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HIV Gag mimics the Tsg101-recruiting activity of the human Hrs protein.

Pornillos O, Higginson DS, Stray KM, Fisher RD, Garrus JE, Payne M, He GP, Wang HE, Morham SG, Sundquist WI - J. Cell Biol. (2003)

Bottom Line: Importantly, Hrs222-777 can recruit Tsg101 and rescue the budding of virus-like Gag particles that are missing native late domains.These observations indicate that Hrs normally functions to recruit Tsg101 to the endosomal membrane.HIV-1 Gag apparently mimics this Hrs activity, and thereby usurps Tsg101 and other components of the MVB vesicle fission machinery to facilitate viral budding.

View Article: PubMed Central - PubMed

Affiliation: Department of Biochemistry, University of Utah, School of Medicine, Salt Lake City, UT 84132, USA. wes@biochem.utah.edu

ABSTRACT
The HIV-1 Gag protein recruits the cellular factor Tsg101 to facilitate the final stages of virus budding. A conserved P(S/T)AP tetrapeptide motif within Gag (the "late domain") binds directly to the NH2-terminal ubiquitin E2 variant (UEV) domain of Tsg101. In the cell, Tsg101 is required for biogenesis of vesicles that bud into the lumen of late endosomal compartments called multivesicular bodies (MVBs). However, the mechanism by which Tsg101 is recruited from the cytoplasm onto the endosomal membrane has not been known. Now, we report that Tsg101 binds the COOH-terminal region of the endosomal protein hepatocyte growth factor-regulated tyrosine kinase substrate (Hrs; residues 222-777). This interaction is mediated, in part, by binding of the Tsg101 UEV domain to the Hrs 348PSAP351 motif. Importantly, Hrs222-777 can recruit Tsg101 and rescue the budding of virus-like Gag particles that are missing native late domains. These observations indicate that Hrs normally functions to recruit Tsg101 to the endosomal membrane. HIV-1 Gag apparently mimics this Hrs activity, and thereby usurps Tsg101 and other components of the MVB vesicle fission machinery to facilitate viral budding.

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Models for Tsg101 recruitment and activation during MVB and HIV budding. (A) Model illustrating sites of Tsg101/Hrs interaction and a possible activation mechanism for Tsg101 (see text for details). Note that our data allow the possibility that other proteins might bridge or contribute to the interaction between the COOH-terminal regions of Tsg101 and Hrs. (B) Model illustrating how HIV Gag mimics the Tsg101-recruiting function of Hrs and redirects Tsg101 and the ESCRT-I complex to the plasma membrane to facilitate viral budding.
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fig7: Models for Tsg101 recruitment and activation during MVB and HIV budding. (A) Model illustrating sites of Tsg101/Hrs interaction and a possible activation mechanism for Tsg101 (see text for details). Note that our data allow the possibility that other proteins might bridge or contribute to the interaction between the COOH-terminal regions of Tsg101 and Hrs. (B) Model illustrating how HIV Gag mimics the Tsg101-recruiting function of Hrs and redirects Tsg101 and the ESCRT-I complex to the plasma membrane to facilitate viral budding.

Mentions: The use of multiple contact sites could simply serve to increase the affinity and specificity of the Hrs/Tsg101 interaction. However, an attractive alternative model is that the downstream Hrs site serves primarily to recruit Tsg101 to sites of vesicle budding, whereas the Hrs PSAP element serves primarily as the switch that “activates” Tsg101 for ESCRT-II and/or MVB cargo binding (or for other essential events in MVB biogenesis). In this model, we envision that the soluble cytoplasmic ESCRT-I protein may exist primarily in an autoinhibited conformation in which the Tsg101 UEV domain binds its own PTAP element (i.e., in cis; Fig. 7 A). Hrs binding could then drive a conformational change in which the Tsg101 UEV domain switches to bind the PSAP element of Hrs (i.e., in trans). This activation event might also involve the ubiquitin-binding site on the UEV domain interacting with ubiquitin modifications on protein cargos, which would provide a cooperative binding mechanism for insuring that activation occurs only in the presence of both Hrs and ubiquitylated protein cargos. Although this model remains to be tested rigorously, we note that analogous autoinhibition/conformational switching mechanisms are used by other classes of proteins, such as protein kinases, to create directionality in other cellular pathways (Francis et al., 2002; Pellicena and Miller, 2002).


HIV Gag mimics the Tsg101-recruiting activity of the human Hrs protein.

Pornillos O, Higginson DS, Stray KM, Fisher RD, Garrus JE, Payne M, He GP, Wang HE, Morham SG, Sundquist WI - J. Cell Biol. (2003)

Models for Tsg101 recruitment and activation during MVB and HIV budding. (A) Model illustrating sites of Tsg101/Hrs interaction and a possible activation mechanism for Tsg101 (see text for details). Note that our data allow the possibility that other proteins might bridge or contribute to the interaction between the COOH-terminal regions of Tsg101 and Hrs. (B) Model illustrating how HIV Gag mimics the Tsg101-recruiting function of Hrs and redirects Tsg101 and the ESCRT-I complex to the plasma membrane to facilitate viral budding.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC2172688&req=5

fig7: Models for Tsg101 recruitment and activation during MVB and HIV budding. (A) Model illustrating sites of Tsg101/Hrs interaction and a possible activation mechanism for Tsg101 (see text for details). Note that our data allow the possibility that other proteins might bridge or contribute to the interaction between the COOH-terminal regions of Tsg101 and Hrs. (B) Model illustrating how HIV Gag mimics the Tsg101-recruiting function of Hrs and redirects Tsg101 and the ESCRT-I complex to the plasma membrane to facilitate viral budding.
Mentions: The use of multiple contact sites could simply serve to increase the affinity and specificity of the Hrs/Tsg101 interaction. However, an attractive alternative model is that the downstream Hrs site serves primarily to recruit Tsg101 to sites of vesicle budding, whereas the Hrs PSAP element serves primarily as the switch that “activates” Tsg101 for ESCRT-II and/or MVB cargo binding (or for other essential events in MVB biogenesis). In this model, we envision that the soluble cytoplasmic ESCRT-I protein may exist primarily in an autoinhibited conformation in which the Tsg101 UEV domain binds its own PTAP element (i.e., in cis; Fig. 7 A). Hrs binding could then drive a conformational change in which the Tsg101 UEV domain switches to bind the PSAP element of Hrs (i.e., in trans). This activation event might also involve the ubiquitin-binding site on the UEV domain interacting with ubiquitin modifications on protein cargos, which would provide a cooperative binding mechanism for insuring that activation occurs only in the presence of both Hrs and ubiquitylated protein cargos. Although this model remains to be tested rigorously, we note that analogous autoinhibition/conformational switching mechanisms are used by other classes of proteins, such as protein kinases, to create directionality in other cellular pathways (Francis et al., 2002; Pellicena and Miller, 2002).

Bottom Line: Importantly, Hrs222-777 can recruit Tsg101 and rescue the budding of virus-like Gag particles that are missing native late domains.These observations indicate that Hrs normally functions to recruit Tsg101 to the endosomal membrane.HIV-1 Gag apparently mimics this Hrs activity, and thereby usurps Tsg101 and other components of the MVB vesicle fission machinery to facilitate viral budding.

View Article: PubMed Central - PubMed

Affiliation: Department of Biochemistry, University of Utah, School of Medicine, Salt Lake City, UT 84132, USA. wes@biochem.utah.edu

ABSTRACT
The HIV-1 Gag protein recruits the cellular factor Tsg101 to facilitate the final stages of virus budding. A conserved P(S/T)AP tetrapeptide motif within Gag (the "late domain") binds directly to the NH2-terminal ubiquitin E2 variant (UEV) domain of Tsg101. In the cell, Tsg101 is required for biogenesis of vesicles that bud into the lumen of late endosomal compartments called multivesicular bodies (MVBs). However, the mechanism by which Tsg101 is recruited from the cytoplasm onto the endosomal membrane has not been known. Now, we report that Tsg101 binds the COOH-terminal region of the endosomal protein hepatocyte growth factor-regulated tyrosine kinase substrate (Hrs; residues 222-777). This interaction is mediated, in part, by binding of the Tsg101 UEV domain to the Hrs 348PSAP351 motif. Importantly, Hrs222-777 can recruit Tsg101 and rescue the budding of virus-like Gag particles that are missing native late domains. These observations indicate that Hrs normally functions to recruit Tsg101 to the endosomal membrane. HIV-1 Gag apparently mimics this Hrs activity, and thereby usurps Tsg101 and other components of the MVB vesicle fission machinery to facilitate viral budding.

Show MeSH
Related in: MedlinePlus