Rachel A Powers | PubMed Health

PubMed2006

Structure determination and analysis of acyl-CoA oxidase (ACX1) from tomato.

The flavoenzyme acyl-CoA oxidase (ACX) catalyzes the first committed step in beta-oxidation and is required for the biosynthesis of jasmonic acid, a signaling molecule involved in plant defense. Recently, a mutant in tomato was identified that is deficient in jasmonic acid production and compromised in its wound response. This results from a single point mutation in acx1, which causes the conserved residue Thr138 to be substituted by isoleucine. To understand the structural basis for this mutation, the crystal structure of LeACX1 was determined to 2.74 Angstrom resolution by molecular replacement. Unexpectedly, an unusual packing arrangement was observed in which three monomers of LeACX1 are present in the asymmetric unit. Although the tertiary structure of LeACX1 is essentially similar to the previously determined structures of ACX enzymes, the packing within the unit cells is distinctly different.

Acyl-CoA Oxidase↗

PubMed2002

Structure-based approach for binding site identification on AmpC beta-lactamase.

Beta-lactamases are the most widespread resistance mechanism to beta-lactam antibiotics and are an increasing menace to public health. Several beta-lactamase structures have been determined, making this enzyme an attractive target for structure-based drug design. To facilitate inhibitor design for the class C beta-lactamase AmpC, binding site "hot spots" on the enzyme were identified using experimental and computational approaches. Experimentally, X-ray crystal structures of AmpC in complexes with four boronic acid inhibitors and a higher resolution (1.72 A) native apo structure were determined. Along with previously determined structures of AmpC in complexes with five other boronic acid inhibitors and four beta-lactams, consensus binding sites were identified. Computationally, the programs GRID, MCSS, and X-SITE were used to predict potential binding site hot spots on AmpC. Several consensus binding sites were identified from the crystal structures. An amide recognition site was identified by the interaction between the carbonyl oxygen in the R1 side chain of beta-lactams and the atom Ndelta2 of the conserved Asn152. Surprisingly, this site also recognizes the aryl rings of arylboronic acids, appearing to form quadrupole-dipole interactions with Asn152. The highly conserved "oxyanion" hole defines a site that recognizes both carbonyl and hydroxyl groups. A hydroxyl binding site was identified by the O2 hydroxyl in the boronic acids, which hydrogen bonds with Tyr150 and a conserved water. A hydrophobic site is formed by Leu119 and Leu293. A carboxylate binding site was identified by the ubiquitous C3(4) carboxylate of the beta-lactams, which interacts with Asn346 and Arg349. Four water sites were identified by ordered waters observed in most of the structures; these waters form extensive hydrogen-bonding networks with AmpC and occasionally the ligand. Predictions by the computational programs showed some correlation with the experimentally observed binding sites. Several sites were not predicted, but novel binding sites were suggested. Taken together, a map of binding site hot spots found on AmpC, along with information on the functionality recognized at each site, was constructed. This map may be useful for structure-based inhibitor design against AmpC.

Anti-Bacterial Agents↗

PubMed2002

Structure-based discovery of a novel, noncovalent inhibitor of AmpC beta-lactamase.

beta-lactamases are the most widespread resistance mechanisms to beta-lactam antibiotics, and there is a pressing need for novel, non-beta-lactam drugs. A database of over 200,000 compounds was docked to the active site of AmpC beta-lactamase to identify potential inhibitors. Fifty-six compounds were tested, and three had K(i) values of 650 microM or better. The best of these, 3-[(4-chloroanilino)sulfonyl]thiophene-2-carboxylic acid, was a competitive noncovalent inhibitor (K(i) = 26 microM), which also reversed resistance to beta-lactams in bacteria expressing AmpC. The structure of AmpC in complex with this compound was determined by X-ray crystallography to 1.94 A and reveals that the inhibitor interacts with key active-site residues in sites targeted in the docking calculation. Indeed, the experimentally determined conformation of the inhibitor closely resembles the prediction. The structure of the enzyme-inhibitor complex presents an opportunity to improve binding affinity in a novel series of inhibitors discovered by structure-based methods.

Ampicillin↗