pH-Tunable Material Properties of Glycine-Rich Condensates from Tick Bioadhesive

Liquid-liquid phase separation (LLPS) of biomolecules is crucial for maintaining the functional organization in biological systems. Intrinsically disordered proteins are particularly prone to LLPS and form condensates in response to various physicochemical triggers. This work studies the influence of pH on the LLPS behavior and material properties of condensates. A glycine-rich protein present in the saliva and the resulting bioadhesive of tick ectoparasites is selected for the study, given its ability to undergo LLPS. After confirming its disordered nature through spectroscopy, the effect on LLPS dynamics over a wide pH range of the full protein and its two halves is investigated. By combining fluorescence microscopy, droplet evaporation, and tensiometry assays, the findings reveal that pH-dependent changes in the protein hydrophobicity drive striking variations in the coacervation behavior, including the propensity to phase separate and the underlying microstructure dynamics. Importantly, pH dictates the viscosity of condensates and can confer amphiphilic character to the peptides, making them interfacially active. Lastly, pH-dependent curcumin encapsulation by condensates is demonstrated, exhibiting their potential as drug-delivery agents. Given the ubiquitous presence of disordered proteins in biology, this study provides valuable insights about the broad implications of the pH-dependent manifestation of the material properties of protein condensates.