Surface electrostatics dictate RNA-binding protein CAPRIN1 condensate concentration and hydrodynamic properties

Area of Science:

• Biochemistry and Molecular Biology
• Biophysics
• Cell Biology

Background:

• Biomolecular condensates are crucial for biological processes, concentrating molecules via balanced interactions.
• Charge-charge interactions, particularly involving intrinsically disordered regions, are key drivers of condensate formation.
• The RNA-binding protein CAPRIN1's disordered C-terminal region phase separates with ATP or high salt concentrations.

Purpose of the Study:

• To investigate the role of electrostatic potentials in CAPRIN1 phase separation induced by ATP and sodium chloride (NaCl).
• To compare residue-specific near-surface electrostatic potentials (ϕ_ENS) of CAPRIN1 under different phase separation conditions.
• To determine how variations in surface potential affect protein enrichment and condensate mechanical properties.

Main Methods:

• Utilized solution Nuclear Magnetic Resonance (NMR) spectroscopy to measure residue-specific near-surface electrostatic potentials (ϕ_ENS).
• Analyzed CAPRIN1's electrostatic properties along its NaCl-induced phase separation trajectory.
• Compared NMR data with potentials obtained for ATP-induced phase separation.

Main Results:

• Electrostatic shielding by both ATP and NaCl decreases ϕ_ENS values of CAPRIN1.
• Surface potentials of CAPRIN1 differ between ATP- and NaCl-induced condensates, depending on the concentration of the additive.
• Even minor differences in ϕ_ENS significantly alter protein enrichment and the mechanical characteristics of the condensed phase.

Conclusions:

• Electrostatic interactions and surface potential are critical determinants of biomolecular condensate formation and properties.
• Subtle modulation of surface electrostatics can lead to distinct condensate behaviors and biological outcomes.
• Findings provide insights into the regulation of biological processes through tunable condensate properties.