The sequence of the spike (also called peplomer or E2) protein gene of the Mebus strain of bovine coronavirus (BCV) was obtained from cDNA clones of genomic RNA. The gene sequence predicts a 150,825 mol wt apoprotein of 1363 amino acids having an N-terminal hydrophobic signal sequence of 17 amino acids, 19 potential N-linked glycosylation sites, a hydrophobic anchor sequence of approximately 17 amino acids near the C terminus, and a hydrophilic cysteine-rich C terminus of 35 amino acids. An internal Lys-Arg-Arg-Ser-Arg-Arg sequence predicts a protease cleavage site between amino acids 768 and 769 that would separate the S apoprotein into S1 and S2 segments of 85690 and 65153 mol wt, respectively. Amino terminal amino acid sequencing of the virion-derived gp 100 spike subunit confirmed the location of the predicted cleavage site, and established that gp 120 and gp 100 are the glycosylated virion forms of the S1 and S2 subunits, respectively. Sequence comparisons between BCV and the antigenically related mouse hepatitis coronavirus revealed more sequence divergence in the putative knob region of the spike protein (S1) than in the stem region (S2).

The sequence of the hemagglutinin-esterase (HE) gene for the Mebus strain of bovine coronavirus was obtained from cDNA clones, and its deduced product is a 47,700-kilodalton apoprotein of 424 amino acids. Expression of the HE protein in vitro in the presence of microsomes revealed N-terminal signal peptide cleavage and C-terminal anchorage but not disulfide-linked dimerization. Dimerization was observed only after expression in vivo, during which HE was also transported to the cell surface.

Early reviews on coronavirus structure (SiddeH et a1., 1983a,bj Sturman and Holmes, 1985) described coronaviruses as having three major structural proteins: a large-surface (or peplomer) glycoprotein of around 200 kDa, a phosphorylated nucleocapsid pro tein of around 50 kDa, and a glycosylated, multispanning membrane protein of around 30 kDa. This description was based primarily on studies of the prototypic avian infectious bronchitis virus (IBV) and the highly studied mouse hepatitis virus (MHV), strain A59. Although IBV was shown early on to have a weak hemagglutinating property, detection of the hemagglutinating activity required that the virus first be treated with phospholipase C or concentrated by centrifugation in sucrose gradients (Bingham et a1., 1975). Not all strains of IBV demonstrated hemagglutination, however, and hemagglutinating activity by IBV, as weH as by the porcine transmissible gastroenteritis virus (TGEV) (Noda et a1., 1987, 1988) was probably a cryptic property

No abstract

SUMMARYThe haemagglutinin molecule on the bovine enteric coronavirus has been identified as a glycoprotein of 140K composed of disulphide-linked subunits of 65K. In this study, we have shown the subunits to be identical by demonstrating an unambiguous aminoterminal amino acid sequence. The unglycosylated subunit was found to have an M r of 42.5K and to undergo rapid disulphide linkage and glycosylation. Glycosylation was found to be of the asparagine-linked type and some of the oligosaccharides underwent processing to complex forms. Studies with inhibitors of glycosylation suggested that a processing of the haemagglutinin oligosaccharide takes place on the virion whilst it is in the Golgi apparatus. Each haemagglutinin subunit on the mature virion was estimated to possess six or seven carbohydrate chains of either the high-mannose or hybrid type, and three or four chains of the complex type.