Phosphate closes the solution structure of the 5-enolpyruvylshikimate-3-phosphate synthase (EPSPS) from Mycobacterium tuberculosis.

The 5-enolpyruvylshikimate-3-phosphate synthase catalyses the sixth step of the shikimate pathway. This pathway is responsible for synthesis of aromatic compounds and is absent in mammals, a fact that make it a potential target for drugs against pathological diseases. Actuality, the 5-enolpyruvylshikimate-3-phosphate synthase is the target of the herbicide Round-up. Here, we report phosphate effects on the structure of the 5-enolpyruvylshikimate-3-phosphate synthase from Mycobacterium tuberculosis, the etiological agent of the tuberculosis which infects of about 9 million people annually. The 5-enolpyruvylshikimate-3-phosphate synthase is formed by two similar domains which close on each other after ligand binding, suggesting the occurrence of a large conformation changes. We monitored these conformational changes by small angle X-ray scattering and circular dichroism techniques. Small angle X-ray scattering shows that in the presence of phosphate ions the enzyme clearly presents a more compact structure. Thermal-induced unfolding experiments followed by circular dichroism suggest that phosphate shifted the unfolding curve to upper temperatures rigidifying the enzyme structure. Altogether, our data shows that phosphate ion is able to induce conformational changes on the M. tuberculosis 5-enolpyruvylshikimate-3-phosphate synthase leading it to a conformation resembling that of the closed state. Data from isothermal titration calorimetry corroborate to these conclusions. The results presented here are important in the enzyme-ligand interaction mechanism context, for determining the phosphate ion importance for other ligand interaction and consequently in a drug development context.