Regulation of myotubularin-related (MTMR)2 phosphatidylinositol phosphatase by MTMR5, a catalytically inactive phosphatase.

The myotubularin (MTM) family constitutes one of the most highly conserved protein-tyrosine phosphatase subfamilies in eukaryotes. MTM1, the archetypal member of this family, is mutated in X-linked myotubular myopathy, whereas mutations in the MTM-related (MTMR)2 gene cause the type 4B1 Charcot-Marie-Tooth disease, a severe hereditary motor and sensory neuropathy. In this study, we identified a protein that specifically interacts with MTMR2 but not MTM1. The interacting protein was shown by mass spectrometry to be MTMR5, a catalytically inactive member of the MTM family. We also demonstrate that MTMR2 interacts with MTMR5 via its coiled-coil domain and that mutations in the coiled-coil domain of either MTMR2 or MTMR5 abrogate this interaction. Through this interaction, MTMR5 increases the enzymatic activity of MTMR2 and dictates its subcellular localization. This article demonstrates an active MTM member being regulated by an inactive family member.