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Antimicrobial Agents and Chemotherapy, January 2004, p. 30-40, Vol. 48, No. 1
0066-4804/04/$08.00+0     DOI: 10.1128/AAC.48.1.30-40.2004
Copyright © 2004, American Society for Microbiology. All Rights Reserved.

High-Throughput Screen for Inhibitors of Transglycosylase and/or Transpeptidase Activities of Escherichia coli Penicillin Binding Protein 1b

B. Chandrakala, Radha K. Shandil, Upasana Mehra, Sudha Ravishankar, Parvinder Kaur, Veeraraghavan Usha,⁰ Bina Joe, and Sunita M. deSousa^*

AstraZeneca India Pvt. Ltd., Bangalore 560 024, India

Received 7 May 2003/ Returned for modification 30 June 2003/ Accepted 23 September 2003

Penicillin binding protein (PBP) 1b of Escherichia coli has both transglycosylase and transpeptidase activities, which are attractive targets for the discovery of new antibacterial agents. A high-throughput assay that detects inhibitors of the PBPs was described previously, but it cannot distinguish them from inhibitors of the MraY, MurG, and lipid pyrophosphorylase. We report on a method that distinguishes inhibitors of both activities of the PBPs from those of the other three enzymes. Radioactive peptidoglycan was synthesized by using E. coli membranes. Following termination of the reaction the products were analyzed in three ways. Wheat germ agglutinin (WGA)-coated scintillation proximity assay (SPA) beads were added to one set, and the same beads together with a detergent were added to a second set. Type A polyethylenimine-coated WGA-coated SPA beads were added to a third set. By comparison of the results of assays run in parallel under the first two conditions, inhibitors of the transpeptidase and transglycosylase could be distinguished from inhibitors of the other enzymes, as the inhibitors of the other enzymes showed similar inhibitory concentrations (IC₅₀s) under both conditions but the inhibitors of the PBPs showed insignificant inhibition in the absence of detergent. Furthermore, comparison of the results of assays run under conditions two and three enabled the distinction of transpeptidase inhibitors. Penicillin and other ß-lactams showed insignificant inhibition with type A beads compared with that shown with WGA-coated SPA beads plus detergent. However, inhibitors of the other four enzymes (tunicamycin, nisin, bacitracin, and moenomycin) showed similar IC₅₀s under both conditions. We show that the main PBP being measured under these conditions is PBP 1b. This screen can be used to find novel transglycosylase or transpeptidase inhibitors.

Present address: Plexxikon, Berkeley, CA 94710.

Present address: 12/7 New Dhamu Nagar, Coimbatore 641 037, India.

Present address: Medical College of Ohio, Toledo, Ohio.

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