The three-dimensional structure of the complex of proteinase K with its naturally occurring protein inhibitor, PKI3

Proteinase K forms a 1:1 stable complex with its naturally occurring protein inhibitor, PKI3. The crystal structure of this complex has been determined by a combination of molecular replacement and single isomorphous replacement methods. The model comprises all of the 459 residues: 279 for proteinase K and 180 for PKI3, and it was refined to an R-factor of 19.2% at a resolution of 2.5 A. Association of these two molecules in the complex indicates the binding of PKI3 in the substrate recognition site of the enzyme. The active serine residue of proteinase K in this complex possesses a somewhat different configuration to that found in its native structure and hence renders the enzyme inactive.