Minisymposium Presentation

Phase-separated condensates play a pivotal role in organizing biomolecular interactions within cells. In the context of the RNA silencing pathway, crucial for gene expression regulation and defense against foreign nucleic acids in organisms like C. elegans, Mutator foci serve as perinuclear germ granules facilitating siRNA amplification. The scaffolding protein MUT-16 orchestrates the assembly of Mutator complexes within these foci, with the exoribonuclease MUT-7 and bridging protein MUT-8 being key components. Despite the known role of MUT-8 in facilitating MUT-7 recruitment, the mechanism of its binding to MUT-16 remains elusive. Through multi-scale molecular dynamics simulations and in vitro experiments, we elucidated the molecular underpinnings of MUT-16 phase separation and MUT-8 recruitment. Coarse-grained simulations revealed the phase separation propensities of MUT-16 disordered regions, validated by experiments. Additionally, aromatic amino acids, particularly Tyr and Phe, were identified as essential for MUT-16 phase separation. Atomistic simulations unveiled the crucial cation-π interactions between Tyr residues of MUT-8 and Arg/Lys residues of MUT-16, highlighting the superiority of Arg-Tyr interactions over Lys-Tyr interactions in MUT-8 recruitment, as corroborated by in vitro mutagenesis experiments. Our findings provide valuable insights into the intricate molecular mechanisms governing biomolecular recruitment within phase-separated condensates.