Mechanochemical Decoupling of ATP Hydrolysis and RNA Translocation in SARS-CoV-2 nsp13 by the L405D Mutation.

SARS-CoV-2 nonstructural protein 13 (nsp13) is a highly conserved helicase that couples ATP hydrolysis to RNA translocation through long-range allosteric communication between its ATPase and RNA-binding domains. In prior work, we identified L405 as a key regulator of interdomain motions and proposed that the L405D mutation would disrupt this coupling by perturbing conformational transitions required for translocation [J. Phys. Chem. B2024, v128, 492-503. ]. Subsequent experiments confirmed that L405D attenuates helicase activity and ATPase activity, implicating the potential formation of a new salt bridge, D405-R560, for both effects [ J. Biol. Chem.2026, v302, 111198.]. Here, we provide a data-driven explanation for both effects by combining Gaussian accelerated molecular dynamics (GaMD) simulations with Shape-GMM clustering and linear discriminant analysis. Whereas wild-type nsp13 exhibits both conformational selection and induction, L405D collapses the conformational landscape to operate predominantly through selection, with ATP-induced structural transitions observed in the wild-type ensemble no longer sampled by the mutant. This loss of induction likely impairs ATP turnover while simultaneously disrupting coordinated motif-RNA interactions required for inchworm translocation. These findings demonstrate how mutation-induced reshaping of conformational ensembles can modulate access to reaction-competent states, providing a general framework for understanding how targeted mutations disrupt catalytic function through allosteric ensemble remodeling in motor proteins.