Conformational Transitions in Yeast Chorismate Mutase Important for Allosteric Regulation as Identified by Nuclear Magnetic Resonance Spectroscopy

[Display omitted] •Yeast chorismate mutase (ScCM) was proposed to follow concerted MWC-type allostery.•ScCM does not fluctuate between T and R states in absence of allosteric effectors.•Allosteric inhibitor, Tyr, represses millisecond enzyme motions.•Allosteric activator, Trp, enhances millisecond enzyme motions.•This complex dynamic behavior is inconsistent with two-state concerted MWC model. Proteins fluctuate between different conformations in solution, and these conformational fluctuations can be important for protein function and allosteric regulation. The chorismate mutase from Saccharomyces cerevisiae (ScCM), a key enzyme in the biosynthesis of aromatic amino acids, is allosterically activated and inhibited by tryptophan and tyrosine, respectively. It was initially proposed that in the absence of effector, ScCM fluctuates between activated R and inhibited T conformations according to the Monod-Wyman-Changeux (MWC) model, although a more complex regulation pattern was later suggested by mutagenesis and kinetic data. Here we used NMR relaxation dispersion experiments to understand the conformational fluctuations on the microsecond-to-millisecond timescale that occur in ScCM. In the absence of allosteric effectors, ScCM did not exclusively exchange between T and R conformations, suggesting that the two-state MWC model is insufficient to explain conformational dynamics. Addition of tyrosine led to the quenching of much of the motion on this timescale, while new motions were identified in the presence of tryptophan. These new motions are consistent with conformational fluctuations into an alternative conformation that may be important for enzyme activity.