Biosynthesis and Ether‐Bridge Formation in Nargenicin Macrolides

Abstract

The nargenicin family of antibiotics are macrolides containing ar are ether-bridged cis-decalin motif.S everal of these compounds are highly active against multi-drug resistant organisms.D espite the identification of the first members of this family almost 40 years ago,t he genetic basis for the production of these molecules and the enzyme responsible for formation of the oxabridge,remain unknown. Here,the 85 kb nargenicin biosynthetic gene cluster was identified from ah uman pathogenic Nocardia arthritidis isolate and this locus is solely responsible for nargenicin production. Further investigation of this locus revealed ap utative iron-a-ketoglutarate-dependent dioxygenase,w hichw as found to be responsible for the formation of the ether bridge from the newly identified deoxygenated precursor,8 ,13-deoxynargenicin. Uncovering the nargenicin biosynthetic locus provides amolecular basis for the rational bioengineering of these interesting antibiotic macrolides. Figure 1. A) Comparison of HPLC traces of N. arthritidis AUSMDU00012717 extract with authenticn argenicin A1 standard at 265 nm. B) Structure of nargenicin A1.[*] Dr.

Global analysis of adenylate-forming enzymes reveals β-lactone biosynthesis pathway in pathogenic Nocardia

“…Despite this, only a small number of biosynthetic gene clusters in Nocardia have been experimentally-verified. Recently, the biosynthetic gene cluster for the nargenicin family of macrolide antibiotics was discovered in human pathogenic strains of Nocardia arthriditis (45). Khosla and colleagues also reported on a unique class of orphan polyketide synthases in the genomes of Nocardia isolates from human patients with nocardiosis (46).…”

The Nargenicin Family of Oxa‐Bridged Macrolide Antibiotics

“…The almost identical arrangement of domains and modules among the nar and stm PKSs, combined with the isolation of all nargenicin‐family antibiotics from Actinobacteria, strongly suggests a common evolutionary origin for these megasynthases, with the acquisition/loss of accessory genes within the corresponding gene clusters. This is further supported by the identification of orthologous nar and stm gene clusters in the genome sequences of other Nocardia and Streptomyces strains . The future genome sequencing of other nargenicin antibiotic producers, especially those that produce branimycin, lustromycin and luminamicin will provide further and much needed information on the evolution of this biosynthetic locus.…”

“…However, the isolation of both 11 and 1 from the same producing isolate, shows that all oxygenations are completed prior to the addition of the pyrrole‐2‐carboyl group . Furthermore, the isolation of 15 from a NarN knock‐out mutant suggests that ether bridge formation is actually the final biosynthetic step …”

“…The nar biosynthetic gene cluster encodes two putative P450 hydroxylases (NarG and NarM) and ap utative O-methyltransferase (NarK), which are most likely to hydroxylate the carbonsa tp ositions 2a nd 18, and then methylate the hydroxyl at C2. [42] Three orthologousp roteins are also encoded in the stm gene cluster and are the prime candidates to catalyse the equivalent reactions in the biosynthesis of 14. [18] Although the absolute configurationo f13 has not been confirmed, the presenceo fa na dditional O-methyl group at C3 suggestst hat an extra P450 hydroxylase and O-methyltransferase are likely encodedw ithin the genome of the producing Streptomyces strain.…”

Global analysis of adenylate-forming enzymes reveals β-lactone biosynthesis pathway in pathogenicNocardia

“…Despite this, only a small number of biosynthetic gene clusters in Nocardia have been experimentally-verified. Recently, the biosynthetic gene cluster for the nargenicin family of macrolide antibiotics was discovered in human pathogenic strains of Nocardia arthriditis (42). Khosla and colleagues also reported on a unique class of orphan polyketide synthases in the genomes of Nocardia isolates from human patients with nocardiosis (43).…”