SNARE chaperone Sly1 directly mediates close-range vesicle tethering

Area of Science:

• Cell Biology
• Molecular Biology
• Membrane Trafficking

Background:

• Sly1 is an essential Golgi protein and a member of the Sec1/mammalian Unc-18 (SM) family of SNARE chaperones.
• Sly1 was identified via gain-of-function mutations that bypass the need for various vesicle tethering factors.

Purpose of the Study:

• To investigate the mechanism by which Sly1 functions as a tether and bypasses other tethering factors.
• To elucidate the role of a conserved loop in Sly1's function and regulation.

Main Methods:

• Genetic analyses in yeast.
• Chemically defined reconstitution of ER-Golgi fusion.
• Biochemical assays to study membrane binding and protein interactions.

Main Results:

• A conserved loop in Sly1 is both autoinhibitory and a positive effector.
• An amphipathic helix within this loop binds to high-curvature membranes.
• Membrane binding relieves Sly1 autoinhibition and enables direct vesicle tethering to Qa-SNAREs.
• The SLY1-20 mutation's ability to bypass tethering factors depends on Sly1's tethering activity.

Conclusions:

• Sly1 directly tethers vesicles to target organelles via its membrane-binding loop.
• Long-range tethers likely hand off vesicles to Sly1 for close-range tethering and fusion initiation.
• This mechanism is crucial for vesicle fusion in the early secretory pathway.