The magnitude of the allosteric conformational transition of aspartate transcarbamylase is altered by mutations.

Global conformational transitions are of central functional importance for many enzymes and binding proteins. It is not known, however, how much variability can exist in such structural-functional linkages. We have characterized the global magnitude of the T to R conformational transition of Escherichia coli aspartate transcarbamylase (ATCase) by measuring (1) hydration changes using osmotic stress and (2) hydrodynamic changes using high-precision analytical gel chromatography. We find that specific mutations can alter the structural magnitude of the enzyme's conformational transition without abolishing allostery, suggesting that some degree of plasticity exists in the conformational component of allostery.