Deciphering the nucleotide driven kinetic and oligomeric dynamics in IMPDH regulation

Inosine monophosphate dehydrogenase (IMPDH) controls guanine nucleotide biosynthesis. Here, using biochemical and integrative structural biology approaches, we characterize the class II bacterial IMPDH from Burkholderia thailandensis. We demonstrate that MgGTP acts as a direct allosteric inhibitor independently of MgATP, promoting tetramer-to-octamer assembly via the Bateman domain. When both nucleotides are present, the enzyme exhibits a biphasic response: low MgGTP concentrations enhance activity, whereas higher concentrations restore inhibition. Structural analyses reveal distinct octameric conformations and capture a pre-catalytic Michaelis complex with substrates and effectors bound. These findings uncover a regulatory mechanism where the Bateman domain integrates opposing nucleotide signals to dynamically control guanine nucleotide biosynthesis, highlighting IMPDH as a potential antimicrobial target in pathogenic Burkholderia species.