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FEBS Lett. 2002 Apr 24;517(1-3):233-8.

Melanophilin directly links Rab27a and myosin Va through its distinct coiled-coil regions.

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Laboratory of Gene Engineering, Institute for Molecular and Cellular Regulation, Gunma University, 3-39-15 Showa-machi, Maebashi, Gunma, Japan.


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.

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