Inosine 5'-monophosphate dehydrogenase (IMPDH) is a^ ubiquitous enzyme that catalyzes the NAD+ -dependent oxidation of inosine 5'-monophosphate into xanthosine 5'-monophosphate. This enzyme is formed of two distinct domains, a core domain where the catalytic reaction occurs, and a less-conserved Bateman domain. Our previous studies gave rise to the classification of bacterial IMPDHs into two classes, according to their oligomeric and kinetic properties. MgATP is a common effector but leading to different effects when it binds within the Bateman domain: it is either an allosteric activator for class I IMPDHs or a modulator of the oligomeric state for class II IMPDHs.To get insight into the role of the Bateman domain in the dissimilar properties of the two classes, deleted variants of the Bateman domain and chimeras issued from the interchange of the Bateman domain between the three selected IMPDHs have been generated and characterized using an integrative structural biology approach. Biochemical, biophysical, structural and physiological studies of these variants unveil the Bateman domain as being the carrier of the molecular behaviors of both classes. This article is protected by