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Pleckstrin Homology-Glucosyltransferases, Rab-like GTPase activators and Myotubularins (PH-GRAM) domain 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. 6 of the 13 MTMRs (MTMRs 5, 9-13) contain naturally occurring substitutions of residues required for catalysis by PTP family enzymes. Although these proteins are predicted to be enzymatically inactive, they are thought to function as antagonists of endogenous phosphatase activity or interaction modules. Most 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, PDZ, and PH domains C-terminal to the coiled-coil region. 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.
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