An L-threonine transaldolase is required for L-threo-β-hydroxy-α-amino acid assembly during obafluorin biosynthesis

Abstract

β-Lactone natural products occur infrequently in nature but possess a variety of potent and valuable biological activities. They are commonly derived from β-hydroxy-α-amino acids, which are themselves valuable chiral building blocks for chemical synthesis and precursors to numerous important medicines. However, despite a number of excellent synthetic methods for their asymmetric synthesis, few effective enzymatic tools exist for their preparation. Here we report cloning of the biosynthetic gene cluster for the β-lactone antibiotic obafluorin and delineate its biosynthetic pathway. We identify a nonribosomal peptide synthetase with an unusual domain architecture and an L-threonine:4-nitrophenylacetaldehyde transaldolase responsible for (2S,3R)-2-amino-3-hydroxy-4-(4-nitrophenyl)butanoate biosynthesis. Phylogenetic analysis sheds light on the evolutionary origin of this rare enzyme family and identifies further gene clusters encoding L-threonine transaldolases. We also present preliminary data suggesting that L-threonine transaldolases might be useful for the preparation of L-threo-β-hydroxy-α-amino acids.

An unusual metal-bound 4-fluorothreonine transaldolase from Streptomyces sp. MA37 catalyses promiscuous transaldol reactions

“…Naturally occurring β-hydroxy-α-amino acids (βH-AAs) are key residues in many bioactive metabolites, such as glycopeptide antibiotics (Williams 1984), cyclopeptides (Genet 1996) and β-lactone antibiotic obafluorin (Schaffer et al 2017;Scott et al 2017). Some of βH-AAs are also specialised metabolites with a range of antimicrobial and anticancer bioactivities.…”

“…These L-TTAs display narrow substrate specificity towards 6 and cannot utilise L-allo-threonine as substrates (Barnard-Britson et al 2012). This can be exemplified by two biochemically characterised L-TTAs: the L-threonine, uridine-5′-aldehyde transaldolase, LipK, in the biosynthesis of lipopeptidyl nucleoside natural product (Barnard-Britson et al 2012), and the Lthreonine, 4-nitrophenylacetaldehyde transaldolase, ObaG in the biosynthesis of obafluorin (Schaffer et al 2017;Scott et al 2017). FTase homologous genes have been mainly found in actinomycetes (Mcmurry and Chang 2017).…”

“…Some of βH-AAs also exist as specialised metabolites (Scott et al 2017). Among these βH-AAs, 4-fluorothreonine (4-FT) 1 is the only naturally occurring fluorinated amino acid.…”

Second messenger control of mRNA translation by dynamic ribosome modification

“…Purification vectors for rimA, rimB and rimK were as described in (30) using primers 7-12. P. fluorescens SBW25 site-specific mutants were constructed using a modification of the protocol described elsewhere (57). Up- and downstream flanking regions to the target modification site ( rimBK , hfq or rpsF ) were amplified using primers 19-25, 26-31 and 32-37 respectively.…”

Pan-genome analysis identifies intersecting roles for Pseudomonas specialized metabolites in potato pathogen inhibition

“…500 bp) to the target genes were amplified using primers listed in Table S2. PCR products in each case were ligated into pTS1 (110) between XhoI and BamHI. The resulting deletion vectors were transformed into the target strains by electroporation, and single crossovers selected on L + Tet and re-streaked to isolate single colonies.…”