Catalytic Domain Structures of MT-SP1/Matriptase, a Matrix-degrading Transmembrane Serine Proteinase (original) (raw)

2001, Journal of Biological Chemistry

The type II transmembrane multidomain serine proteinase MT-SP1/matriptase is highly expressed in many human cancer-derived cell lines and has been implicated in extracellular matrix re-modeling, tumor growth, and metastasis. We have expressed the catalytic domain of MT-SP1 and solved the crystal structures of complexes with benzamidine at 1.3 Å and bovine pancreatic trypsin inhibitor at 2.9 Å. MT-SP1 exhibits a trypsinlike serine proteinase fold, featuring a unique nine-residue 60-insertion loop that influences interactions with protein substrates. The structure discloses a trypsinlike S1 pocket, a small hydrophobic S2 subsite, and an open negatively charged S4 cavity that favors the binding of basic P3/P4 residues. A complementary charge pattern on the surface opposite the active site cleft suggests a distinct docking of the preceding low density lipoprotein receptor class A domain. The benzamidine crystals possess a freely accessible active site and are hence well suited for soaking small molecules, facilitating the improvement of inhibitors. The crystal structure of the MT-SP1 complex with bovine pancreatic trypsin inhibitor serves as a model for hepatocyte growth factor activator inhibitor 1, the physiological inhibitor of MT-SP1, and suggests determinants for the substrate specificity. The activity of proteolytic enzymes is required at multiple stages during the growth, invasion, and progression of human tumors (for a review, see Ref. 1). For example, these complex processes entail extensive re-modeling of the extracellular matrix as well as the activation of latent growth factors and pro-angiogenic proteins. Consequently, the high level expression of particular proteinases often correlates with poor patient survival for several different cancers (see, for instance, Ref. 2). Among these cancer-associated enzymes are serine proteinases such as urokinase-type plasminogen activator (uPA), 1 elastase,