Polypeptide 2A of human rhinovirus type 2: identification as a protease and characterization by mutational analysis

Evidence is presented that the protein 2A of human rhinovirus serotype 2 (HRV2) is a protease. On expression of the VP1-2A region of HRV2 in bacteria, protein 2A was capable of acting on its own N-terminus; derived extracts specifically cleaved a 16 amino acid oligopeptide corresponding to the sequence at the cleavage site. Cleavage of the oligopeptide substrate provides a convenient in vitro assay system. Deletion experiments showed that removal of 10 amino acids from the carboxy terminus inactivated the enzyme. Site-directed mutagenesis identified an essential arginine close to the C-terminus and showed that the enzyme was sensitive to changes in the putative active site. This analysis supports the hypothesis that 2A belongs to the group of sulfhydryl proteases, although sequence comparisons indicate that the putative active site of HRV2 2A is closely related to that of the serine proteases.