glycoprotein M forms a disulfide-linked heterodimer with the U(L)49.5 protein.

Nine glycoproteins (gB, gC, gD, gE, gG, gH, gI, gK, and gL) have been identified in bovine herpesvirus 1 (BHV-1). gM has been identified in many other alpha-, beta-, and gammaherpesviruses, in which it appears to play a role in membrane penetration and cell-to-cell fusion. We sought to express BHV-1 open reading frame U(L)10, which encodes gM, and specifically identify the glycoprotein. We corrected a frameshift error in the published sequence and used the corrected sequence to design coterminal peptides from the C terminus. These were expressed as glutathione S-transferase fusion proteins in Escherichia coli. The fusion protein containing the 63 C-terminal amino acids from the corrected gM sequence engendered antibodies that immunoprecipitated a 30-kDa protein from in vitro translation reactions programmed with the U(L)10 gene. Proteins immunoprecipitated by this antibody from virus-infected cells ran at 36 and 43 kDa in reducing sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) and 43 and 48 kDa in nonreducing SDS-PAGE. Only the larger of the pair was present in virions. A 7-kDa protein was released from gM by reducing agents. The 7-kDa protein was not recognized in Western blots probed with the anti-gM antibody but reacted specifically with antibodies prepared against BHV-1 U(L)49.5, previously reported to be a 9-kDa protein associated with an unidentified 39-kDa protein (X. Liang, B. Chow, C. Raggo, and L. A. Babiuk, J. Virol. 70:1448-1454, 1996). This is the first report of a small protein covalently bound to any herpesvirus gM. Similar patterns of hydrophobic domains and cysteines in all known gM and U(L)49.5 homologs suggest that these two proteins may be linked by disulfide bonds in all herpesviruses.