Phosphatase Subfamily MTMR5
Phosphatase Classification: FoldCC1: Superfamily CC1: Family Myotubularin: Subfamily MTMR5 (SBF)
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Evolution
MTMR5 subfamily is found throughout metazoan. It consists of two members in human, MTMR5 and MTMR13, also called SBF1 and SBF2, respectively. In fruit fly and C elegans, a single copy is found.
Domain Structure
MTMR5 subfamily has a DENN domain, PH/GRAM domain, phosphatase domain, coiled-coil domain and PH domain. The GRAM domain is similar to PH domain in structure and is found in membrane-associated proteins.
DENN domains interact directly with members of the Rab family of small GTPases and that DENN domains function enzymatically as Rab-specific guanine nucleotide exchange factors. MTMR5 and MTMR13 have GEF activity toward Rab28, a poorly characterized and distant member of the Rab superfamily[1].
Coiled-coil domain mediates the interactions of MTMR5 and MTMR13 with MTMR2, which results in the increase of enzymatic activity of MTMR2 [2, 3].
Catalytic activity and functions
MTMR5 subfamily is conservatively inactive in metazoan.
Human MTMR5 interact with MTMR2 (see MTMR1 subfamily) via its coiled-coil domain and 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 [2]. This is a good example of inactive phosphatase functions as regulator of active phosphatase.
Disease
Mice deficient for MTMR5 exhibit male infertility characterized by azoospermia [4].
Loss of Mtmr13 in mice leads to a peripheral neuropathy with many of the key features of Charcot–Marie–Tooth disease type 4B (CMT4B), which is a severe, demyelinating peripheral neuropathy characterized by slowed nerve conduction velocity, axon loss, and distinctive myelin outfolding and infolding. It worthy pointing out that recessive mutations in either MTMR2 or MTMR13 lead to nearly indistinguishable forms of CMT4B [5].
References
- Yoshimura S, Gerondopoulos A, Linford A, Rigden DJ, and Barr FA. Family-wide characterization of the DENN domain Rab GDP-GTP exchange factors. J Cell Biol. 2010 Oct 18;191(2):367-81. DOI:10.1083/jcb.201008051 |
- Kim SA, Vacratsis PO, Firestein R, Cleary ML, and Dixon JE. Regulation of myotubularin-related (MTMR)2 phosphatidylinositol phosphatase by MTMR5, a catalytically inactive phosphatase. Proc Natl Acad Sci U S A. 2003 Apr 15;100(8):4492-7. DOI:10.1073/pnas.0431052100 |
- Robinson FL and Dixon JE. The phosphoinositide-3-phosphatase MTMR2 associates with MTMR13, a membrane-associated pseudophosphatase also mutated in type 4B Charcot-Marie-Tooth disease. J Biol Chem. 2005 Sep 9;280(36):31699-707. DOI:10.1074/jbc.M505159200 |
- Firestein R, Nagy PL, Daly M, Huie P, Conti M, and Cleary ML. Male infertility, impaired spermatogenesis, and azoospermia in mice deficient for the pseudophosphatase Sbf1. J Clin Invest. 2002 May;109(9):1165-72. DOI:10.1172/JCI12589 |
- Robinson FL, Niesman IR, Beiswenger KK, and Dixon JE. Loss of the inactive myotubularin-related phosphatase Mtmr13 leads to a Charcot-Marie-Tooth 4B2-like peripheral neuropathy in mice. Proc Natl Acad Sci U S A. 2008 Mar 25;105(12):4916-21. DOI:10.1073/pnas.0800742105 |
