This result also implies that the S1 pocket of NS2B/NS3pro is rather specific for charged residues, such as R or K. Comparison of the pair interaction at the other substrate subsites with the NS2B/NS3pro protein pocket concluded that the preference of the interaction between the P2 subsite with the S2 pocket is R > K > Q; between the P3 subsite with the S3 pocket is R/Q/T > K/G