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Published on: May 12, 2023
Rft1 catalyzes lipid-linked oligosaccharide translocation across the ER membrane
Shuai Chen1,2,3, Cai-Xia Pei4,5, Si Xu1
1Key Laboratory of Carbohydrate Chemistry and Biotechnology, Ministry of Education, School of Biotechnology, Jiangnan University, Wuxi, China.
Researchers confirm Rft1 as the enzyme responsible for flipping Man5GlcNAc2-PP-Dol (M5GN2-PP-Dol) across the endoplasmic reticulum membrane. This resolves a long-standing controversy regarding the M5GN2-PP-Dol ER flippase in protein glycosylation.
Area of Science:
- Biochemistry
- Molecular Biology
- Cell Biology
Background:
- Eukaryotic N-linked glycosylation begins with oligosaccharide assembly on a lipid carrier in the ER.
- Man5GlcNAc2-PP-Dol (M5GN2-PP-Dol) is synthesized on the cytoplasmic face and must be translocated to the ER lumen.
- The role of Rft1 in M5GN2-PP-Dol translocation has been debated due to conflicting in vivo and in vitro data.
Purpose of the Study:
- To resolve the controversy surrounding Rft1's function in M5GN2-PP-Dol translocation.
- To biochemically characterize the M5GN2-PP-Dol ER flippase.
- To establish a reconstituted in vitro system for studying M5GN2-PP-Dol translocation.
Main Methods:
- Development of a reconstituted in vitro assay for M5GN2-PP-Dol translocation.
- Purification of Rft1 protein.
- Biochemical characterization of Rft1's enzymatic activity and substrate specificity.
- Analysis of rft1∆ (Rft1 deletion) phenotypes.
Main Results:
- Purified Rft1 directly catalyzes the translocation of M5GN2-PP-Dol across the lipid bilayer in vitro.
- Rft1 exhibits substrate selectivity for M5GN2-PP-Dol.
- In vitro results align with in vivo genetic data, confirming Rft1's flippase activity.
- The study provides definitive evidence for Rft1's role.
Conclusions:
- Rft1 is confirmed as the M5GN2-PP-Dol ER flippase.
- This resolves a two-decade-old controversy regarding the molecular mechanism of oligosaccharide translocation.
- The findings clarify a critical step in the eukaryotic N-linked glycosylation pathway.
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