Myotubularin-related protein 12 (MTMR12), also known 3-phosphatase adapter protein (3-PAP), belongs to the myotubularin family. It is a catalytically inactive phosphatase that plays a role as an adapter for the phosphatase myotubularin to regulate myotubularin intracellular location [, ]. Knockdown of the mtmr12 gene in zebrafish results in skeletal muscle defects and impaired motor function [].The myotubularin family constitutes a large group of conserved proteins, with 14 members in humans consisting of myotubularin (MTM1) and 13 myotubularin-related proteins (MTMR1-MTMR13). Orthologues have been found throughout the eukaryotic kingdom, but not in bacteria. MTM1 dephosphorylates phosphatidylinositol 3-monophosphate (PI3P) to phosphatidylinositol and phosphatidylinositol 3,5-bisphosphate [PI(3,5)P2]to phosphatidylinositol 5-monophosphate (PI5P) [, ]. The substrate phosphoinositides (PIs) are known to regulate traffic within the endosomal-lysosomal pathway []. MTMR1, MTMR2, MTMR3, MTMR4, and MTMR6 have also been shown to utilise PI(3)P as a substrate, suggesting that this activity is intrinsic to all active family members. On the other hand, six of the MTM family members encode for catalytically inactive phosphatases. Inactive myotubularin phosphatases contain substitutions in the Cys and Arg residues of the Cys-X5-Arg motif. MTM pseudophosphatases have been found to interact with MTM catalytic phosphatases []. The myotubularin family includes several members mutated in neuromuscular diseases or associated with metabolic syndrome, obesity, and cancer [].
