Mapping the per-residue surface electrostatic potential of CAPRIN1 along its phase-separation trajectory

Author:

Toyama Yuki123ORCID,Rangadurai Atul Kaushik1234,Forman-Kay Julie D.24ORCID,Kay Lewis E.1234

Affiliation:

1. Department of Molecular Genetics, University of Toronto, Toronto, ON M5S 1A8, Canada

2. Department of Biochemistry, University of Toronto, Toronto, ON M5S 1A8, Canada

3. Department of Chemistry, University of Toronto, Toronto, ON M5S 1A8, Canada

4. Program in Molecular Medicine, Hospital for Sick Children, Toronto, ON M5G 1X8, Canada

Abstract

Electrostatic interactions and charge balance are important for the formation of biomolecular condensates involving proteins and nucleic acids. However, a detailed, atomistic picture of the charge distribution around proteins during the phase-separation process is lacking. Here, we use solution NMR spectroscopy to measure residue-specific near-surface electrostatic potentials ( ϕ ENS ) of the positively charged carboxyl-terminal intrinsically disordered 103 residues of CAPRIN1, an RNA-binding protein localized to membraneless organelles playing an important role in messenger RNA (mRNA) storage and translation. Measured ϕ ENS values have been mapped along the adenosine triphosphate (ATP)–induced phase-separation trajectory. In the absence of ATP, ϕ ENS values for the mixed state of CAPRIN1 are positive and large and progressively decrease as ATP is added. This is coupled to increasing interchain interactions, particularly between aromatic-rich and arginine-rich regions of the protein. Upon phase separation, CAPRIN1 molecules in the condensed phase are neutral ( ϕ ENS 0 mV), with ∼five molecules of ATP associated with each CAPRIN1 chain. Increasing the ATP concentration further inverts the CAPRIN1 electrostatic potential, so that molecules become negatively charged, especially in aromatic-rich regions, leading to re-entrance into a mixed phase. Our results collectively show that a subtle balance between electrostatic repulsion and interchain attractive interactions regulates CAPRIN1 phase separation and provides insight into how nucleotides, such as ATP, can induce formation of and subsequently dissolve protein condensates.

Publisher

Proceedings of the National Academy of Sciences

Subject

Multidisciplinary

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