Interaction of cystatin C variants with papain and human cathepsins B, H and L

Recombinant human cystatin C and two of its mutants were expressed in Esche richia coli. The recombinant inhibitor was found to be identical to authent ic cystatin C as judged by isoelectric focusing (pI 9.2) and kinetics of in hibition of papain and human cathepsins B, H and L. N-terminal truncation o f 8 residues resulted in a decrease of isoelectric point (pI 7.8), but the inhibitory properties were similar to those of recombinant cystatin C, sugg esting that Leu9 is a critical residue for the inhibition. The mutation of Trp106 to Ser, however, resulted in a decreased affinity of the inhibitor f or the enzymes tested, with the largest effect on cathepsin B inhibition (s imilar to 100-fold increase in K-i).