title: Phosphatidylinositol-4,5 bisphosphate (PIP(2)) inhibits apo-calmodulin binding to protein 4.1.
abstract: Membrane skeletal protein 4.1R(80) plays a key role in regulation of erythrocyte plasticity. Protein 4.1R(80) interactions with transmembrane proteins, such as glycophorin C (GPC), are regulated by Ca(2+)-saturated calmodulin (Ca(2+)/CaM) through simultaneous binding to a short peptide (pep11; A(264)KKLWKVCVEHHTFFRL) and a serine residue (Ser(185)), both located in the N-terminal 30 kDa FERM domain of 4.1R(80) (H·R30). We have previously demonstrated that CaM binding to H·R30 is Ca(2+)-independent and that CaM binding to H·R30 is responsible for the maintenance of H·R30 β-sheet structure. However, the mechanisms responsible for the regulation of CaM binding to H·R30 are still unknown. To investigate this, we took advantage of similarities and differences in the structure of Coracle, the Drosophila sp. homologue of human 4.1R(80), i.e. conservation of the pep11 sequence but substitution of the Ser(185) residue with an alanine residue. We show that the H·R30 homologue domain of Coracle, Cor30, also binds to CaM in a Ca(2+)-independent manner and that the Ca(2+)/CaM complex does not affect Cor30 binding to the transmembrane protein GPC. We also document that both H·R30 and Cor30 bind to phosphatidylinositol-4,5 bisphosphate (PIP2) and other phospholipid species and that that PIP2 inhibits Ca(2+)-free CaM but not Ca(2+)-saturated CaM binding to Cor30. We conclude that PIP2 may play an important role as a modulator of apo-CaM binding to 4.1R(80) throughout evolution.
authors.affiliation: Center for Geo-Environmental Science, Graduate School of Engineering and Resource Science, Akita University, Akita, Japan; Department of Life Science, Graduate School of Engineering and Resource Science, Akita University, Akita, Japan. Electronic address: nunomura@gipc.akita-u.ac.jp.
authors.forename: Wataru
authors.initials: W
authors.lastname: Nunomura
authors.affiliation: Department of Pathology, University of California at San Francisco, San Francisco, USA.
authors.forename: Philippe
authors.initials: P
authors.lastname: Gascard
authors.affiliation: Department of Life Science, Graduate School of Engineering and Resource Science, Akita University, Akita, Japan.
authors.forename: Hideki
authors.initials: H
authors.lastname: Wakui
authors.affiliation: Department of Biochemistry, Tokyo Women's Medical University, Tokyo, Japan.
authors.forename: Yuichi
authors.initials: Y
authors.lastname: Takakuwa
mesh_terms: D000818:Animals; D001665:Binding Sites; D002118:Calcium / Q000737:chemistry*; D002147:Calmodulin / Q000737:chemistry / Q000378:metabolism*; D003598:Cytoskeletal Proteins / Q000737:chemistry / Q000378:metabolism*; D004330:Drosophila / Q000378:metabolism*; D006801:Humans; D008565:Membrane Proteins / Q000737:chemistry / Q000378:metabolism*; D019269:Phosphatidylinositol 4,5-Diphosphate / Q000737:chemistry / Q000494:pharmacology*; D011485:Protein Binding / Q000187:drug effects
chemical_list: D002147:Calmodulin; D003598:Cytoskeletal Proteins; D008565:Membrane Proteins; D019269:Phosphatidylinositol 4,5-Diphosphate; C028841:erythrocyte membrane band 4.1 protein; D002118:Calcium
keywords: Calmodulin; Coracle; FERM domain; PIP(2); Protein 4.1R