The hemagglutinin/esterase glycoprotein of bovine coronaviruses: sequence and functional comparisons between virulent and avirulent strains.

The entire nucleotide sequences of the hemagglutinin/esterase (HE) genes specified by the highly virulent strain LY138 and the avirulent strain L9 of bovine coronavirus (BCV) were determined. These sequences were compared with recently published sequences of the HE genes of the Quebec and Mebus strains. A large open reading frame of 1272 nt encoding a protein of 424 amino acid residues was predicted. The putative esterase active site was conserved in the virulent and avirulent BCV strains, indicating that this domain is probably not a determinant for BCV virulence. Four amino acid substitutions occurred between the HE proteins of BCV-L9 and BCV-LY138 (leu to Pro at 5, Leu to Val at 103, Ser to Pro at 367, and Thr to Asn at 379). Monoclonal antibodies specific for the HE glycoprotein inhibited the hemagglutination and acetylesterase activities of BCV-L9, but showed no inhibitory effect on the acetylesterase activity of BCV-LY138. These results suggest that at least one epitope is located proximal to one of the three strain-specific amino acids. Four S-specific monoclonal antibodies inhibited hemagglutination but not acetylesterase activity of BCV-L9, implying that the S glycoprotein can promote hemagglutination of chicken erythrocytes in addition to the HE glycoprotein.