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protein tyrosine phosphatase-like pseudophosphatase domain of myotubularin related phosphoinositide phosphatase 13 Myotubularin related phosphoinositide phosphatase 13 (MTMR13), also known as SET binding factor 2 (SBF2), is enzymatically inactive and contains a variety of other domains, including a DENN and a PH-like domain. Mutations in MTMR13 causes Charcot-Marie-Tooth type 4B2, a severe childhood-onset neuromuscular disorder, characterized by demyelination and redundant loops of myelin known as myelin outfoldings, a similar phenotype as mutations in MTMR2. In general, myotubularins are a unique subgroup of protein tyrosine phosphatases that use inositol phospholipids, rather than phosphoproteins, as substrates. MTMR13 is a pseudophosphatase that lacks the catalytic cysteine in its catalytic pocket. It is believed to interact with MTMR2 and stimulate its phosphatase activity. It is also a guanine nucleotide exchange factor (GEF) which may activate RAB28, promoting the exchange of GDP to GTP and converting inactive GDP-bound Rab proteins into their active GTP-bound form.
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