Purification and partial characterization of poliovirus protease 2A by means of a functional assay

The purification of poliovirus protease 2A from infected cells by a functional assay is described. A small synthetic peptide was cleaved specifically by an esterase present in poliovirus-infected cells. Since the enzyme proved extremely unstable in crude extracts a rapid and efficient purification procedure had to be developed. By treatment with different detergents followed by high-speed centrifugation, the esterase activity was separated from inactivating cellular enzymes and was solubilized. Purification to more than 90% homogeneity could be achieved by a single chromatography step, namely, by gel filtration through Superose 12 under fast-protein liquid chromatography conditions. The esterase activity was associated with a protein of 17,000 daltons and copurified with poliovirus protein 2A. Furthermore, antibodies to 2A specifically precipitated the esterase activity. Thus, the esterase was identified as poliovirus protease 2A. Inhibition studies with known protease inhibitors revealed that 2A is probably a sulfhydryl protease. Of the metal ions tested, only zinc exerted significant inhibitory effects. The esterase activity was optimal near neutral pH and had an extremely short half-life at physiological temperatures.