Vesicle Tethering on the Surface of Phase-Separated Active Zone Condensates

Area of Science:

• Neuroscience
• Cell Biology
• Biophysics

Background:

• Synaptic vesicle (SV) tethering to the active zone is crucial for synaptic strength.
• The molecular mechanisms underlying SV tethering remain largely unknown.

Purpose of the Study:

• To elucidate the molecular basis of synaptic vesicle tethering at the active zone.
• To investigate the role of protein-protein interactions and phase separation in synaptic structure formation.

Main Methods:

• Utilized in vitro reconstitution of presynaptic bouton-like structures.
• Employed phase separation principles to form liquid condensates of active zone proteins (RIM, RIM-BP, ELKS).
• Investigated interactions between small unilamellar vesicles (SUVs), SVs, and protein condensates.

Main Results:

• Discovered that SUVs and SVs from rat brains coat active zone protein condensates (RIM, RIM-BP, ELKS).
• Observed formation of two distinct SUV pools (reserve and tethered) through encapsulation by synapsin/SUV condensates.
• Demonstrated clustering of Ca2+ channels by SUV-coated RIM/RIM-BP condensates.
• Successfully reconstituted a presynaptic bouton-like structure mimicking SV tethering.

Conclusions:

• Membraneless protein condensates and membrane-bound organelles interact distinctly, providing a model for SV tethering.
• This mechanism has broad implications for vesicular transport, organelle biogenesis, and autophagy.