Surface Charge Can Modulate Phase Separation of Multidomain Proteins.

Area of Science:

• Biochemistry
• Molecular Biology
• Biophysics

Background:

• Biomolecular condensates form via phase separation, driven by multivalent protein interactions.
• The physical properties of folded domains influencing phase separation are not well understood.

Purpose of the Study:

• To investigate how domain surface charge affects multivalency-driven phase separation using a model system.
• To explore the role of histidine protonation in modulating phase separation.

Main Methods:

• Utilized a model system comprising small ubiquitin modifier (SUMO) and SUMO interaction motif (SIM) peptides.
• Manipulated pH to alter histidine protonation states and observed effects on polySUMO and polySIM phase separation.
• Employed histidine mutations to assess their impact on protein solubility and phase separation.
• Used atomistic modeling to quantitatively explain observed weak interactions.

Main Results:

• Phase separation of polySUMO and polySIM was sensitive to pH changes, linked to SUMO surface histidine protonation.
• Histidine mutations mimicked pH effects, altering SUMO solubility and phase separation in parallel.
• Atomistic modeling successfully explained the weak interactions governing phase separation.

Conclusions:

• Surface charge is a critical factor in tuning the phase separation of multivalent proteins.
• This finding suggests mechanisms for biological control, evolutionary adaptation, and therapeutic intervention in phase separation processes.