title: Interaction of recombinant human cystatin C with the cysteine proteinases papain and actinidin.
abstract: The interaction between recombinant human cystatin C and the cysteine proteinases papain and actinidin was studied by spectroscopic, kinetic and equilibrium methods. The absorption, near-u.v.c.d. and fluorescence-emission difference spectra for the cystatin C-proteinase interactions were all found to be similar to the corresponding spectra for chicken cystatin. The kinetics of binding of cystatin C to the two enzymes were best described by a simple reversible one-step bimolecular mechanism, like the kinetics of the reaction of chicken cystatin with several cysteine proteinases. Moreover, the second-order association rate constants at 25 degrees C, pH 7.4 and I0.15, of 1.1 x 10(7) and 2.4 x 10(6) M-1.s-1 for the reactions of cystatin C with papain and actinidin respectively, were similar to the corresponding rate constants for the chicken inhibitor and close to the value expected for a diffusion-controlled rate. The dissociation equilibrium constants, approx. 11 fM and approx. 19 nM for the binding of cystatin C to papain and actinidin respectively, were also comparable with the dissociation constants for chicken cystatin. The affinity between cystatin C and several inactivated papains or actinidins decreased with increasing size of the inactivating group in a manner similar to that in earlier studies with the chicken inhibitor. Together, these results strongly indicate that the mechanisms of the reactions of cystatin C and chicken cystatin with cysteine proteinases are identical or highly similar, but differ from that of reactions between serine-proteinase inhibitors and their target enzymes. The model for the proteinase-inhibitor interaction, based on the X-ray structure of chicken cystatin, therefore should be largely applicable also to human cystatin C.
authors.affiliation: Department of Veterinary Medical Chemistry, Swedish University of Agricultural Sciences, Uppsala Biomedical Center.
authors.forename: P
authors.initials: P
authors.lastname: Lindahl
authors.forename: M
authors.initials: M
authors.lastname: Abrahamson
authors.forename: I
authors.initials: I
authors.lastname: Björk
mesh_terms: D000818:Animals; D002556:Cerebrospinal Fluid Proteins / Q000378:metabolism; D002645:Chickens; D002942:Circular Dichroism; D055316:Cystatin C; D015891:Cystatins / Q000378:metabolism*; D003546:Cysteine Endopeptidases / Q000378:metabolism*; D006801:Humans; D007700:Kinetics; D010206:Papain / Q000378:metabolism*; D011485:Protein Binding; D011487:Protein Conformation; D011994:Recombinant Proteins / Q000378:metabolism; D013056:Spectrophotometry, Ultraviolet
chemical_list: C525030:CST3 protein, human; D002556:Cerebrospinal Fluid Proteins; D055316:Cystatin C; D015891:Cystatins; D011994:Recombinant Proteins; D003546:Cysteine Endopeptidases; C018745:actinidain; D010206:Papain