Biomolecular Condensation of Trypsin Prevents Autolysis and Promotes Ca 2+ -Mediated Activation of Esterase Activity.

The presence of Ca 2+ ions is known to facilitate the activity of trypsin-like serine proteases via structural stabilization against thermal denaturation and autolysis. Herein, we report a new and hidden regulatory role of Ca 2+ in the catalytic pathways of trypsin and α-chymotrypsin under physiological conditions. We discovered that macromolecular crowding promotes spontaneous homotypic condensation of trypsin via liquid-liquid phase separation to yield membraneless condensates over a broad range of concentrations, pH, and temperature, which are stabilized by multivalent hydrophobic interactions. Interestingly, we found that Ca 2+ binding in the calcium binding loop reversibly regulates the condensation of trypsin and α-chymotrypsin. Spontaneous condensation effectively prevents autolysis of trypsin and preserves its native-like esterase activity for a prolonged period of time. It has also been found that phase-separated trypsin responds to Ca 2+ -dependent activation of its esterase activity even after 14 days of storage while free trypsin failed to do so. The present study highlights an important physiological aspect by which cells can spatiotemporally regulate the biocatalytic efficacy of trypsin-like serine proteases via Ca 2+ -signaling.