Cis and trans interactions between atlastin molecules during membrane fusion

Area of Science:

• Cell Biology
• Membrane Trafficking
• Protein Biochemistry

Background:

• Atlastin (ATL) is a GTPase essential for endoplasmic reticulum (ER) membrane fusion and tubular network formation.
• The precise mechanism by which ATL mediates membrane fusion remains poorly understood.

Purpose of the Study:

• To elucidate the molecular mechanisms underlying atlastin-mediated ER membrane fusion.
• To investigate the role of GTP hydrolysis and ATL dimerization in the fusion process.

Main Methods:

• Studied ATL-mediated vesicle tethering and fusion.
• Utilized supported lipid bilayer experiments to analyze ATL dimerization on cis and trans membranes.
• Investigated the nucleotide-dependent behavior of ATL.

Main Results:

• ATL-mediated fusion is preceded by transient vesicle tethering, driven by ATL dimerization across opposing membranes.
• GTP hydrolysis, not just binding, is critical for strong ATL-mediated tethering, suggesting a role for the transition state.
• Multiple rounds of GTP hydrolysis are necessary for successful fusion due to futile tethering events.
• ATL molecules can dimerize within the same membrane (cis), and GTP hydrolysis is required to dissociate these cis dimers, releasing monomers for trans-dimerization.
• Successful fusion requires the cooperative action of multiple ATL molecules on each membrane.

Conclusions:

• A comprehensive model for atlastin-mediated membrane fusion is proposed, incorporating futile tethering and competition between cis and trans ATL interactions.
• GTP hydrolysis plays a dual role: driving trans-dimerization for tethering and dissociating cis-dimers to enable fusion.