Picornain 3C, a protease present in picornaviruses, exhibits endopeptidase activity by specifically cleaving Gln-Gly bonds within the poliovirus polyprotein and, through substitution, cleaves Glu for Gln, and Ser or Thr for Gly in other picornaviruses. This protease operates on non-terminal sequences and intermediates between serine peptidase chymotrypsin and cysteine peptidase papain, showcasing its role in viral polyprotein processing [1].