title: A novel binding protein composed of homophilic tetramer exhibits unique properties for the small GTPase Rab5.
abstract: 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.
authors.affiliation: Department of Physiological Chemistry, Graduate School of Pharmaceutical Sciences, University of Tokyo, Tokyo 113-0033, Japan.
authors.forename: Kota
authors.initials: K
authors.lastname: Saito
authors.forename: Jun
authors.initials: J
authors.lastname: Murai
authors.forename: Hiroaki
authors.initials: H
authors.lastname: Kajiho
authors.forename: Kenji
authors.initials: K
authors.lastname: Kontani
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Kurosu
authors.forename: Toshiaki
authors.initials: T
authors.lastname: Katada
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001665:Binding Sites; D015152:Blotting, Northern; D019556:COS Cells; D002352:Carrier Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D002522:Chlorocebus aethiops; D003001:Cloning, Molecular; D015723:Gene Library; D020662:Guanine Nucleotide Exchange Factors; D016244:Guanosine 5'-O-(3-Thiotriphosphate) / Q000378:metabolism; D006153:Guanosine Diphosphate / Q000378:metabolism; D006160:Guanosine Triphosphate / Q000378:metabolism; D006367:HeLa Cells; D006801:Humans; D007700:Kinetics; D007962:Leukocytes; D008969:Molecular Sequence Data; D011994:Recombinant Proteins / Q000737:chemistry / Q000378:metabolism; D012441:Saccharomyces cerevisiae / Q000235:genetics; D016415:Sequence Alignment; D017386:Sequence Homology, Amino Acid; D014162:Transfection; D020696:rab5 GTP-Binding Proteins / Q000737:chemistry* / Q000378:metabolism*
chemical_list: D002352:Carrier Proteins; D020662:Guanine Nucleotide Exchange Factors; C447829:RIN2 protein, human; D011994:Recombinant Proteins; D006153:Guanosine Diphosphate; D016244:Guanosine 5'-O-(3-Thiotriphosphate); D006160:Guanosine Triphosphate; D020696:rab5 GTP-Binding Proteins