Acting on peptide bonds (peptidases);
Hydrolysis of four peptide bonds in the viral precursor polyprotein, commonly with Asp or Glu in the P6 position, Cys or Thr in P1 and Ser or Ala in P1'
Encoded by the genome of the viruses of the hepatitis C group, and contributes to the maturation of the precursor polyproteins. The enzyme is greatly activated by binding of the 54-residue NS4A 'cofactor' protein also derived from the viral polyprotein. Type example of peptidase family S29. The crystallographic structure shows a chymotrypsin-like fold.