Mapping and characterization of the functional epitopes of tissue inhibitor of metalloproteinases (TIMP)-3 using TIMP-1 as the scaffold: a new frontier in TIMP engineering.

Tumor necrosis factor-alpha (TNF-alpha) converting enzyme (TACE/ADAM-17) is responsible for the release of TNF-alpha, a potent proinflammatory cytokine associated with many chronic debilitating diseases such as rheumatoid arthritis. Among the four variants of mammalian tissue inhibitor of metalloproteinases (TIMP-1 to -4), TACE is specifically inhibited by TIMP-3. We set out to delineate the basis for this specificity by examining the solvent accessibility of every epitope on the surface of a model of the truncated N-terminal domain form of TIMP-3 (N-TIMP-3) in a hypothetical complex with the crystal structure of TACE. The epitopes suspected of interacting with TACE were systematically transplanted onto N-TIMP-1. We succeeded in transforming N-TIMP-1 into an active inhibitor for TACE (K(i)(app) 15 nM) with the incorporation of Ser4, Leu67, Arg84, and the TIMP-3 AB-loop. The combined effects of these epitopes are additive. Unexpectedly, introduction of "super-N-TIMP-3" epitopes, defined in our previous work, only impaired the affinity of N-TIMP-1 for TACE. Our mutagenesis results indicate that TIMP-3-TACE interaction is a delicate process that requires highly refined surface topography and flexibility from both parties. Most importantly, our findings confirm that the individual characteristics of TIMP could be transplanted from one variant to another.

The C-terminal domains of TACE weaken the inhibitory action of N-TIMP-3.

Tumor necrosis factor-alpha converting enzyme (TACE) is an ADAM (a disintegrin and metalloproteinases) that comprises an active catalytic domain and several C-terminal domains. We compare the binding affinity and association rate constants of the N-terminal domain form of wild-type tissue inhibitor of metalloproteinase (TIMP-3; N-TIMP-3) and its mutants against full-length recombinant TACE and the truncated form of its catalytic domain. We show that the C-terminal domains of TACE substantially weaken the inhibitory action of N-TIMP-3. Further probing with hydroxamate inhibitors indicates that both forms of TACE have similar active site configurations. Our findings highlight the potential role of the C-terminal domains of ADAM proteinases in influencing TIMP interactions.

Tailoring tissue inhibitor of metalloproteinases-3 to overcome the weakening effects of the cysteine-rich domains of tumour necrosis factor-alpha converting enzyme.

Tumour necrosis factor-alpha (TNF-alpha) converting enzyme (TACE) is a membrane-anchored, multiple-domain zinc metalloproteinase responsible for the release of the potent pro-inflammatory cytokine, TNF-alpha. The extracellular part of the active enzyme is composed of a catalytic domain and several cysteine-rich domains. Previously, we reported that these cysteine-rich domains significantly weakened the inhibitory potency of the N-terminal-domain form of tissue inhibitor of metalloproteinases-3 (N-TIMP-3). In the present paper, we describe a novel strategy developed to overcome this weakening effect. We have engineered a new generation of N-TIMP-3 mutants that are capable of withstanding the repulsion of the cysteine-rich domains by the formation of electrostatic bonds with the catalytic domain of the enzyme. These N-TIMP-3 mutants displayed markedly improved binding affinity with the soluble extracellular domain form of recombinant TACE. With K (i) (app) values of <0.1 nM, these mutants were dramatically better than the wild-type N-TIMP-3 [K (i) (app) 1.7 nM]. We accounted for this by proposing that Glu(31), an acidic residue situated at the base of the AB-loop of N-TIMP-3, is drawn into contact with Lys(315), a prominent basic residue adjacent to the TACE catalytic site. The mutagenesis strategy involved reorientation of the edge of N-TIMP-3; in particular, the beta-strand A where Glu(31) was located. Further expression of one of the mutants, Lys(26/27/30/76)-->Glu, in a mammalian expression system confirmed that TIMP-3 associates with the extracellular matrix via its C-terminal domain.

Engineering N-terminal domain of tissue inhibitor of metalloproteinase (TIMP)-3 to be a better inhibitor against tumour necrosis factor-alpha-converting enzyme.

We previously reported that full-length tissue inhibitor of metalloproteinase-3 (TIMP-3) and its N-terminal domain form (N-TIMP-3) displayed equal binding affinity for tissue necrosis factor-alpha (TNF-alpha)-converting enzyme (TACE). Based on the computer graphic of TACE docked with a TIMP-3 model, we created a number of N-TIMP-3 mutants that showed significant improvement in TACE inhibition. Our strategy was to select those N-TIMP-3 residues that were believed to be in actual contact with the active-site pockets of TACE and mutate them to amino acids of a better-fitting nature. The activities of these mutants were examined by measuring their binding affinities (K(app)(i)) and association rates (k(on)) against TACE. Nearly all mutants at position Thr-2 exhibited slightly impaired affinity as well as association rate constants. On the other hand, some Ser-4 mutants displayed a remarkable increase in their binding tightness with TACE. In fact, the binding affinities of several mutants were less than 60 pM, beyond the sensitivity limits of fluorimetric assays. Further studies on cell-based processing of pro-TNF-alpha demonstrated that wild-type N-TIMP-3 and one of its tight-binding mutants, Ser-4Met, were capable of inhibiting the proteolytic shedding of TNF-alpha. Furthermore, the Ser-4Met mutant was also significantly more active (P<0.05) than the wild-type N-TIMP-3 in its cellular inhibition. Comparison of N-TIMP-3 and full-length TIMP-3 revealed that, despite their identical TACE-interaction kinetics, the latter was nearly 10 times more efficient in the inhibition of TNF-alpha shedding, with concomitant implications for the importance of the TIMP-3 C-terminal domain in vivo.