Proteolytic enhancement of rotavirus infectivity: molecular mechanisms

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Abstract
The polypeptide compositions of single-shelled and double-shelled simian rotavirus particles were modified by exposure to proteolytic enzymes. Specificially, a major outer capsid polypeptide (VP3) having a MW of 88,000 in double-shelled particles was cleaved by trypsin to yield 2 polypeptides, VP5* and VP8* (MW, 60,000 and 28,000, respectively). The cleavage of VP3 by enzymes that enhanced infectivity (trypsin, elastase and pancreatin) yielded different products compared to those detected when VP3 was cleaved by chymotrypsin, which did not enhance infectivity. The appearance of VP5* was correlated with an enhancement of infectivity. Cleavages of the major internal capsid polypeptide VP2 were also observed. The VP2 cleavage products had MW similar to those of known structural and nonstructural rotavirus polypeptides. The precursor-product relationships were confirmed by comparing the peptide maps of the polypeptides generated by digestions with V-8 protease and chymotrypsin. The remaining rotavirus structural polypeptides, including the outer capsid glycoproteins (VP7 and 7a), were not altered by exposure to pancreatic enzymes. Cleavage of VP3 was not required for virus assembly and specific cleavage of the polypeptides occurred only on assembled particles. The role of cleavage activation in other virus-specific biological functions (e.g., hemagglutination and virulence) is also discussed.