Syntaxin‐5's flexibility in SNARE pairing supports Golgi functions

Abstract

AbstractDeficiency in the conserved oligomeric Golgi (COG) complex that orchestrates SNARE‐mediated tethering/fusion of vesicles that recycle the Golgi's glycosylation machinery results in severe glycosylation defects. Although two major Golgi v‐SNAREs, GS28/GOSR1, and GS15/BET1L, are depleted in COG‐deficient cells, the complete knockout of GS28 and GS15 only modestly affects Golgi glycosylation, indicating the existence of an adaptation mechanism in Golgi SNARE. Indeed, quantitative mass‐spectrometry analysis of STX5‐interacting proteins revealed two novel Golgi SNARE complexes—STX5/SNAP29/VAMP7 and STX5/VTI1B/STX8/YKT6. These complexes are present in wild‐type cells, but their usage is significantly increased in both GS28‐ and COG‐deficient cells. Upon GS28 deletion, SNAP29 increased its Golgi residency in a STX5‐dependent manner. While STX5 depletion and Retro2‐induced diversion from the Golgi severely affect protein glycosylation, GS28/SNAP29 and GS28/VTI1B double knockouts alter glycosylation similarly to GS28 KO, indicating that a single STX5‐based SNARE complex is sufficient to support Golgi glycosylation. Importantly, co‐depletion of three Golgi SNARE complexes in GS28/SNAP29/VTI1B TKO cells resulted in severe glycosylation defects and a reduced capacity for glycosylation enzyme retention at the Golgi. This study demonstrates the remarkable plasticity in SXT5‐mediated membrane trafficking, uncovering a novel adaptive response to the failure of canonical intra‐Golgi vesicle tethering/fusion machinery.