Research Article: Crystal structures of Moorella thermoacetica cyanuric acid hydrolase reveal conformational flexibility and asymmetry important for catalysis

Date Published: June 10, 2019

Publisher: Public Library of Science

Author(s): Ke Shi, Seunghee Cho, Kelly G. Aukema, Thomas Lee, Asim K. Bera, Jennifer L. Seffernick, Lawrence P. Wackett, Hideki Aihara, Alessio Lodola.


An ancient enzyme family responsible for the catabolism of the prebiotic chemical cyanuric acid (1,3,5-triazine-2,4,6-triol) was recently discovered and is undergoing proliferation in the modern world due to industrial synthesis and dissemination of 1,3,5-triazine compounds. Cyanuric acid has a highly stabilized ring system such that bacteria require a unique enzyme with a novel fold and subtle active site construction to open the ring. Each cyanuric acid hydrolase monomer consists of three isostructural domains that coordinate and activate the three-fold symmetric substrate cyanuric acid for ring opening. We have now solved a series of X-ray structures of an engineered, thermostable cyanuric acid ring-opening enzyme at 1.51 ~ 2.25 Å resolution, including various complexes with the substrate, a tight-binding inhibitor, or an analog of the reaction intermediate. These structures reveal asymmetric interactions between the enzyme and bound ligands, a metal ion binding coupled to conformational changes and substrate binding important for enzyme stability, and distinct roles of the isostructural domains of the enzyme. The multiple conformations of the enzyme observed across a series of structures and corroborating biochemical data suggest importance of the structural dynamics in facilitating the substrate entry and the ring-opening reaction, catalyzed by a conserved Ser-Lys dyad.

Partial Text

Three hundred million pounds of cyanuric acid (1,3,5-triazine-2,4,6-triol, Fig 1A and 1C) are produced industrially due to its facile synthesis, high stability, and utility in the production of herbicides and disinfectants[1]. For disinfection, it is used directly to stabilize sodium hypochlorite or can be delivered as N,N,N-trichloroisocyanuric acid to provide both disinfection and stabilization in an aqueous environment. Nature predated anthropogenic cyanuric acid synthesis by billions of years with the compound being found in space[2] and s-triazines being formed in prebiotic chemistry experiments from simple precursors[3].