SNARE-mediated membrane fusion trajectories derived from force-clamp experiments

Area of Science:

• Biophysics
• Cell Biology
• Membrane Dynamics

Background:

• Membrane fusion is essential for cellular processes but faces significant energy barriers.
• These barriers include hydration shell removal, high curvature formation, and fusion pore expansion.

Purpose of the Study:

• To investigate the force-dependent kinetics of membrane fusion intermediates.
• To elucidate the primary free energy barriers governing SNARE-mediated bilayer merging.

Main Methods:

• Utilized atomic-force microscopy with membrane-coated silica spheres to measure force-dependent lifetimes of fusion intermediates.
• Employed force-clamp experiments and analyzed cantilever deflection time traces to identify membrane states.
• Compared wild-type SNAREs with SNARE mutants and non-SNARE conditions (PEG, calcium).

Main Results:

• Identified and characterized distinct intermediate states during SNARE-mediated fusion.
• Quantified the force-dependent lifetime distributions of these intermediates.
• Determined that the main free energy barrier is associated with overcoming hydration and lipid splaying.

Conclusions:

• The hydration barrier and lipid splaying are critical determinants of fusion pathway and rate.
• Wild-type SNAREs are essential for efficient bilayer merging, unlike mutants or non-SNARE conditions.
• This work provides a detailed mechanical map of the membrane fusion process.