title: Melanophilin directly links Rab27a and myosin Va through its distinct coiled-coil regions.
abstract: Rab GTPases regulate the membrane transport pathways by recruiting their specific effector proteins. Melanophilin, a putative Rab effector, has recently been identified as a gene that is mutated in leaden mice, in which peripheral localization of melanosomes is impaired in melanocytes. Genetic studies suggest that three coat-color mutation genes, dilute (MyoVa(d)), ashen (Rab27a(ash)), and leaden (Mlph(ln)), act in the same or overlapping pathways. Here we have cloned and characterized a human melanophilin homolog, which belongs to the rabphilin3/granuphilin-like Rab effector family. Cosedimentation assays using recombinant proteins reveal that melanophilin directly binds to Rab27a and myosin Va through its N-terminal and its first C-terminal coiled-coil region, respectively. Moreover, we show that Rab27a, melanophilin, and myosin Va form a ternary complex in the human melanocyte cell line HMV-II. These findings suggest that melanophilin has a role in bridging Rab27a on melanosomes and myosin Va on actin filaments during melanosome transport. We also propose that the Rab-binding region conserved in a novel rabphilin3/granuphilin-like Rab effector family constitutes an alpha-helix-based coiled-coil structure.
authors.affiliation: Laboratory of Gene Engineering, Institute for Molecular and Cellular Regulation, Gunma University, 3-39-15 Showa-machi, Maebashi, Gunma, Japan.
authors.forename: Kazuaki
authors.initials: K
authors.lastname: Nagashima
authors.forename: Seiji
authors.initials: S
authors.lastname: Torii
authors.forename: Zhaohong
authors.initials: Z
authors.lastname: Yi
authors.forename: Michihiro
authors.initials: M
authors.lastname: Igarashi
authors.forename: Koichi
authors.initials: K
authors.lastname: Okamoto
authors.forename: Toshiyuki
authors.initials: T
authors.lastname: Takeuchi
authors.forename: Tetsuro
authors.initials: T
authors.lastname: Izumi
mesh_terms: D008841:Actin Cytoskeleton / Q000378:metabolism; D048868:Adaptor Proteins, Signal Transducing; D001665:Binding Sites; D001692:Biological Transport / Q000502:physiology; D002352:Carrier Proteins / Q000378:metabolism*; D006801:Humans; D046911:Macromolecular Substances; D008544:Melanocytes / Q000378:metabolism*; D008545:Melanoma; D020460:Melanosomes / Q000378:metabolism; D008969:Molecular Sequence Data; D024701:Myosin Type V / Q000737:chemistry / Q000378:metabolism*; D011487:Protein Conformation; D016415:Sequence Alignment; D014407:Tumor Cells, Cultured; D020691:rab GTP-Binding Proteins / Q000737:chemistry / Q000378:metabolism*; D000075745:rab27 GTP-Binding Proteins
chemical_list: D048868:Adaptor Proteins, Signal Transducing; D002352:Carrier Proteins; C492410:MLPH protein, human; D046911:Macromolecular Substances; D000075745:rab27 GTP-Binding Proteins; D024701:Myosin Type V; C066694:RAB27A protein, human; D020691:rab GTP-Binding Proteins