Poliovirus, a picornavirus family member, requires the processing of its poly-protein by its own cysteine proteinase for replication. Oryzacystatin-I and oryzacystatin-II, proteinaceous cysteine proteinase inhibitors (cystatins) of rice seed origin, were found to inhibit the replication of poliovirus effectively in infected Vero cells in vitro. Truncated oryzacystatin-I, which lacks the NH2-terminal 25 amino acid residues of the intact protein, is an even more effective inhibitor, eliciting its effect at concentrations of less than 0.23 nmol/ml. The low molecular weight cysteine proteinase inhibitors, E-64, E-64C and loxistatin, showed no anti-viral effect at any concentration investigated.
