Ubiquitin binding and conjugation regulate the recruitment of Rabex-5 to early endosomes |
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Authors: | Mattera Rafael Bonifacino Juan S |
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Institution: | Cell Biology and Metabolism Program, Eunice Kennedy Shriver National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, MD 20892, USA. |
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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. |
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Keywords: | endosomes Rabaptin-5 Rabex-5 RabGEF1 ubiquitin |
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