... termed the ‘occluding loop , occupies the part of the active site cleft on the primed side andblocks access to the active site cleft beyond the S2¢substrate binding site [11,12]. The occluding loop ... form of cathepsin B clearly exposed the relevance of the occluding loop for the exopeptidase activity [11], theydo not explain the mechanisms of endopeptidase activ-ity, nor the inhibition of the ... competewith the occluding loop for binding to the active site, the farther away the occluding loop residues areshifted. As seen in the tetragonal form of the cathepsinB chagasin complex (3CBK), the...