Polymorphism of human cytomegalovirus glycoproteins characterized by monoclonal antibodies

Monoclonal antibody panels selected in this and preceding studies were employed to begin to characterize the properties of human cytomegalovirus (CMV) glycoproteins. The results were as follows. (i) Four antigenically distinct CMV glycoproteins designated as gA, gB, gC, and gD have been identified. (ii) gA, gC, and gD each form several bands when immune precipitated from infected cell extracts by the corresponding monoclonal antibodies and electrophoretically separated in sodium dodecyl sulfate-polyacrylamide gels. In contrast, gB migrated at one broad band with an apparent molecular weight in the range of 116,000 to 123,000. Bands with different molecular weights were shown to share antigenic determinants by reactivity of monoclonal antibodies with electrophoretically separated polypeptides immobilized on nitrocellulose. (iii) A panel of 16 monoclonal antibodies to gA precipitated a family of glycoproteins 160,000-148,000, 142,000, 138,000, 123,000-107,000, 95,000, and 58,500 in apparent molecular weight designated as gA1 through gA6, respectively. (iv) To identify partially glycosylated precursors of gA, infected cells were treated with tunicamycin or deoxyglucose and reacted with different monoclonal antibodies. Tunicamycin-treated infected cells labeled for a short pulse or longer intervals contained only gA5. Whereas cells treated with deoxyglucose during a pulse contained gA4, those labeled for a longer interval contained gA6 and an additional band approximately 56,500 in apparent molecular weight designated gA7. (v) Precipitates of gA from infected cells labeled for a short pulse contained gA2 and gA3 which appear to be products of rapid glycosylation. After a chase, trace amounts of gA1 and gA6 were also precipitated suggesting that these are products of slow post-translational processing. (vi) Endo-beta-N-acetylglucosaminidase H was used to identify the forms of gA which contain high-mannose oligosaccharide chains. After treatment, the electrophoretic mobility of gA2, gA3, and gA6 increased significantly suggesting that these forms contain high-mannose chains cleaved by the enzyme. A hypothesis for processing gA is presented.