Modulating condensate properties and catalytic activity with peptide sequence in coacervate dispersions

Condensation of biopolymers gives rise to distinct aqueous microenvironments that are proposed to help organise cellular as well as prebiotic (bio)chemistry. In addition to the spatial localization of reactants within these biomolecular condensates, reactions may also be modulated by the local physical properties of the condensate microenvironment. These properties in turn emerge from the sequence-encoded interactions of the molecular building blocks, which are often polypeptides and nucleic acids. To simultaneously explore both the potential influence of droplet physical properties on biochemical reactions in demixed systems as well as the control of those properties through polypeptide sequence, we use polyelectrolyte complex coacervate microdroplets prepared from an RNA enzyme and a small library of prebiotic peptide sequences as a minimal model system. Using quantitative phase microscopy and thermodynamic tie-line analysis, we measure the precise molecular composition of these condensates and find that that the phase behaviour is strongly influenced by peptide net charge and polar residue content. We show that small variations in peptide sequence can tune rates and yield of the ribozyme up to 15 times. Furthermore, we show that ribozyme rate constant is anti-correlated to the ribozyme concentration and correlated to the diffusion coefficient within the coacervates. Taken together, these results are a step towards linking polymer sequence to condensate properties and downstream catalytic function.