Client-scaffold interactions suppress aggregation of a client protein in model condensates

Area of Science:

• Biochemistry
• Molecular Biology
• Cell Biology

Background:

• Protein-protein interactions within cellular condensates can increase local concentrations, often promoting aberrant aggregation.
• However, the role of condensate environments in protecting client proteins from aggregation is less understood.

Purpose of the Study:

• To investigate how condensates formed by Cell Cycle Associated Protein 1 (CAPRIN1) influence the aggregation of its client, the Fused in Sarcoma (FUS) RNA Recognition Motif (RRM).
• To elucidate the molecular mechanisms by which CAPRIN1 condensates might suppress FUS RRM aggregation.

Main Methods:

• Nuclear Magnetic Resonance (NMR) spectroscopy was used to compare the FUS RRM domain in solution versus within CAPRIN1 condensates.
• Comparative NMR studies, including intermolecular NOE experiments, were performed on purified FUS RRM and FUS RRM:CAPRIN1 condensates.

Main Results:

• CAPRIN1 condensates suppressed FUS RRM aggregation, even at a twofold increased local concentration and with significant unfolding of the FUS RRM domain.
• CAPRIN1 was found to interact with multiple regions of the unfolded FUS RRM, including specific sequences like 287IFVQ290 and 351IDWFDG356.
• These heterotypic interactions between CAPRIN1 and FUS RRM outcompeted the homotypic interactions between FUS RRM protomers that drive aggregation.

Conclusions:

• Condensate scaffold molecules, like CAPRIN1, can protect client proteins from aggregation by shielding critical interprotomer interaction sites.
• This study provides a mechanism where specific molecular interactions within a condensate environment can prevent aberrant protein aggregation, contrasting with common observations.