A novel binding protein composed of homophilic tetramer exhibits unique properties for the small GTPase Rab5.

The small GTPase Rab family, which cycles between GTP-bound active and GDP-bound inactive states, plays an important role in membrane trafficking. Among them, Rab5 is involved in early endocytic pathway, and several Rab5-binding proteins have been identified as regulators or effectors to coordinate the docking and fusion processes of endocytic ...
vesicles. We describe a novel binding protein exhibiting unique biochemical properties for Rab5. The Rab5-binding protein enhances GDP-GTP exchange reaction on Rab5 but preferentially interacts with its GTP-bound form. Gel filtration and immunoprecipitation analyses indicate that the Rab5-binding protein functions as a tetramer composed of anti-parallel linkage of two parallel dimers. These results suggest that the newly identified protein may function as an upstream activator and/or downstream effector for Rab5 in endocytic pathway. Possible roles of the quaternary structure have been discussed in terms of the Rab5-mediated signaling.
Mesh Terms:
Amino Acid Sequence, Animals, Binding Sites, Blotting, Northern, COS Cells, Carrier Proteins, Cercopithecus aethiops, Cloning, Molecular, Gene Library, Guanine Nucleotide Exchange Factors, Guanosine 5'-O-(3-Thiotriphosphate), Guanosine Diphosphate, Guanosine Triphosphate, Hela Cells, Humans, Kinetics, Leukocytes, Molecular Sequence Data, Recombinant Proteins, Saccharomyces cerevisiae, Sequence Alignment, Sequence Homology, Amino Acid, Transfection, rab5 GTP-Binding Proteins
J. Biol. Chem.
Date: Feb. 01, 2002
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