A tethering complex dimer catalyzes trans-SNARE complex formation in intracellular membrane fusion

Area of Science:

• Cell Biology
• Membrane Trafficking
• Molecular Mechanisms

Background:

• Soluble NSF Attachment Protein REceptor (SNARE) complexes mediate membrane fusion, a vital process in the endomembrane system.
• Trans-SNARE complexes, formed by SNAREs from opposing membranes, are critical intermediates in membrane fusion.
• The precise mechanisms and topology of trans-SNARE complex formation in vivo are not fully understood.

Purpose of the Study:

• To elucidate the mechanistic details and topological preferences of trans-SNARE complex formation in a physiological system.
• To identify factors beyond SNAREs that regulate trans-SNARE complex assembly during membrane fusion.

Main Methods:

• Studies were conducted on native yeast vacuoles.
• Investigated the roles of SNAREs, tethering complexes, and Rab GTPases in membrane fusion.

Main Results:

• SNARE proteins alone are insufficient for trans-SNARE complex formation.
• Tethering complexes and Rab GTPases are necessary additional factors.
• A dimer of the HOPS (Homotypic Vacuolar Protein Sorting) tethering complex catalyzes the formation of a topologically defined QbQcR-Qa trans-SNARE complex in a Rab GTPase-dependent manner.

Conclusions:

• HOPS tethering complex dimers play a crucial role in catalyzing SNARE complex formation.
• Rab GTPase-dependent catalysis by HOPS ensures the formation of a specific trans-SNARE complex topology.
• This finding provides key mechanistic insights into the regulation of membrane fusion.