Enzymatic Characterization of Refolded Human Rhinovirus Type 14 2A Protease Expressed in Escherichia coli

Reported here is the production of recombinant human rhinovirus 14 (HRV14) 2A protease from bacterial cells transformed with a heat-inducible plasmid containing the HRV14 2A cDNA sequence. Overexpressed 2A protein partitioned into the inclusion bodies was solubilized in urea and then refolded in the presence of Zn(2+). Transition metals were required for the restoration of 2A protease activity as a structural component, but appeared to be inhibitory if added exogenously once the enzyme was refolded. Based on the cleavage specificity studies, a colorimetric assay was developed for the highly purified HRV14 2A protease. A peptide with the sequence RKGDIKSY–p-nitroanilide was found to be cleaved by the 2A protease with a k(cat)/K(m) ratio of ∼335 M(−1)s(−1), which allows its activity to be measured continuously with a spectrophotometer or a microplate reader.