Tissue inhibitors of metalloproteinases (TIMPs) inhibit matrix metalloproteinases (MMPs) by forming a 1:1 stoichiometric complex, but the inhibition mechanism of these inhibitors is not known. Here we have investigated the reactive site of TIMP-1 by its proteinase susceptibility before and after forming a complex with MMP-3 (stromelysin 1). When TIMP-1 was allowed to react with human neutrophil elastase, its inhibitory activity was destroyed. This resulted from cleavage of the Val69–Cys70 bond. However, cleavage of this bond by neutrophil elastase was prevented when TIMP-1 formed a complex with the catalytic domain of MMP-3, and full TIMP-1 activity was restored after dissociation of the complex at pH 3.0 in the presence of EDTA. These results indicate that the region around Val69 closely associates with an active MMP. The three-dimensional structure of the N-terminal domain of TIMP-2 elucidated by NMR studies [Williamson, Martorell, Carr, Murphy, Docherty, Freedman and Feeney (1994) Biochemistry 33, 11745–11759] reveals that Val69 and Cys70 form part of an extended ridge that also includes the N-terminal section of the inhibitor. This region is probably involved in the interaction with the catalytic domains of MMPs.

This content is only available as a PDF.