An Electrostatic Re-Evaluation of Catalysis across Diverse Ribonuclease Classes

The catalytic efficiency of ribonucleases (RNases) is conventionally attributed to specific acid-base residues, metal cofactors, and conformational dynamics. Their apparent structural diversity may nevertheless reflect shared electrostatic principles that contribute to catalysis. In this review, we examine diverse RNase classes, including metal-independent, metal-dependent, and atypical toxin families, through the classic concept of electrostatic catalysis. Based on recent kinetic and thermodynamic data, such as heavy-atom kinetic isotope effects, substantial pKa shifts, and computational free energy profiles, we argue that RNase active sites can be understood as preorganized electrostatic environments that substantially contribute to catalysis. The protein scaffold rigidly positions a localized electric field to neutralize the accumulating negative charge of the pentacovalent phosphorane transition-state structure of the RNA substrate. Importantly, to avoid thermodynamic traps, natural RNases spatially segregate initial RNA recruitment from chemical catalysis. Extended cationic surfaces or accessory domains recruit the substrate by releasing its condensed counterions, driving an entropically favorable association. Decoupling long-range binding from transition-state stabilization allows these enzymes to optimize both affinity and turnover. These mechanisms may provide a conceptual framework for the rational design of artificial ribonucleases and compact, programmable biocatalysts for targeted RNA degradation.