Enzymatic activity of the SARS coronavirus main proteinase dimer

The enzymatic activity of the SARS coronavirus main proteinase dimer was characterized by a sensitive, quantitative assay. The new, fluorogenic substrate, (Ala-Arg-Leu-Gln-NH)2-Rhodamine, contained a severe acute respiratory syndrome coronavirus (SARS CoV) main proteinase consensus cleavage sequence and Rhodamine 110, one of the most detectable compounds known, as the reporter group. The gene for the enzyme was cloned in the absence of purification tags, expressed in Escherichia coli and the enzyme purified. Enzyme activity from the SARS CoV main proteinase dimer could readily be detected at low pM concentrations. The enzyme exhibited a high Km, and is unusually sensitive to ionic strength and reducing agents.