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TRAPP stimulates guanine nucleotide exchange on Ypt1p
W Wang1, M Sacher, S Ferro-Novick
1Howard Hughes Medical Institute and the Department of Cell Biology Yale University School of Medicine, New Haven, Connecticut 06519-1418, USA.
The Journal of Cell Biology
|October 19, 2000
Summary
The TRAPP complex binds to the nucleotide-free form of Ypt1p, a small GTP-binding protein. This interaction activates Ypt1p at the Golgi, mediating ER-to-Golgi vesicle targeting.
Area of Science:
- Cell Biology
- Molecular Biology
- Biochemistry
Background:
- The secretory pathway involves precise membrane trafficking, with ER-to-Golgi transport being a critical early step.
- The TRAPP complex, located on the early Golgi, is known to mediate vesicle targeting.
- Ypt1p, a small GTP-binding protein, regulates membrane traffic and has known genetic interactions with TRAPP subunits Bet3p and Bet5p.
Purpose of the Study:
- To investigate the interaction between the TRAPP complex and Ypt1p.
- To elucidate the role of TRAPP in regulating Ypt1p activity.
- To understand the mechanism of ER-to-Golgi vesicle targeting.
Main Methods:
- Biochemical assays to study TRAPP binding to Ypt1p.
- Analysis of Ypt1p nucleotide exchange in TRAPP mutants.
- Purification of the TRAPP complex for in vitro studies.
Main Results:
- TRAPP preferentially binds to the nucleotide-free form of Ypt1p.
- Mutants with defects in TRAPP subunits show temperature-sensitive defects in displacing GDP from Ypt1p.
- Purified TRAPP complex accelerates nucleotide exchange on Ypt1p.
Conclusions:
- TRAPP functions as a guanine nucleotide exchange factor (GEF) for Ypt1p.
- Ypt1p is activated by TRAPP upon arrival at the Golgi.
- This activation is crucial for the targeting of ER-to-Golgi transport vesicles.