Synapsin Condensation is Governed by Sequence-Encoded Molecular Grammars

Area of Science:

• Neuroscience
• Biochemistry
• Cell Biology

Background:

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

Purpose of the Study:

• To investigate the role of conserved sequence features within the C-terminal IDR of synapsin-1 in driving SV condensation.
• To determine how specific sequence patterns, such as polar/proline residue segregation and arginine/lysine preference, affect condensate formation and function.

Main Methods:

• Computational analysis of SV protein IDRs for conserved patterns.
• In vitro experiments manipulating synapsin-1 IDR features (residue scrambling, substitutions).
• Cell-based co-expression assays to assess synapsin-1 function and condensate formation.

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 robust condensation and cellular function.
• Synapsin-1 condensation has emergent properties, including pH gradient formation, impacting synaptic vesicle function.