A family of Rab27-binding proteins. Melanophilin links Rab27a and myosin Va function in melanosome transport.
The Rab27a GTPase regulates diverse processes involving lysosome-related organelles, including melanosome motility in melanocytes, and lytic granule release in cytotoxic T lymphocytes. Toward an understanding of Rab27a function, we searched for proteins that interact with Rab27a(GTP) using the yeast two-hybrid system and identified JFC1/Slp1, a protein of unknown function. JFC1/Slp1 and related proteins, including melanophilin, contain a conserved amino-terminal domain similar to the Rab3a-binding domain of Rabphilin-3. We used several methods to demonstrate that this conserved amino-terminal domain is a Rab27-binding domain. We show that this domain interacts directly, and in a GTP-dependent manner with Rab27a. Furthermore, overexpression of this domain in melanocytes results in perinuclear clustering of melanosomes, suggesting that this region is sufficient for interaction with, and perturbation of function of, Rab27a in a physiological context. Thus, we identified a novel family of Rab27-binding proteins. We also show that melanophilin associates with Rab27a and myosin Va on melanosomes in melanocytes, and present evidence that a domain within the carboxyl-terminal region of melanophilin interacts with the carboxyl-terminal tail of the melanocyte-specific splice isoform of myosin Va. Thus, melanophilin can associate simultaneously with activated Rab27a and myosin Va via distinct regions, and serve as a linker between these proteins.
Strom
Molly
M
Department of Cell and Molecular Biology, Division of Biomedical Sciences, Faculty of Medicine, Imperial College, London SW7 2AZ, United Kingdom.
Hume
Alistair N
AN
Tarafder
Abul K
AK
Barkagianni
Eleni
E
Seabra
Miguel C
MC
D048868:Adaptor Proteins, Signal Transducing; D001483:Base Sequence; D002352:Carrier Proteins / Q000378:metabolism*; D017931:DNA Primers; D006801:Humans; D020460:Melanosomes / Q000378:metabolism*; D009218:Myosins / Q000378:metabolism*; D021381:Protein Transport; D020691:rab GTP-Binding Proteins / Q000378:metabolism*; D000075745:rab27 GTP-Binding Proteins
D048868:Adaptor Proteins, Signal Transducing; D002352:Carrier Proteins; D017931:DNA Primers; C492410:MLPH protein, human; D000075745:rab27 GTP-Binding Proteins; C066694:RAB27A protein, human; D009218:Myosins; D020691:rab GTP-Binding Proteins