Myotubularian 1 protein (MTM1) Pleckstrin Homology-Glucosyltransferases, Rab-like GTPase activators and Myotubularins (PH-GRAM) domain
MTM1 is a member of the myotubularin protein phosphatase gene family. It is required for muscle cell differentiation and mutations in this gene have been identified as being responsible for X-linked myotubular myopathy, a severe congenital muscle disorder characterized by defective muscle cell development. Since its initial discovery, there have been an additional 14 myotubularin-related proteins identified. MTM1 binds to phosphoinositide lipids through its PH-GRAM domain, and can hydrolyze phosphatidylinositol(3)-phosphate and phosphatidylinositol(3,5)-biphosphate in vitro. The protein can self-associate and form heteromers with MTMR12. MTM1 contains a N-terminal PH-GRAM domain, a Rac-induced recruitment domain (RID) domain, an active PTP domain, a SET-interaction domain, and a C-terminal coiled-coil region. Myotubularin-related proteins are a subfamily of protein tyrosine phosphatases (PTPs) that dephosphorylate D3-phosphorylated inositol lipids. Mutations in this family cause the human neuromuscular disorders myotubular myopathy and type 4B Charcot-Marie-Tooth syndrome. The GRAM domain, found in myotubularins, glucosyltransferases, and other putative membrane-associated proteins, is part of a larger motif with a pleckstrin homology (PH) domain fold. All MTMRs contain a N-terminal PH-GRAM domain, a Rac-induced recruitment domain (RID) domain, a PTP domain (which may be active or inactive), a SET-interaction domain, and a C-terminal coiled-coil region. In addition some members contain DENN domain N-terminal to the PH-GRAM domain and FYVE and PH domains C-terminal to the coiled-coil region.
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