Structure-function relationships in the tissue inhibitors of metalloproteinases.

The tissue inhibitors of metalloproteinases (TIMPs) are proteins that specifically inhibit the matrix metalloproteinases. They consist of two distinct structural and functional domains. In order to elucidate the role of these domains, we have prepared mutants of TIMP-1 and TIMP-2 that lack a C-terminal domain. The N-terminal domain alone is an efficient inhibitor of all the matrix metalloproteinases through interaction with the enzyme catalytic domain. The C-terminal domain has at least two separate enzyme binding sites, one for gelatinase A and the other for stromelysin-1. The rate of inhibition of either enzyme is increased by interaction with the TIMP C-terminal domain. As no conformational change is observed, we propose that the rate enhancement is due to an anchoring effect in which binding of the TIMP C-terminal domain aligns the TIMP N-terminal domain with the enzyme active site. Site-directed mutagenesis of TIMP-1 has demonstrated that the N-terminal amino acids, His7 and Gln9, are important for inhibition.