title: Tollip and Tom1 form a complex and recruit ubiquitin-conjugated proteins onto early endosomes.
abstract: Tom1 (target of Myb1) is a protein of unknown function. Tom1 and its relative Tom1L1 have an N-terminal VHS (Vps27p/Hrs/Stam) domain followed by a GAT (GGA and Tom1) domain, both of which are also found in the GGA (Golgi-localizing, gamma-adaptin ear domain homology, ADP-ribosylation factor-binding protein) family of proteins. Although the VHS and GAT domains of GGA proteins bind to transmembrane cargo proteins and the small GTPase ADP-ribosylation factor, respectively, the VHS and GAT domains of Tom1 are unable to interact with these proteins. In this study, we show that the GAT domains of Tom1 and Tom1L1 interact with ubiquitin and Tollip (Toll-interacting protein). Ubiquitin bound the GAT domains of Tom1, Tom1L1, and GGA proteins, whereas Tollip interacted specifically with Tom1 and Tom1L1. Ubiquitin and Tollip bound to an overlapping region of the Tom1-GAT domain in a mutually exclusive manner. Tom1 was predominantly cytosolic when expressed in cells. On the other hand, Tollip was localized on early endosomes and recruited Tom1 and ubiquitinated proteins. These observations suggest that Tollip and Tom1 form a complex and regulate endosomal trafficking of ubiquitinated proteins.
authors.affiliation: Institute of Biological Sciences, University of Tsukuba, Tsukuba, Ibaraki 305-8572, Japan.
authors.forename: Yohei
authors.initials: Y
authors.lastname: Katoh
authors.forename: Yoko
authors.initials: Y
authors.lastname: Shiba
authors.forename: Hiroko
authors.initials: H
authors.lastname: Mitsuhashi
authors.forename: Yuko
authors.initials: Y
authors.lastname: Yanagida
authors.forename: Hiroyuki
authors.initials: H
authors.lastname: Takatsu
authors.forename: Kazuhisa
authors.initials: K
authors.lastname: Nakayama
mesh_terms: D000595:Amino Acid Sequence; D001921:Brain / Q000378:metabolism; D002352:Carrier Proteins / Q000378:metabolism*; D003600:Cytosol / Q000378:metabolism; D018076:DNA, Complementary / Q000378:metabolism; D011992:Endosomes / Q000378:metabolism*; D005982:Glutathione Transferase / Q000378:metabolism; D006367:HeLa Cells; D006801:Humans; D047908:Intracellular Signaling Peptides and Proteins; D008856:Microscopy, Fluorescence; D008954:Models, Biological; D008969:Molecular Sequence Data; D010957:Plasmids / Q000378:metabolism; D011233:Precipitin Tests; D011485:Protein Binding; D017434:Protein Structure, Tertiary; D011506:Proteins / Q000378:metabolism*; D017386:Sequence Homology, Amino Acid; D020798:Two-Hybrid System Techniques; D025801:Ubiquitin / Q000737:chemistry / Q000378:metabolism*
chemical_list: D002352:Carrier Proteins; D018076:DNA, Complementary; D047908:Intracellular Signaling Peptides and Proteins; D011506:Proteins; C410602:TOLLIP protein, human; C120296:TOM1 protein, human; D025801:Ubiquitin; D005982:Glutathione Transferase