Rewiring V-type and K-type enzyme allostery through subunit interface mutations

Allosteric regulation in the heterodimeric enzyme IGPS depends on long-range communication between the effector-binding HisF subunit and the catalytic HisH subunit. This signaling occurs through a densely packed interdomain interface enriched in conserved noncovalent contacts. Here, we use targeted interface mutations to determine how specific interfacial contacts tune the structural and dynamic features that govern allosteric control. The hK181A variant, which disrupts a critical salt bridge with fD98, converts IGPS into a constitutively more active enzyme, increasing basal glutaminase activity and substrate affinity. By contrast, hR18A, which disrupts a secondary salt bridge with fE71, weakens effector-induced activation, revealing functional asymmetry among interfacial interactions. NMR chemical shift perturbation and CPMG relaxation dispersion experiments show that hK181A remodels millisecond-timescale dynamics throughout HisF, consistent with molecular dynamics simulations indicating enhanced sampling of catalytically competent conformations. Network traffic analysis of correlated communication pathways, combined with energetic analysis, further shows that enthalpic and entropic contributions are redistributed to rewire long-range allosteric signaling. Together, these results identify specific interfacial residues as molecular gates that shape the conformational ensemble accessible to IGPS and show how interface reengineering can be used to rationally reprogram allosteric output.