Synthesis and Processing of the Equine Herpesvirus 1 Glycoprotein M

Abstract

In a previous report, the function of the equine herpesvirus 1 (EHV-1) glycoprotein M (gM) homolog was investigated. It was shown that EHV-1 gM is involved in both virus entry and direct cell-to-cell spread of infection (N. Osterriederet al., J. Virol.70, 4110–4115, 1996). In this study, experiments were conducted to analyze the synthesis, posttranslational processing, and the putative ion channel function of EHV-1 gM. It was demonstrated that EHV-1 gM is synthesized as anMr44,000 polypeptide, which is cotranslationally N-glycosylated to anMr46,000–48,000 glycoprotein. TheMr46,000–48,000 gM moiety is processed to anMr50,000–55,000 glycoprotein, which is resistant to treatment with endoglycosidase H, indicating that processing occurs in the Golgi network. EHV-1 gM forms a dimer in infected cells and the virion, as was demonstrated by the presence of anMr105,000–110,000 gM-containing band in electrophoretically separated lysates of infected cells and purified extracellular virions. TheMr105,000–110,000 protein band containing gM was also observed in lysates of cells that had been transfected with EHV-1 gM DNA. The translation of EHV-1 gM is initiated at the firstin-framemethionine of the gM open reading frame as shown by transient transfection experiments of full-length gM and a truncated gM lacking the aminoterminal 83 amino acids. Functional expression of EHV-1 gM inXenopus laevisoocytes together with voltage-clamp analyses demonstrated that gM per se does not exhibit ion channel activity as had been speculated from the predicted structure of the polypeptide.