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Vps27 recruits ESCRT machinery to endosomes during MVB sorting.

Katzmann DJ, Stefan CJ, Babst M, Emr SD - J. Cell Biol. (2003)

Bottom Line: A peptide sequence in this domain, PTVP, is involved in the function of Vps27 in the MVB pathway, the efficient endosomal recruitment of ESCRT-I, and is related to a motif in HIV-1 Gag protein that is capable of interacting with Tsg101, the mammalian homologue of Vps23.We propose that compartmental specificity for the MVB sorting reaction is the result of interactions of Vps27 with phosphatidylinositol 3-phosphate and ubiquitin.Vps27 subsequently recruits/activates ESCRT-I on endosomes, thereby facilitating sorting of ubiquitinated MVB cargoes.

View Article: PubMed Central - PubMed

Affiliation: Department of Cellular and Molecular Medicine, and Howard Hughes Medical Institute, University of California, San Diego School of Medicine, La Jolla, CA 92093-0688, USA.

ABSTRACT
Down-regulation (degradation) of cell surface proteins within the lysosomal lumen depends on the function of the multivesicular body (MVB) sorting pathway. The function of this pathway requires the class E vacuolar protein sorting (Vps) proteins. Of the class E Vps proteins, both the ESCRT-I complex (composed of the class E proteins Vps23, 28, and 37) and Vps27 (mammalian hepatocyte receptor tyrosine kinase substrate, Hrs) have been shown to interact with ubiquitin, a signal for entry into the MVB pathway. We demonstrate that activation of the MVB sorting reaction is dictated largely through interactions between Vps27 and the endosomally enriched lipid species phosphatidylinositol 3-phosphate via the FYVE domain (Fab1, YGL023, Vps27, and EEA1) of Vps27. ESCRT-I then physically binds to Vps27 on endosomal membranes via a domain within the COOH terminus of Vps27. A peptide sequence in this domain, PTVP, is involved in the function of Vps27 in the MVB pathway, the efficient endosomal recruitment of ESCRT-I, and is related to a motif in HIV-1 Gag protein that is capable of interacting with Tsg101, the mammalian homologue of Vps23. We propose that compartmental specificity for the MVB sorting reaction is the result of interactions of Vps27 with phosphatidylinositol 3-phosphate and ubiquitin. Vps27 subsequently recruits/activates ESCRT-I on endosomes, thereby facilitating sorting of ubiquitinated MVB cargoes.

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Model for compartment specification of Ub-dependent sorting into MVB vesicles. The Vps15/Vps34 complex synthesizes PI(3)P on endosomal membranes. The class E Vps protein Vps27 is targeted to PI(3)P- containing endosomal membranes via its FYVE domain (dark blue) where it can bind ubiquitinated MVB cargo via its UIM motifs (yellow). Vps27 subsequently recruits/activates ESCRT-I (orange) on endosomes. Ubiquitinated cargo (such as pCPS) is recognized by ESCRT-I (via the Ub E2 variant domain of Vps23), which initiates cargo entry into MVB vesicles. The action of a number of additional class E Vps proteins (ESCRT-II and ESCRT-III) is required for not only the function of this pathway but also for recruiting the deubiquitinating enzyme to remove Ub from cargo before its entry into invaginating vesicles. The concerted action of these proteins results in the sorting of cargo into the MVB pathway.
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fig7: Model for compartment specification of Ub-dependent sorting into MVB vesicles. The Vps15/Vps34 complex synthesizes PI(3)P on endosomal membranes. The class E Vps protein Vps27 is targeted to PI(3)P- containing endosomal membranes via its FYVE domain (dark blue) where it can bind ubiquitinated MVB cargo via its UIM motifs (yellow). Vps27 subsequently recruits/activates ESCRT-I (orange) on endosomes. Ubiquitinated cargo (such as pCPS) is recognized by ESCRT-I (via the Ub E2 variant domain of Vps23), which initiates cargo entry into MVB vesicles. The action of a number of additional class E Vps proteins (ESCRT-II and ESCRT-III) is required for not only the function of this pathway but also for recruiting the deubiquitinating enzyme to remove Ub from cargo before its entry into invaginating vesicles. The concerted action of these proteins results in the sorting of cargo into the MVB pathway.

Mentions: Based on our data, we propose an ordered reaction in the mechanisms that initiate or activate MVB sorting (Fig. 7). First, Vps27 localization to endosomal membranes requires the production of PI(3)P, as demonstrated by increased cytoplasmic localization of GFP-Vps27 in vps34Δ cells. On endosomes, the PI(3)P effector Vps27 binds ubiquitinated MVB cargo and subsequently recruits and activates ESCRT-I. Activation of Vps27 on membranes may occur through a conformational change triggered by binding PI(3)P and Ub, thereby, exposing a binding site in Vps27 for ESCRT-I. In support of this model, we found that ESCRT-I physically interacts with Vps27 specifically on membranes but not in the cytoplasm (Fig. 4). Upon recruitment/activation by Vps27 on endosomes, ESCRT-I binds ubiquitinated MVB cargo as well. A possible role for the Vps27/ESCRT-I complex may be to facilitate the transfer of MVB cargo to the downstream ESCRT complexes. These later-acting ESCRTs are required for the continued sorting/concentration of MVB cargoes into nascent intraluminal vesicles, and also appear to coordinate the association of accessory factors responsible for such activities as Ub removal, ESCRT dissociation, and vesicle fission (Babst et al., 2002a,b). After assembly of downstream ESCRT machinery, Vps27 may be released to catalyze recruitment of additional ESCRT-I complexes.


Vps27 recruits ESCRT machinery to endosomes during MVB sorting.

Katzmann DJ, Stefan CJ, Babst M, Emr SD - J. Cell Biol. (2003)

Model for compartment specification of Ub-dependent sorting into MVB vesicles. The Vps15/Vps34 complex synthesizes PI(3)P on endosomal membranes. The class E Vps protein Vps27 is targeted to PI(3)P- containing endosomal membranes via its FYVE domain (dark blue) where it can bind ubiquitinated MVB cargo via its UIM motifs (yellow). Vps27 subsequently recruits/activates ESCRT-I (orange) on endosomes. Ubiquitinated cargo (such as pCPS) is recognized by ESCRT-I (via the Ub E2 variant domain of Vps23), which initiates cargo entry into MVB vesicles. The action of a number of additional class E Vps proteins (ESCRT-II and ESCRT-III) is required for not only the function of this pathway but also for recruiting the deubiquitinating enzyme to remove Ub from cargo before its entry into invaginating vesicles. The concerted action of these proteins results in the sorting of cargo into the MVB pathway.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC2172707&req=5

fig7: Model for compartment specification of Ub-dependent sorting into MVB vesicles. The Vps15/Vps34 complex synthesizes PI(3)P on endosomal membranes. The class E Vps protein Vps27 is targeted to PI(3)P- containing endosomal membranes via its FYVE domain (dark blue) where it can bind ubiquitinated MVB cargo via its UIM motifs (yellow). Vps27 subsequently recruits/activates ESCRT-I (orange) on endosomes. Ubiquitinated cargo (such as pCPS) is recognized by ESCRT-I (via the Ub E2 variant domain of Vps23), which initiates cargo entry into MVB vesicles. The action of a number of additional class E Vps proteins (ESCRT-II and ESCRT-III) is required for not only the function of this pathway but also for recruiting the deubiquitinating enzyme to remove Ub from cargo before its entry into invaginating vesicles. The concerted action of these proteins results in the sorting of cargo into the MVB pathway.
Mentions: Based on our data, we propose an ordered reaction in the mechanisms that initiate or activate MVB sorting (Fig. 7). First, Vps27 localization to endosomal membranes requires the production of PI(3)P, as demonstrated by increased cytoplasmic localization of GFP-Vps27 in vps34Δ cells. On endosomes, the PI(3)P effector Vps27 binds ubiquitinated MVB cargo and subsequently recruits and activates ESCRT-I. Activation of Vps27 on membranes may occur through a conformational change triggered by binding PI(3)P and Ub, thereby, exposing a binding site in Vps27 for ESCRT-I. In support of this model, we found that ESCRT-I physically interacts with Vps27 specifically on membranes but not in the cytoplasm (Fig. 4). Upon recruitment/activation by Vps27 on endosomes, ESCRT-I binds ubiquitinated MVB cargo as well. A possible role for the Vps27/ESCRT-I complex may be to facilitate the transfer of MVB cargo to the downstream ESCRT complexes. These later-acting ESCRTs are required for the continued sorting/concentration of MVB cargoes into nascent intraluminal vesicles, and also appear to coordinate the association of accessory factors responsible for such activities as Ub removal, ESCRT dissociation, and vesicle fission (Babst et al., 2002a,b). After assembly of downstream ESCRT machinery, Vps27 may be released to catalyze recruitment of additional ESCRT-I complexes.

Bottom Line: A peptide sequence in this domain, PTVP, is involved in the function of Vps27 in the MVB pathway, the efficient endosomal recruitment of ESCRT-I, and is related to a motif in HIV-1 Gag protein that is capable of interacting with Tsg101, the mammalian homologue of Vps23.We propose that compartmental specificity for the MVB sorting reaction is the result of interactions of Vps27 with phosphatidylinositol 3-phosphate and ubiquitin.Vps27 subsequently recruits/activates ESCRT-I on endosomes, thereby facilitating sorting of ubiquitinated MVB cargoes.

View Article: PubMed Central - PubMed

Affiliation: Department of Cellular and Molecular Medicine, and Howard Hughes Medical Institute, University of California, San Diego School of Medicine, La Jolla, CA 92093-0688, USA.

ABSTRACT
Down-regulation (degradation) of cell surface proteins within the lysosomal lumen depends on the function of the multivesicular body (MVB) sorting pathway. The function of this pathway requires the class E vacuolar protein sorting (Vps) proteins. Of the class E Vps proteins, both the ESCRT-I complex (composed of the class E proteins Vps23, 28, and 37) and Vps27 (mammalian hepatocyte receptor tyrosine kinase substrate, Hrs) have been shown to interact with ubiquitin, a signal for entry into the MVB pathway. We demonstrate that activation of the MVB sorting reaction is dictated largely through interactions between Vps27 and the endosomally enriched lipid species phosphatidylinositol 3-phosphate via the FYVE domain (Fab1, YGL023, Vps27, and EEA1) of Vps27. ESCRT-I then physically binds to Vps27 on endosomal membranes via a domain within the COOH terminus of Vps27. A peptide sequence in this domain, PTVP, is involved in the function of Vps27 in the MVB pathway, the efficient endosomal recruitment of ESCRT-I, and is related to a motif in HIV-1 Gag protein that is capable of interacting with Tsg101, the mammalian homologue of Vps23. We propose that compartmental specificity for the MVB sorting reaction is the result of interactions of Vps27 with phosphatidylinositol 3-phosphate and ubiquitin. Vps27 subsequently recruits/activates ESCRT-I on endosomes, thereby facilitating sorting of ubiquitinated MVB cargoes.

Show MeSH
Related in: MedlinePlus