4-chlorothreonine is present in nature as a constituent of antifungal lipodepsinonapeptides from Pseudomonas syringae1, of analogues of the anticancer agent actinomycin from Streptomyces fradie2 and as a free amino acid, produced by Streptomyces sp. OH-50933. Its formation by direct chlorination of threonine was inferred from radiolabelling experiments in the studies of syringomycin (SR)4 biosynthesis and demonstrated in enzymatic and structural studies of the halogenase SyrB25,6, which is a component of the multienzyme system involved in the biosynthesis of SR7. SyrB2 is a founding member of a new class of halogenases, belonging to the family of Fe(II) nonheme α-ketoglutarate dependent enzymes. In the present study we cloned and sequenced the biosynthetic cluster involved in the formation of 4-chlorothreonine in Streptomyces sp. OH-5093. The cluster is composed of the genes, thr1, thr2, thr3 and thr4 encoding a free-standing adenylation domain, a carrier protein, a Fe(II) nonheme halogenase and a thioesterase, respectively. Within the same transcriptional unit, two additional genes, orf1 and orf2, located between thr3 and thr4, were found. Orf1 shows homology with a family of Ala/Thr t-RNA synthetases editing domains. The sequence analysis of orf2 indicated similarity with the superfamily Drug Metabolite Transporters. The halogenase Thr3 can replace SyrB2 in the biosynthesis of SR. In fact, it can functionally complement the P. syringae strain BR135A1, inactivated in the gene syrB2 and unable to produce SR. Moreover, we report preliminary data on the structure-activity relationship of the new halogenase.
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|Titolo:||Molecular cloning of the biosynthetic cluster involved in the production of 4-chlorothreonine in Streptomyces sp. OH-5093: insight into the structure-activity relationship of a new nonheme Fe(II) halogenase|
|Data di pubblicazione:||2011|
|Appartiene alla tipologia:||04a Atto di comunicazione a congresso|