Turnover of Variant Surface Glycoprotein in <named-content content-type="genus-species">Trypanosoma brucei</named-content> Is a Bimodal Process
ABSTRACT African trypanosomes utilize glycosylphosphatidylinositol (GPI)-anchored variant surface glycoprotein (VSG) to evade the host immune system. VSG turnover is thought to be mediated via cleavage of the GPI anchor by endogenous GPI-specific phospholipase C (GPI-PLC). However, GPI-PLC is topolo...
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American Society for Microbiology
2021
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oai:doaj.org-article:bf9bd0020fb4404db69135c5e3a5c6f52021-11-10T18:37:52ZTurnover of Variant Surface Glycoprotein in <named-content content-type="genus-species">Trypanosoma brucei</named-content> Is a Bimodal Process10.1128/mBio.01725-212150-7511https://doaj.org/article/bf9bd0020fb4404db69135c5e3a5c6f52021-08-01T00:00:00Zhttps://journals.asm.org/doi/10.1128/mBio.01725-21https://doaj.org/toc/2150-7511ABSTRACT African trypanosomes utilize glycosylphosphatidylinositol (GPI)-anchored variant surface glycoprotein (VSG) to evade the host immune system. VSG turnover is thought to be mediated via cleavage of the GPI anchor by endogenous GPI-specific phospholipase C (GPI-PLC). However, GPI-PLC is topologically sequestered from VSG substrates in intact cells. Recently, A. J. Szempruch, S. E. Sykes, R. Kieft, L. Dennison, et al. (Cell 164:246–257, 2016, https://doi.org/10.1016/j.cell.2015.11.051) demonstrated the release of nanotubes that septate to form free VSG+ extracellular vesicles (EVs). Here, we evaluated the relative contributions of GPI hydrolysis and EV formation to VSG turnover in wild-type (WT) and GPI-PLC null cells. The turnover rate of VSG was consistent with prior measurements (half-life [t1/2] of ∼26 h) but dropped significantly in the absence of GPI-PLC (t1/2 of ∼36 h). Ectopic complementation restored normal turnover rates, confirming the role of GPI-PLC in turnover. However, physical characterization of shed VSG in WT cells indicated that at least 50% is released directly from cell membranes with intact GPI anchors. Shedding of EVs plays an insignificant role in total VSG turnover in both WT and null cells. In additional studies, GPI-PLC was found to have no role in biosynthetic and endocytic trafficking to the lysosome but did influence the rate of receptor-mediated endocytosis. These results indicate that VSG turnover is a bimodal process involving both direct shedding and GPI hydrolysis. IMPORTANCE African trypanosomes, the protozoan agent of human African trypanosomaisis, avoid the host immune system by switching expression of the variant surface glycoprotein (VSG). VSG is a long-lived protein that has long been thought to be turned over by hydrolysis of its glycolipid membrane anchor. Recent work demonstrating the shedding of VSG-containing extracellular vesicles has led us to reinvestigate the mode of VSG turnover. We found that VSG is shed in part by glycolipid hydrolysis but also in approximately equal part by direct shedding of protein with intact lipid anchors. Shedding of exocytic vesicles made a very minor contribution to overall VSG turnover. These results indicate that VSG turnover is a bimodal process and significantly alter our understanding of the “life cycle” of this critical virulence factor.Paige GarrisonUmaer KhanMichael CiprianoPeter J. BushJacquelyn McDonaldAakash SurPeter J. MylerTerry K. SmithStephen L. HajdukJames D. BangsAmerican Society for Microbiologyarticletrypanosomevariant surface glycoproteinglycosylphosphatidylinositolglycosylphosphatidylinositol-specific phospholipase Cextracellular vesiclesMicrobiologyQR1-502ENmBio, Vol 12, Iss 4 (2021) |
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DOAJ |
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EN |
| topic |
trypanosome variant surface glycoprotein glycosylphosphatidylinositol glycosylphosphatidylinositol-specific phospholipase C extracellular vesicles Microbiology QR1-502 |
| spellingShingle |
trypanosome variant surface glycoprotein glycosylphosphatidylinositol glycosylphosphatidylinositol-specific phospholipase C extracellular vesicles Microbiology QR1-502 Paige Garrison Umaer Khan Michael Cipriano Peter J. Bush Jacquelyn McDonald Aakash Sur Peter J. Myler Terry K. Smith Stephen L. Hajduk James D. Bangs Turnover of Variant Surface Glycoprotein in <named-content content-type="genus-species">Trypanosoma brucei</named-content> Is a Bimodal Process |
| description |
ABSTRACT African trypanosomes utilize glycosylphosphatidylinositol (GPI)-anchored variant surface glycoprotein (VSG) to evade the host immune system. VSG turnover is thought to be mediated via cleavage of the GPI anchor by endogenous GPI-specific phospholipase C (GPI-PLC). However, GPI-PLC is topologically sequestered from VSG substrates in intact cells. Recently, A. J. Szempruch, S. E. Sykes, R. Kieft, L. Dennison, et al. (Cell 164:246–257, 2016, https://doi.org/10.1016/j.cell.2015.11.051) demonstrated the release of nanotubes that septate to form free VSG+ extracellular vesicles (EVs). Here, we evaluated the relative contributions of GPI hydrolysis and EV formation to VSG turnover in wild-type (WT) and GPI-PLC null cells. The turnover rate of VSG was consistent with prior measurements (half-life [t1/2] of ∼26 h) but dropped significantly in the absence of GPI-PLC (t1/2 of ∼36 h). Ectopic complementation restored normal turnover rates, confirming the role of GPI-PLC in turnover. However, physical characterization of shed VSG in WT cells indicated that at least 50% is released directly from cell membranes with intact GPI anchors. Shedding of EVs plays an insignificant role in total VSG turnover in both WT and null cells. In additional studies, GPI-PLC was found to have no role in biosynthetic and endocytic trafficking to the lysosome but did influence the rate of receptor-mediated endocytosis. These results indicate that VSG turnover is a bimodal process involving both direct shedding and GPI hydrolysis. IMPORTANCE African trypanosomes, the protozoan agent of human African trypanosomaisis, avoid the host immune system by switching expression of the variant surface glycoprotein (VSG). VSG is a long-lived protein that has long been thought to be turned over by hydrolysis of its glycolipid membrane anchor. Recent work demonstrating the shedding of VSG-containing extracellular vesicles has led us to reinvestigate the mode of VSG turnover. We found that VSG is shed in part by glycolipid hydrolysis but also in approximately equal part by direct shedding of protein with intact lipid anchors. Shedding of exocytic vesicles made a very minor contribution to overall VSG turnover. These results indicate that VSG turnover is a bimodal process and significantly alter our understanding of the “life cycle” of this critical virulence factor. |
| format |
article |
| author |
Paige Garrison Umaer Khan Michael Cipriano Peter J. Bush Jacquelyn McDonald Aakash Sur Peter J. Myler Terry K. Smith Stephen L. Hajduk James D. Bangs |
| author_facet |
Paige Garrison Umaer Khan Michael Cipriano Peter J. Bush Jacquelyn McDonald Aakash Sur Peter J. Myler Terry K. Smith Stephen L. Hajduk James D. Bangs |
| author_sort |
Paige Garrison |
| title |
Turnover of Variant Surface Glycoprotein in <named-content content-type="genus-species">Trypanosoma brucei</named-content> Is a Bimodal Process |
| title_short |
Turnover of Variant Surface Glycoprotein in <named-content content-type="genus-species">Trypanosoma brucei</named-content> Is a Bimodal Process |
| title_full |
Turnover of Variant Surface Glycoprotein in <named-content content-type="genus-species">Trypanosoma brucei</named-content> Is a Bimodal Process |
| title_fullStr |
Turnover of Variant Surface Glycoprotein in <named-content content-type="genus-species">Trypanosoma brucei</named-content> Is a Bimodal Process |
| title_full_unstemmed |
Turnover of Variant Surface Glycoprotein in <named-content content-type="genus-species">Trypanosoma brucei</named-content> Is a Bimodal Process |
| title_sort |
turnover of variant surface glycoprotein in <named-content content-type="genus-species">trypanosoma brucei</named-content> is a bimodal process |
| publisher |
American Society for Microbiology |
| publishDate |
2021 |
| url |
https://doaj.org/article/bf9bd0020fb4404db69135c5e3a5c6f5 |
| work_keys_str_mv |
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