biostudies-literatureDuan MUniversity of WashingtonMedical Research CouncilNational Institutes of HealthNational Institute of General Medical SciencesNIGMS NIH HHSNIH HHSe202001032https://www.ebi.ac.uk/biostudies/studies/S-EPMC10943277biostudies-literatureUnknown223(6)The essential Golgi protein Sly1 is a member of the Sec1/mammalian Unc-18 (SM) family of SNARE chaperones. Sly1 was originally identified through remarkable gain-of-function alleles that bypass requirements for diverse vesicle tethering factors. Employing genetic analyses and chemically defined reconstitutions of ER-Golgi fusion, we discovered that a loop conserved among Sly1 family members is not only autoinhibitory but also acts as a positive effector. An amphipathic lipid packing sensor (ALPS)-like helix within the loop directly binds high-curvature membranes. Membrane binding is required for relief of Sly1 autoinhibition and also allows Sly1 to directly tether incoming vesicles to the Qa-SNARE on the target organelle. The SLY1-20 mutation bypasses requirements for diverse tethering factors but loses this ability if the tethering activity is impaired. We propose that long-range tethers, including Golgins and multisubunit tethering complexes, hand off vesicles to Sly1, which then tethers at close range to initiate trans-SNARE complex assembly and fusion in the early secretory pathway.The Journal of cell biologySNARE chaperone Sly1 directly mediates close-range vesicle tethering.PMC10943277R01 GM130644T34 GM083883MC_UP_1201/10R01 GM077349T32 GM007270Nattermann ULin ADuan MMiller EAMima JPlemel RLDelgado BMTakenaka TNickerson DPMerz AJfalseSNARE chaperone Sly1 directly mediates close-range vesicle tethering.The essential Golgi protein Sly1 is a member of the Sec1/mammalian Unc-18 (SM) family of SNARE chaperones. Sly1 was originally identified through remarkable gain-of-function alleles that bypass requirements for diverse vesicle tethering factors. Employing genetic analyses and chemically defined reconstitutions of ER-Golgi fusion, we discovered that a loop conserved among Sly1 family members is not only autoinhibitory but also acts as a positive effector. An amphipathic lipid packing sensor (ALPS)-like helix within the loop directly binds high-curvature membranes. Membrane binding is required for relief of Sly1 autoinhibition and also allows Sly1 to directly tether incoming vesicles to the Qa-SNARE on the target organelle. The SLY1-20 mutation bypasses requirements for diverse tethering factors but loses this ability if the tethering activity is impaired. We propose that long-range tethers, including Golgins and multisubunit tethering complexes, hand off vesicles to Sly1, which then tethers at close range to initiate trans-SNARE complex assembly and fusion in the early secretory pathway.2024-01-01T00:00:00Z2024 Jun2026-06-01T16:31:50.618Z2025-04-06T19:30:03.813ZS-EPMC109432773847801810.1083/jcb.202001032