Empirical Valence Bond Simulations. Following our prior work, 18, 28 empirical valence bond simulations were performed on the GNCA4-WT, GNCA4-12, V4 and V4-4 variants, using the protocol and parameters presented in ref. . Protonation states of ionizable residues within the explicit simulation sphere, as well as histidine protonation patterns (both of which were validated by PROPKA 3.0 and visual inspection), can be found in Table . Note that we subtly updated our Morse and van der Waals parameters for the bonds changing during the Kemp elimination reaction in order to minimize system instabilities upon reaching the product state (otherwise in some replicas, too much force builds up on the proton being transferred leading to a system explosion). Sample input files, updated parameter files, starting structures and simulation snapshots, have all been submitted to Zenodo, DOI:10.5281/zenodo.12666978, along with the corresponding files describing our molecular dynamics simulations. In brief, each system was simulated in 30 replicas of 30 ns equilibration each followed by 10 ns of EVB simulations (200 ps window over 51 discrete EVB windows), leading to a cumulative 900 ns of EVB simulation time per system (including crystal and IN/OUT EVB calculations), and 3.6 µs of EVB simulation time across all systems studied in this work. All EVB simulations were performed using the Q6 simulation package, 82 the OPLS-AA force field, 83 the TIP3P water model, and the surface constrained all atom solvent (SCAAS) model 85 to describe solvent. Long range interactions were described using the local reaction field (LRF) approach. For further simulation details, see our prior work. Simulation Analysis. Unless specified otherwise in the text, all MD analysis was performed using the CPPTRAJ module 87 of AmberTools23. All analysis is based on extracting frames every 10 ps of each simulation trajectory and is presented (where relevant) as averages and standard deviations over 5 x 1 µs trajectories per system. In the case of donor-acceptor distance and donor-hydrogen-acceptor analysis, the "closest" keyword was used to ensure that distances Interaction Network Analysis. Key Interactions Finder (KIF) calculations were performed using mutual information analysis 91,92 to calculate the per residue interaction scores.