Crystal structure of type I 3-dehydroquinate dehydratase of Aquifex aeolicus suggests closing of active site flap is not essential for enzyme action

► Crystal structure of type I 3-dehydroquinate dehydratase from A. aeolicus was solved. ► The overall structure was similar to other type I 3-dehroquinate dehydratases. ► Flexible loop in the active site region was disordered and open in the ligand-bound structure. ► Closing of active site loop may not be essential for enzyme action. ► High intramolecular interactions and ion pairs impart thermostability to the enzyme.