Reversible Redox-Responsive Peptide Condensates With RNA

While the amino acid cysteine is usually an "order promoting" amino acid, not normally found in disordered proteins which undergo phase separation, researchers have found cysteine-rich regions flanking low-complexity domains, imparting redox sensitivity to condensates both in vivo and in vitro. However, these examples of redox reversible condensates in vitro lose their reversibility when RNA (an integral component of biomolecular condensates) is added. Herein, we demonstrate a system where a cationic peptide containing a cysteine residue forms redox reversible condensates with RNA. Additionally, this peptide formed condensates with RNA preferentially over the DNA analogs of the sequence, demonstrating the importance of RNA in this system. Fluorescence recovery experiments determined that the condensates displayed similar viscoelastic properties after dissolution and reformation in this manner, and finally a control peptide lacking a cysteine did not form condensates under oxidizing conditions.