Mechanism of triclosan inhibition of bacterial fatty acid synthesis.
Triclosan is a broad-spectrum antibacterial agent that inhibits bacterial fatty acid synthesis at the enoyl-acyl carrier protein reductase (FabI) step. Resistance to triclosan in Escherichia coli is acquired through a missense mutation in the fabI gene that leads to the expression of FabI[G93V]. The specific activity and substrate affinities of FabI[G93V] are similar to FabI. Two different binding assays establish that triclosan dramatically increases the affinity of FabI for NAD+. In contrast, triclosan does not increase the binding of NAD+ to FabI[G93V]. The x-ray crystal structure of the FabI-NAD+-triclosan complex confirms that hydrogen bonds and hydrophobic interactions between triclosan and both the protein and the NAD+ cofactor contribute to the formation of a stable ternary complex, with the drug binding at the enoyl substrate site. These data show that the formation of a noncovalent "bi-substrate" complex accounts for the effectiveness of triclosan as a FabI inhibitor and illustrates that mutations in the FabI active site that interfere with the formation of a stable FabI-NAD+-triclosan ternary complex acquire resistance to the drug.
Heath
R J
RJ
Department of Biochemistry, St. Jude Children's Research Hospital, Memphis, Tennessee 38105, USA.
Rubin
J R
JR
Holland
D R
DR
Zhang
E
E
Snow
M E
ME
Rock
C O
CO
D050753:Enoyl-(Acyl-Carrier-Protein) Reductase (NADH); D005227:Fatty Acids / Q000037:antagonists & inhibitors* / Q000096:biosynthesis; D008958:Models, Molecular; D015394:Molecular Structure; D020125:Mutation, Missense; D009243:NAD / Q000378:metabolism; D010088:Oxidoreductases / Q000037:antagonists & inhibitors* / Q000235:genetics / Q000378:metabolism; D011485:Protein Binding; D014260:Triclosan / Q000737:chemistry / Q000378:metabolism / Q000494:pharmacology*
D005227:Fatty Acids; D009243:NAD; D014260:Triclosan; D010088:Oxidoreductases; D050753:Enoyl-(Acyl-Carrier-Protein) Reductase (NADH)