title: Ubiquitin binding and conjugation regulate the recruitment of Rabex-5 to early endosomes.
abstract: Rab GTPases and ubiquitination are critical regulators of transmembrane cargo sorting in endocytic and lysosomal targeting pathways. The endosomal protein Rabex-5 intersects these two layers of regulation by being both a guanine nucleotide exchange factor (GEF) for Rab5 and a substrate for ubiquitin (Ub) binding and conjugation. The ability of trafficking machinery components to bind ubiquitinated proteins is known to have a function in cargo sorting. Here, we demonstrate that Ub binding is essential for the recruitment of Rabex-5 from the cytosol to endosomes, independently of its GEF activity and of Rab5. We also show that monoubiquitinated Rabex-5 is enriched in the cytosol. These observations are consistent with a model whereby a cycle of Ub binding and monoubiquitination regulates the association of Rabex-5 with endosomes.
authors.affiliation: Cell Biology and Metabolism Program, Eunice Kennedy Shriver National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, MD 20892, USA.
authors.forename: Rafael
authors.initials: R
authors.lastname: Mattera
authors.forename: Juan S
authors.initials: JS
authors.lastname: Bonifacino
mesh_terms: D000818:Animals; D002417:Cattle; D011992:Endosomes / Q000378:metabolism*; D020662:Guanine Nucleotide Exchange Factors / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D006367:HeLa Cells; D006801:Humans; D008958:Models, Molecular; D011485:Protein Binding; D011487:Protein Conformation; D016271:Proto-Oncogene Proteins c-myc / Q000235:genetics / Q000378:metabolism; D011993:Recombinant Fusion Proteins / Q000235:genetics / Q000378:metabolism; D025801:Ubiquitin / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D033921:Vesicular Transport Proteins / Q000235:genetics / Q000378:metabolism; D020696:rab5 GTP-Binding Proteins / Q000235:genetics / Q000378:metabolism
chemical_list: D020662:Guanine Nucleotide Exchange Factors; D016271:Proto-Oncogene Proteins c-myc; D011993:Recombinant Fusion Proteins; D025801:Ubiquitin; D033921:Vesicular Transport Proteins; D020696:rab5 GTP-Binding Proteins
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