Structural analysis of virion proteins of the avian coronavirus infectious bronchitis virus

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Abstract
Six major polypeptides were found in virions of the avian coronavirus infectious bronchitis virus grown in chicken embryo kidney tissue culture: 4 glycoproteins, GP84, GP36, GP31 and GP28 and 2 non-glycosylated proteins, P51 and P23. Three minor species: 2 glycoproteins, GP90 and GP59, and 1 non-glycosylated protein, P14 were also detected. Two-dimensional tryptic peptide mapping showed that GP36, GP31, GP28 and P23 comprise a group of closely related proteins which were designated as the P23 family, but the other proteins are distinct. Analysis by partial proteolytic digestion of the P23 family, labeled biosynthetically with [35S]methionine, and P23, labeled with [35S]formyl-methionine by in vitro translation of RNA from infected cells, revealed that the proteins of the P23 family differ in their amino-terminal domains. Similar analysis of GP31 and GP36 labeled with [3H]mannose showed that the partial proteolytic fragments unique to these proteins were glycosylated. Differences in glycosylation in the amino-terminal domains apparently contributes to the marked polymorphism of the P23 family. The results are discussed with respect to possible models for synthesis of the virion proteins.