title: Specificity of the myotubularin family of phosphatidylinositol-3-phosphatase is determined by the PH/GRAM domain.
abstract: Myotubularins (MTM) are a large subfamily of lipid phosphatases that specifically dephosphorylate at the D3 position of phosphatidylinositol 3-phosphate (PI(3)P) in PI(3)P and PI(3,5)P2. We recently found that MTMR6 specifically inhibits the Ca2+-activated K+ channel, KCa3.1, by dephosphorylating PI(3)P. We now show that inhibition is specific for MTMR6 and other MTMs do not inhibit KCa3.1. By replacing either or both of the coiled-coil (CC) and pleckstrin homology/GRAM (PH/G) domains of MTMs that failed to inhibit KCa3.1 with the CC and PH/G domains of MTMR6, we found that chimeric MTMs containing both the MTMR6 CC and PH/G domains functioned like MTMR6 to inhibit KCa3.1 channel activity, whereas chimeric MTMs containing either domain alone did not. Immunofluorescent microscopy demonstrated that both the MTMR6 CC and PH/G domains are required to co-localize MTMR6 to the plasma membrane with KCa3.1. These findings support a model in which two specific low affinity interactions are required to co-localize MTMR6 with KCa3.1: 1) between the CC domains on MTMR6 and KCa3.1 and (2) between the PH/G domain and a component of the plasma membrane. Our inability to detect significant interaction of the MTMR6 G/PH domain with phosphoinositides suggests that this domain may bind a protein. Identifying the specific binding partners of the CC and PH/G domains on other MTMs will provide important clues to the specific functions regulated by other MTMs as well as the mechanism(s) whereby loss of some MTMs lead to disease.
authors.affiliation: Department of Medicine, The Skirball Institute, New York University School of Medicine, New York, NY 10016, USA.
authors.forename: Papiya
authors.initials: P
authors.lastname: Choudhury
authors.forename: Shekhar
authors.initials: S
authors.lastname: Srivastava
authors.forename: Zhai
authors.initials: Z
authors.lastname: Li
authors.forename: Kyung
authors.initials: K
authors.lastname: Ko
authors.forename: Mamdouh
authors.initials: M
authors.lastname: Albaqumi
authors.forename: Kartik
authors.initials: K
authors.lastname: Narayan
authors.forename: William A
authors.initials: WA
authors.lastname: Coetzee
authors.forename: Mark A
authors.initials: MA
authors.lastname: Lemmon
authors.forename: Edward Y
authors.initials: EY
authors.lastname: Skolnik
mesh_terms: D000818:Animals; D016466:CHO Cells; D002462:Cell Membrane / Q000378:metabolism; D006224:Cricetinae; D004285:Dogs; D015971:Gene Expression Regulation, Enzymologic; D051660:Intermediate-Conductance Calcium-Activated Potassium Channels / Q000737:chemistry; D018408:Patch-Clamp Techniques; D010716:Phosphatidylinositols / Q000737:chemistry; D010744:Phosphoric Monoester Hydrolases / Q000737:chemistry; D010766:Phosphorylation; D017434:Protein Structure, Tertiary; D017027:Protein Tyrosine Phosphatases / Q000737:chemistry* / Q000378:metabolism; D054558:Protein Tyrosine Phosphatases, Non-Receptor; D011993:Recombinant Fusion Proteins / Q000737:chemistry; D013379:Substrate Specificity
chemical_list: D051660:Intermediate-Conductance Calcium-Activated Potassium Channels; C496923:KCNN4 protein, human; D010716:Phosphatidylinositols; D011993:Recombinant Fusion Proteins; D010744:Phosphoric Monoester Hydrolases; D017027:Protein Tyrosine Phosphatases; D054558:Protein Tyrosine Phosphatases, Non-Receptor; C099588:myotubularin; C061816:phosphatidylinositol-3-phosphatase