Insights into the mechanism of type I dehydroquinate dehydratases from structures of reaction intermediates.

Abstract

The biosynthetic shikimate pathway consists of seven enzymes that catalyze sequential reactions to generate chorismate, a critical branch point in the synthesis of the aromatic amino acids. The third enzyme in the pathway, dehydroquinate dehydratase (DHQD), catalyzes the dehydration of 3-dehydroquinate to 3-dehydroshikimate. We present three crystal structures of the type I DHQD from the intestinal pathogens Clostridium difficile and Salmonella enterica. Structures of the enzyme with substrate and covalent pre- and post-dehydration reaction intermediates provide snapshots of successive steps along the type I DHQD-catalyzed reaction coordinate. These structures reveal that the position of the substrate within the active site does not appreciably change upon Schiff base formation. The intermediate state structures reveal a reaction state-dependent behavior of His-143 in which the residue adopts a conformation proximal to the site of catalytic dehydration only when the leaving group is present. We speculate that His-143 is likely to assume differing catalytic roles in each of its observed conformations. One conformation of His-143 positions the residue for the formation/hydrolysis of the covalent Schiff base intermediates, whereas the other conformation positions the residue for a role in the catalytic dehydration event. The fact that the shikimate pathway is absent from humans makes the enzymes of the pathway potential targets for the development of non-toxic antimicrobials. The structures and mechanistic insight presented here may inform the design of type I DHQD enzyme inhibitors.

• Authors: Samuel H Light, George Minasov, Ludmilla Shuvalova, Mark-Eugene Duban, Michael Caffrey, Wayne F Anderson, Arnon Lavie
• Journal: The Journal of biological chemistry (J Biol Chem) Vol. 286 Issue 5 Pg. 3531-9 (Feb 04 2011) ISSN: 1083-351X [Electronic] United States
• PMID: 21087925 (Publication Type: Journal Article, Research Support, N.I.H., Extramural, Research Support, Non-U.S. Gov't, Research Support, U.S. Gov't, Non-P.H.S.)

Chemical References

• 3-dehydroquinic acid
• Bacterial Proteins
• Schiff Bases
• Quinic Acid
• 3-dehydroshikimate
• Shikimic Acid
• Hydro-Lyases

Topics

• Bacterial Proteins
• Catalysis
• Catalytic Domain
• Clostridioides difficile (enzymology)
• Crystallography, X-Ray
• Hydro-Lyases (chemistry, metabolism)
• Protein Binding
• Protein Conformation
• Quinic Acid (analogs & derivatives, chemistry, metabolism)
• Salmonella enterica (enzymology)
• Schiff Bases
• Shikimic Acid (analogs & derivatives, metabolism)