Myotubularian (MTM) related 14 protein (MTMR14) Pleckstrin Homology-Glucosyltransferases, Rab-like GTPase activators and Myotubularins (PH-GRAM) domain
MTMR14 is a member of the myotubularin protein phosphatase gene family. MTMR14 binds to phosphoinositide lipids through its PH-GRAM domain, and can hydrolyze phosphatidylinositol(3)-phosphate and phosphatidylinositol(3,5)-biphosphate in vitro. MTMR14 plays a role in the regulation of autophagy and mutations in MTMR14 result in autosomal dominant centronuclear myopathy. MTMR14 contain a N-terminal PH-GRAM domain, a Rac-induced recruitment domain (RID) domain, an active PTP domain, a SET-interaction domain (SID), a coiled-coil region, and a C-terminal PDZ 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 (SID), 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. The PH domain family possesses multiple functions including the ability to bind phosphoinositides via its beta1/beta2, beta3/beta4, and beta6/beta7 connecting loops and to other proteins. However, no phosphoinositide binding sites have been found for the MTMRs to date.
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