The role of water in reactions catalysed by hydrolases under conditions of molecular crowding

Abstract

Under macromolecular crowding (MC) conditions such as cellular, extracellular, food and other environments of biotechnological interest, the thermodynamic activity of the diferent macromolecules present in the system is several orders of magnitude higher than in dilute solutions. In this state, the difusion rates are afected by the volume exclusion induced by the crowders. Immiscible liquid phases, which may arise in MC by liquid–liquid phase separation, may induce a dynamic confnement of reactants, products and/or enzymes, tuning reaction rates. In cellular environments and other crowding conditions, membranes and macromolecules provide, on the whole, large surfaces that can perturb the solvent, causing its immobilisation by adsorption in the short range and also afecting the solvent viscosity in the long range. The latter phenomenon can afect the conformation of a protein and/or the degree of association of its protomers and, consequently, its activity. Changes in the water structure can also alter the enzyme–substrate interaction, and, in the case of hydrolytic enzymes, where water is one of the substrates, it also afects the reaction mechanism. Here, we review the evidence for how macromolecular crowding afects the catalysis induced by hydrolytic enzymes, focusing on the structure and dynamics of water.