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First published on July 27, 2006; DOI: 10.1124/mol.106.026567

0026-895X/06/7004-1271-1280$20.00
Mol Pharmacol 70:1271-1280, 2006

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On the Mechanism of Action of 9-O-Arylalkyloxime Derivatives of 6-O-Mycaminosyltylonolide, a New Class of 16-Membered Macrolide AntibioticsFormula

Panagiotis Karahalios, Dimitrios L. Kalpaxis, Hong Fu, Leonard Katz, Daniel N. Wilson, and George P. Dinos

Laboratory of Biochemistry, School of Medicine, University of Patras, Patras, Greece (P.K., D.L.K., G.P.D); Kosan Biosciences Inc., Hayward, California (H.F., L.K.); Max-Planck-Institute für Molekulare Genetik, AG Ribosomen, Berlin, Germany (D.N.W.)

New 16-membered 9-aryl-alkyl oxime derivatives of 5-O-mycaminosyl-tylonolid (OMT) have recently been prepared and were found to exhibit high activity against macrolide-resistant strains. In this study, we show that these compounds do not affect the binding of tRNAs to ribosomes in a cell-free system derived from Escherichia coli and that they cannot inhibit peptidyltransferase, peptidyl-tRNA translocation, or poly(U)-dependent poly(Phe) synthesis. However, they severely inhibit poly(A)-dependent poly(Lys) synthesis and compete with erythromycin or tylosin for binding to common or partially overlapping sites in the ribosome. According to footprinting analysis, the lactone ring of these compounds seems to occupy the classic binding site of macrolides that is located at the entrance of the exit tunnel, whereas the extending alkyl-aryl side chain seems to penetrate deeper in the tunnel, where it protects nucleoside A752 in domain II of 23S rRNA. In addition, this side chain causes an increased affinity for mutant ribosomes that may be responsible for their effectiveness against macrolide resistant strains. As revealed by detailed kinetic analysis, these compounds behave as slow-binding ligands interacting with functional ribosomal complexes through a one-step mechanism. This type of inhibitor has several attractive features and offers many chances in designing new potent drugs.

Received May 11, 2006; accepted July 27, 2006

Address correspondence to: George P. Dinos, Laboratory of Biochemistry, School of Medicine, University of Patras, 26500-Patras, Greece. E-mail: geodinos{at}med.upatras.gr






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