Synapsin condensation is governed by sequence-encoded molecular grammars

Area of Science:

• Neuroscience
• Biochemistry
• Molecular Biology

Background:

• Biomolecular condensates at synapses regulate vesicle dynamics and neurotransmitter release.
• Intrinsically disordered regions (IDRs) of synaptic proteins drive condensate formation, clustering synaptic vesicles (SVs).

Purpose of the Study:

• To investigate conserved sequence patterns and compositional biases in SV protein IDRs.
• To dissect the role of specific features within the synapsin-1 C-terminal IDR in driving SV condensation.

Main Methods:

• Computational analysis of SV protein IDRs.
• Site-directed mutagenesis of synapsin-1 IDR features (polar/proline segregation, arginine vs. lysine preference).
• Co-expression studies with synaptophysin and assessment of condensate formation and pH gradients.

Main Results:

• Conserved non-random compositional biases and sequence patterns exist in SV protein IDRs.
• Scrambling polar/proline residues weakened condensate driving forces but not subsaturated clustering.
• Arginine to lysine substitution significantly impaired both condensation driving forces and clustering.
• Synapsin-1 condensation generates interphase pH gradients crucial for neurotransmitter loading.

Conclusions:

• Conserved IDR grammars in synapsin-1 are key drivers of synaptic vesicle condensation.
• Specific sequence features, particularly arginine preference, are essential for condensate stability and function.
• Synapsin-1 condensation-driven pH gradients impact vesicular ATPase activity and neurotransmitter uptake.