|
Thiopeptide antibiotics are an important class of natural products which are rich in sulfur elements and their structures are highly midified. They show bioactivities against some bacterial strains resistant to most conventional treatments. Although they structures are different , especially construction of unusual amino acid residues is attracted by biologists and organic chemists in many years. In recent years, Research shows thiopeptide antibiotics are antibacterial peptides which are by the genome coding and generated by posttranslational modification after ribosome synthesis.Cyclothiazomycin (CLT) is a unique bridged macrocyclic thiopeptide, whose stereo structure was recently revealed as containing a dehydroserine, two dehydrothreonine residues, three thiazolines, three thiazoles, and a tri-substituted pyridine. Compared with common thiopeptides, it lacks the characteristic 2- and 3-azole substituent on the central pyridine domain, but instead, possesses an alanine-derived heterocyclic residue with (R)-configuration and a quaternary sulfide to exhibits two macro-cyclic peptide loops. In 2009, its gene cluster has been cloned, meanwhile, a profile of heterologous expression was successfully taken in S. lividans 1326, which is the first time for thiopeptides. Among them, the structural gene cltA produce prepeptide, by the posttranslational modification of protein in gene cluster, mature product is released to the extracellular.By site directed mutagenesis of Prepeptide and heterologous expression in S. lividans 1326, 14 mutants and 23 Cyclothiazomycin Variants are generated. Among them, the products of 6 mutants show bioactivities against Bipolaris maydis. We hope that through this method, not only can obtain more new thiopeptide antibiotics, but also can reveal the biosynthesis mechanism and bioactivity mechanism.
|