Rabenosyn-5, a Novel Rab5 Effector, Is Complexed with Hvps45 and Recruited to Endosomes through a Fyve Finger Domain

Max-Planck-Institute for Molecular Cell Biology and Genetics, 01307 Dresden, Germany.
The Journal of Cell Biology (Impact Factor: 9.83). 11/2000; 151(3):601-12.
Source: PubMed


Rab5 regulates endocytic membrane traffic by specifically recruiting cytosolic effector proteins to their site of action on early endosomal membranes. We have characterized a new Rab5 effector complex involved in endosomal fusion events. This complex includes a novel protein, Rabenosyn-5, which, like the previously characterized Rab5 effector early endosome antigen 1 (EEA1), contains an FYVE finger domain and is recruited in a phosphatidylinositol-3-kinase-dependent fashion to early endosomes. Rabenosyn-5 is complexed to the Sec1-like protein hVPS45. hVPS45 does not interact directly with Rab5, therefore Rabenosyn-5 serves as a molecular link between hVPS45 and the Rab5 GTPase. This property suggests that Rabenosyn-5 is a closer mammalian functional homologue of yeast Vac1p than EEA1. Furthermore, although both EEA1 and Rabenosyn-5 are required for early endosomal fusion, only overexpression of Rabenosyn-5 inhibits cathepsin D processing, suggesting that the two proteins play distinct roles in endosomal trafficking. We propose that Rab5-dependent formation of membrane domains enriched in phosphatidylinositol-3-phosphate has evolved as a mechanism for the recruitment of multiple effector proteins to mammalian early endosomes, and that these domains are multifunctional, depending on the differing activities of the effector proteins recruited.

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    • "e found that DRG2 interacted with Rab5 , indicating that interaction between DRG2 and Rab5 mediates the localization of DRG2 to Rab5 endosomes . Rab5 recruits PI - 3 - kinases in a GTP - dependent manner , resulting in localized synthesis of PI - 3P ( Christoforidis et al . , 1999b ) . In turn , EEA1 ( Simonsen et al . , 1998 ) and Rabenosyn - 5 ( Nielsen et al . , 2000 ) , Rab5 effectors , bind PI3P through the interaction of a FYVE domain in a PI3K - dependent manner . In this study , we also found that , while DRG2 did not colocalize with Rabenosyn - 5 on endosomes , it colocalized and interacted with EEA1 on endosomes . In addition , colocalization and interaction of DRG2 with EEA1 on endosomes wer"
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    • "motor protein complexes). Rab5 has been shown to interact with at least 20 identified proteins through the use of Rab5-GST fusion proteins in affinity chromatography preloaded with either GTP or GDP and after binding to effector molecules, eluted with GDP or GTP, respectively[14]: Rabaptin-5[15], RIN3[16], Rabex-5 GEF[17], Rabenosyn-5[18],[19], Rabankyrin-5[20], EEA1[21], PI-3 kinases hVPS34 and p85α-p110β[22],[23], PI-4, PI-5 phosphatases[24], kinesin type motor proteins for microtubule dependent movement[25], APPL1 and APPL2[26], syntaxin-13[27], GGAs[28], Huntingtin and HAP40[29]. The nature of the function of Rab proteins (cycling between the “on” and “off” state) may make for only transient interactions with effectors, which from an experimental perspective, are difficult to trap. "
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    • "Interestingly, only the combination of both tethers led to significant fusion , suggesting that one cannot substitute for the other. These two tethers also coordinate Rab function with SNARE assembly on early endosomes, because rabenosyn-5 binds the Sec1/Munc18-like Vps45 protein (Nielsen et al. 2000; Morrison et al. 2008), and EEA1 binds "
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