Structure and Expression of the Bovine Coronavirus Hemagglutinin Protein
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cDNA clones prepared from genomic RNA of the Mebus strain of bovine Coronavirus (BCV) were sequenced to reveal the hemagglutinin (H) gene of 1,272 bases that predicts a 47,700 mol. wt. apoprotein of 424 amino acids. The H gene mapped on the immediate 5′ side of the peplomer gene. The H protein sequence revealed a putative N-terminal signal peptide of 18 amino acids, 9 potential glycosylation sites, 14 cysteine residues, and a potential C-terminal anchor region of 26 amino acids. When transcripts of the gene were translated in vitro in the presence of microsomes, signal cleavage, glycosylation, and membrane anchorage were observed, but not disulfide-linked dimerization. Translation of a truncated mRNA having no sequence for the C-terminal anchor resulted in a nonanchored, intraluminal (intramicrosomal) protein. When the H protein was expressed in cells in the absence of other coronaviral proteins, it became glycosylated, dimerized, and transported to the cell surface. The BCV hemagglutinin protein, therefore, is a type 1 glycoprotein that contains all the information it needs for signal cleavage, glycosylation, disulfide-linked dimerization, and transport to the cell surface.
KeywordsSignal Cleavage Hemagglutinin Protein Bovine Coronavirus Lipofectin Reagent Acetyl Esterase Activity
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