Structural proteins of bovine coronavirus and their intracellular processing.

Deregt, D; Sabara, M; Babiuk, L A

The Quebec isolate of bovine coronavirus (BCV) was found to contain four unique major structural proteins. These proteins consisted of the peplomeric protein (gp190/E2, gp100/E2), the nucleocapsid protein (p53/N) and its apparent trimer (p160/N), a family of small matrix glycoproteins (gp26/E1, gp25/E1 and p23/E1) and the putative haemagglutinin (gp124/E3). Pulse-chase experiments utilizing polyclonal antiserum and monoclonal antibodies indicated that the unique BCV E3 protein had its primary precursor an N-linked glycoprotein with an Mr of 59,000 (gp59) which underwent rapid dimerization by disulphide bond formation to yield gp118. Further glycosylation of gp118 produced gp124/E3 which incorporated fucose. Thus gp124/E3 was probably a homodimer. The processing of the E2 and E1 proteins of BCV was similar to that shown previously for mouse hepatitis virus. A large N-linked precursor glycoprotein, gp170, underwent further glycosylation to yield gp190/E2 before subsequent proteolytic cleavage to yield gp100/E2. The glycosylated E1 (gp26, gp25) proteins arose as a result of O-linked glycosylation of p23/E1 as indicated by the resistance of these species to tunicamycin.