POSTOLIGOMERIZATION FOLDING OF HUMAN CYTOMEGALOVIRUS GLYCOPROTEIN-B -IDENTIFICATION OF FOLDING INTERMEDIATES AND IMPORTANCE OF DISULFIDE BONDING

Human cytomegalovirus glycoprotein B (gB or UL55) has been demonstrate d to be a disulfide-linked homodimer within the envelope of mature vir ions. Previously, it has been shown that gB undergoes a rapid dimeriza tion nearly coincident with its synthesis. Following dimerization, the molecule slowly folds into a form which can be transported from the e ndoplasmic reticulum. In this study we have examined the prolonged fol ding of gB by using a set of defined gB-reactive murine monoclonal ant ibodies and gB expressed as a recombinant protein in the absence of ot her human cytomegalovirus proteins. Our results have documented a fold ing pathway consistent with the relatively rapid dimerization of the t ranslation product followed by delayed conversion into a fully folded molecule. Assembly of the dominant antigenic domain of gB, AD-1, prece ded dimerization and folding of the molecule. The fully folded dimer w as heat stable, but its conformation was altered by treatment with 2% sodium dodecyl sulfate (SDS), whereas an oligomeric folding intermedia te was both heat and SDS stable. Postoligomerization disulfide bond fo rmation could be demonstrated during folding of gB, suggesting that th e formation of these covalent bonds could contribute to the prolonged folding of this glycoprotein.