Allosteric network rewiring governs enzyme functional duality via a distal switch

How specialist enzymes reconcile the fundamental trade-off between catalytic fidelity and functional promiscuity within a conserved active site is a central paradox in enzymology. Using a representative Type II meso -DAPDH enzyme from Symbiobacterium thermophilum (StDAPDH) as our model system, we identify the distal residue M176 as a switch whose substitutions decouple the enzyme’s amination and deamination activities. We find that substitutions at this site are associated with substrate-dependent reorganization of the enzyme’s intra-subunit contact-correlation network. These network changes are accompanied by distinct substrate-dissociation free-energy profiles and catalytic outcomes, including activity retention, inhibition, and functional decoupling. Combined simulations and mutational analyses support the functional importance of specific residues associated with functional decoupling, while distinguishing recurring network-level features from putative residue-level routes. Together, these results provide an ensemble-based view of functional duality in Type II meso -DAPDH and suggest that distal network modulation may aid the engineering of substrate-dependent enzyme activities.