Crystallographic Analysis of Triclosan Bound to Enoyl Reductase Anna Roujeinikova 1 , Colin W. Levy 1 , Sia à n Rowsell 2 Svetlana Sedelnikova 1 , Patrick J. Baker 1 , Claire A. Minshull 2 Anil Mistry 2,6 , Jeremey G. Colls 2 , Roger Camble 2 , Antoine R. Stuitje 3 Antoni R. Slabas 4 , John B. Rafferty 1 , Richard A. Pauptit 2 Russell Viner 5 and David W. Rice 1 * 1 Krebs Institute for Biomolecular Research Department of Molecular Biology and Biotechnology, The University of Shef®eld Shef®eld S10 2TN, UK 2 AstraZeneca, Mereside, Alderley Park Maccles®eld Cheshire SK10 4TG, UK 3 Department of Genetics Institute of Molecular Biological Studies (IMBW), Vrije Universiteit, Biocenter Amsterdam, De Boelelaan 1087 1081 HV, Amsterdam The Netherlands 4 Department of Biological Sciences, The University of Durham, Durham DH1 3LE UK 5 Zeneca Agrochemicals, Jealott's Hill Research Station, Bracknell Berkshire RG12 6EY, UK 6 Parke Davis Pharmaceuticals Biomolecular Structure and Drug Design, 2800 Plymouth Road, Ann Arbor, MI 48105, USA Molecular genetic studies with strains of Escherichia coli resistant to triclo- san, an ingredient of many anti-bacterial household goods, have suggested that this compound works by acting as an inhibitor of enoyl reductase (ENR) and thereby blocking lipid biosynthesis. We present structural analyses correlated with inhibition data, on the complexes of E. coli and Brassica napus ENR with triclosan and NAD  which reveal how triclosan acts as a site-directed, picomolar inhibitor of the enzyme by mimicking its natural substrate. Elements of both the protein and the nucleotide cofactor play important roles in triclosan recognition, providing an explanation for the factors controlling its tight binding to the enzyme and for the emer- gence of triclosan resistance. # 1999 Academic Press Keywords: triclosan; inhibitor binding; enoyl reductase; crystal structure; resistance *Corresponding author Introduction The broad spectrum antimicrobial agent triclosan (5-chloro-2-(2,4-dichlorophenoxy) phenol) has long been used as a component of anti-microbial and anti-fungal wash products in homes and hospitals (Furia & Schenkel, 1968; Bhargava & Leonard, 1996). More recently, this compound has found E-mail address of the corresponding author: D.Rice@shef®eld.ac.uk Abbreviations used: ENR, enoyl reductase; ncs, non- crystallographic symmetry. Article No. jmbi.1999.3240 available online at http://www.idealibrary.com on J. Mol. Biol. (1999) 294, 527±535 0022-2836/99/470527±9 $30.00/0 # 1999 Academic Press