Crystal structure of the stromelysin-3 (MMP-11) catalytic domain complexed with a phosphinic inhibitor mimicking the transition-state.

Stromelysin-3 (ST3) is a matrix metalloproteinase (MMP-11) whose proteolytic activity plays an important role in tumorigenicity enhancement. In breast cancer, ST3 is a bad prognosis marker: its expression is associated with a poor clinical outcome. This enzyme therefore represents an attractive therapeutic target. The topology of matrix metalloproteinases (MMPs) is remarkably well conserved, making the design of highly specific inhibitors difficult. The major difference between MMPs lies in the S(1)' subsite, a well-defined hydrophobic pocket of variable depth. The present crystal structure, the first 3D-structure of the ST3 catalytic domain in interaction with a phosphinic inhibitor mimicking a (d, l) peptide, clearly demonstrates that its S(1)' pocket corresponds to a tunnel running through the enzyme. This open channel is filled by the inhibitor P(1)' group which adopts a constrained conformation to fit this pocket, together with two water molecules interacting with the ST3-specific residue Gln215. These observations provide clues for the design of more specific inhibitors and show how ST3 can accommodate a phosphinic inhibitor mimicking a (d, l) peptide. The presence of a water molecule interacting with one oxygen atom of the inhibitor phosphinyl group and the proline residue of the Met-turn suggests how the intermediate formed during proteolysis may be stabilized. Furthermore, the hydrogen bond distance observed between the methyl of the phosphinic group and the carbonyl group of Ala182 mimics the interaction between this carbonyl group and the amide group of the cleaved peptidic bond. Our crystal structure provides a good model to study the MMPs mechanism of proteolysis.

Sequence analysis of the CAG triplet repeats region in the Huntington disease gene (IT15) in several mammalian species.

Huntington's disease (HD) is a progressive neurodegenerative disease linked to abnormally expanded CAG repeats in the first exon of the IT15 gene. Neither HD or other glutamine expansion triplet disease has not yet been described in other species as human. In this study, we sequenced the region containing the CAG repeat expansion region of the corresponding IT15 gene in several mammalian species. In all investigated species, the number of CAG found is equal or inferior to the normal range of human IT15 alleles. The longer uninterrupted CAG stretch was found in the pig and consists of 18 CAG. In the other species, the CAG stretch was shorter and/or interrupted by other triplets. The proline encoding region following the CAG stretch is conserved in the mammalian species studied here and the number of proline is few or not reduced compared to the number of the glutamine codon repeats region.