Authors

J Masschelein¹; J Masschelein²; P K Sydor¹; P K Sydor²; D Griffiths¹; D Griffiths²; T R Valentic³; A Gallo¹; A Gallo²; C Jones⁴; L Song¹; L Song²; S C Tsai³; J R Lewandowski¹; J R Lewandowski²; E Mahenthiralingam⁴; G L Challis¹; G L Challis²;  ¹ Department of Chemistry, University of Warwick, CV4 7AL Coventry, UK ;  ² Department of Chemistry, University of Warwick, CV4 7AL Coventry, UK ;  ³ Departments of Molecular Biology and Biochemistry, Chemistry and Pharmaceutical Sciences, University of California, CA 92697-1450 Irvine, USA. ;  ⁴ Organisms and Environment Division, Cardiff School of Biosciences, Cardiff University, CF10 3AT Cardiff, Wales, UK

Discussion

Enacyloxin IIa is a polyketide antibiotic with potent activity against Gram-positive and Gram-negative bacteria that targets ribosomal elongation factor Tu.1-5 It has been identified as a metabolite of Burkholderia ambifaria AMMD and shown to have clinically-relevant activity against Acinetobacter baumannii, a problematic multidrug-resistant Gram-negative pathogen.6 Despite its promising biological activity, enacyloxin IIa is unlikely to find direct clinical application, given the densely-packed array of similar and potentially labile functional groups in the antibiotic. Enacyloxin biosynthesis has recently been mapped to an 80 kb gene cluster in the sequenced genome of B. ambifaria AMMD and a pathway for its biosynthesis has been proposed, involving assembly of the 27-carbon acyl chain by a modular polyketide synthase (PKS).6 The polyketide chain undergoes various modifications by on-/post-PKS tailoring enzymes, including halogenation, hydroxylation, carbamoylation and oxidation. Detailed structural and biochemical analyses have provided insights into an unusual mechanism of chain release in enacyloxin biosynthesis, showing that the enzymatic machinery is able to accommodate (1R, 3R, 4S)-3,4-dihydroxycyclohexane carboxylic acid (DHCCA) as well as a diverse set of analogues. Using a variety of rational engineering approaches, including mutasynthesis, gene deletion and gene replacement strategies, we are currently exploiting this biosynthetic knowledge for the production of novel analogues with improved pharmacological properties.
References: [1] Watanabe T, Izaki K, Takahashi H. New polyenic antibiotics active against gram-positive and gram-negative bacteria. I. Isolation and purification of antibiotics produced by Gluconobacter Sp. W-315. . J Antibiot (Tokyo) 1982, 35:1141-1147. [2] Watanabe T, Sugiyama T, Takahashi M, Shima J, Yamashita K, Izaki K, Furihata K, Seto H. New polyenic antibiotics active against gram-positive and gram-negative bacteria. IV. Structural elucidation of enacyloxin IIa. J Antibiot (Tokyo) 1992, 45:470-475. [3] Watanabe T, Okubo N, Suzuki T, Izaki K. New polyenic antibiotics active against gram-positive and gram-negative bacteria. VI. Non-lactonic polyene antibiotic, enacyloxin IIa, inhibits binding of aminoacyl-tRNA to A site of ribosomes. J Antibiot (Tokyo) 1992, 45:572-574. [4] Zuurmond AM, Olsthoorn-Tieleman LN, Martien de Graaf J, Parmeggiani A, Kraal B. Mutant EF-Tu species reveal novel features of the enacyloxin IIa inhibition mechanism on the ribosome. J Mol Biol 1999, 294:627-637. [5] Parmeggiani A, Krab IM, Watanabe T, Nielsen RC, Dahlberg C, Nyborg J, Nissen P. Enacyloxin IIa pinpoints a binding pocket of elongation factor Tu for development of novel antibiotics. J Biol Chem 2006, 281:2893-2900. [6] Mahenthiralingam E, Song L, Sass A, White J, Wilmot C, Marchbank A, Boaisha O, Paine J, Knight D, Challis GL. Enacyloxins are products of an unusual hybrid modular polyketide synthas