title: Rabaptin5 is recruited to endosomes by Rab4 and Rabex5 to regulate endosome maturation.
abstract: Rab GTPases control membrane identity, fusion and transport by interaction with effector proteins. Effectors that influence the activation-inactivation cycle of their own or other Rab proteins contribute to the timely conversion of Rab membrane identities. Rab5 and its effector rabaptin5 (Rbpt5, also known as RABEP1) are generally considered the prime example for a positive-feedback loop in which Rab5-GTP recruits Rbpt5 in complex with Rabex5 (also known as RABGEF1), the GDP/GTP exchange factor of Rab5, to early endosomes, thus maintaining the Rab5 membrane identity. By deletion analysis, we found that the membrane recruitment of Rabaptin5 required binding to Rab4 and Rabex5, but not Rab5. Deletion of either one of the two Rab5-binding domains or silencing of Rab5 expression did not affect Rabaptin5 recruitment, but produced giant endosomes with early and late endosomal characteristics. The results contradict the model of feedback activation of Rab5 and instead indicate that Rbpt5 is recruited by both Rabex5 recognizing ubiquitylated cargo and by Rab4 to activate Rab5 in a feed-forward manner.
authors.affiliation: Biozentrum, University of Basel, Klingelbergstrasse 70, Basel CH-4056, Switzerland.
authors.forename: Simone
authors.initials: S
authors.lastname: Kälin
authors.affiliation: Biozentrum, University of Basel, Klingelbergstrasse 70, Basel CH-4056, Switzerland.
authors.forename: David T
authors.initials: DT
authors.lastname: Hirschmann
authors.affiliation: Biozentrum, University of Basel, Klingelbergstrasse 70, Basel CH-4056, Switzerland.
authors.forename: Dominik P
authors.initials: DP
authors.lastname: Buser
authors.affiliation: Biozentrum, University of Basel, Klingelbergstrasse 70, Basel CH-4056, Switzerland martin.spiess@unibas.ch.
authors.forename: Martin
authors.initials: M
authors.lastname: Spiess
mesh_terms: D045744:Cell Line, Tumor; D011992:Endosomes / Q000201:enzymology / Q000378:metabolism*; D020662:Guanine Nucleotide Exchange Factors / Q000378:metabolism*; D006367:HeLa Cells; D006801:Humans; D017434:Protein Structure, Tertiary; D025801:Ubiquitin / Q000378:metabolism; D033921:Vesicular Transport Proteins / Q000378:metabolism*; D020695:rab4 GTP-Binding Proteins / Q000378:metabolism*
chemical_list: D020662:Guanine Nucleotide Exchange Factors; C097227:RABEP1 protein, human; C108382:RABGEF1 protein, human; D025801:Ubiquitin; D033921:Vesicular Transport Proteins; D020695:rab4 GTP-Binding Proteins
keywords: Rab GTPase; Rabaptin5; Rabex5