The catalytic domain of activated collagenase I (MMP-1) is absolutely required for interaction with its specific inhibitor, tissue inhibitor of metalloproteinases-1 (TIMP-1)

Here, we describe the production of recombinant human tissue inhibitor of metalloproteinases-l (rTIMP-1) and wild-type and mutant human collagenase type I (rMMP-1) proteins in SF9 cells by the baculovirus expression system. Wild-type MMP-1, as well as the MMP-1 mutant lacking the C-terminal hemopexin-like domain [des-(248-450)-MMP-1], exhibit enzymatic activity upon cleavage of the pro-domain by treatment with trypsin or 4-aminophenylmercuric acetate. Enzyme activity of both proteins can be inhibited by addition of rTIMP. Deletion of the complete active-site [des-(161-228)-MMP-1] within the catalytic domain, or mutation of a single His residue of the Zn2+ binding domain (His199), generates stable forms of MMP-1 proteins which are unable to digest collagen type I or beta-casein. In addition to co-immunoprecipitation analysis, we have established a rapid and sensitive ELISA assay using immobilized rTIMP to determine the structural requirements of MMP-1 to form complexes with its inhibitor. Only the activated and not the latent forms of wild-type and C-terminal mutant des-(248-450)MMP-1 proteins are able to form complexes with TIMP. Neither mutation of His199, nor deletion mutants des-(161-228)-MMP-1 and des-(161-228/248-450)-MMP-1, interact with TIMP. This demonstrates that the C-terminal hemopexin domain of MMP-1, in contrast to the corresponding regions of gelatinase A and gelatinase B, does not interact with TIMP-1. In summary, we have shown that the integrity of the catalytic domain of MMP-1 and its ability to bind Zn2+ is absolutely required for complex formation with TIMP-1, which further underlines the importance of this region for proper regulation of enzymatic activity of MMP-1.