Thiostrepton Biosynthesis: Prototype for a New Family of Bacteriocins

Abstract

Thiopeptide antibiotics are a group of highly modified peptide metabolites. The defining scaffold for the thiopeptides is a macrocycle containing a dehydropiperidine or pyridine ring, dehydrated amino acids, and multiple thiazole or oxazole rings. Some members of the thiopeptides, such as thiostrepton, also contain either a quinaldic acid or indolic acid substituent derived from tryptophan. Although the amino acid precursors of these metabolites are well-established, the biogenesis of these complex peptides has remained elusive. Whole-genome scanning of Streptomyces laurentii permitted identification of a thiostrepton prepeptide, TsrA, and involvement of TsrA in thiostrepton biosynthesis was confirmed by mutagenesis. A gene cluster responsible for thiostrepton biosynthesis is reported, and the encoded gene products are discussed. The disruption of a gene encoding an amidotransferase, tsrT, led to the loss of thiostrepton production and the detection of a new metabolite, contributing further support to the identification of the tsr cluster. The tsr locus also appears to possess the gene products needed to convert tryptophan to the quinaldic acid moiety, and an aminotransferase was found to catalyze an early step in this pathway. This work establishes that the thiopeptides are a type of bacteriocin, a family of genetically encoded antimicrobial peptides, and are subjected to extensive posttranslational modification during maturation of the prepeptide.

Clostridiolysin S, a Post-translationally Modified Biotoxin from Clostridium botulinum

“…In this regard, the chemistry described by these systems is very different. In clostriodiolysin S, an amide carbonyl undergoes activation, as is the case for microcin B17, patellamide, goadsporin, and the recently described thiopeptide family (13)(14)(15)(16)27). Because ClosA contains a C-terminal asparagine, in addition to several Ser, Thr, B, shown is the genetic complementation of Clos genes in GAS M1 Sag mutants.…”

“…ClosBCD resembles the McbBCD-modifying proteins found in the Escherichia coli microcin B17 system and the Prochloron didemni patDG genes of the patellamide biosynthetic gene cluster. This family of natural product toxins was recently shown by several groups to include the thiopeptides, which are nearly ubiquitous in soil-dwelling Bacillus and Streptomyces bacteria (12)(13)(14)(15)(16). In the microcin B17 system, McbB, -C, and -D were shown to be necessary and sufficient for the installation of heterocyclic moieties on C-terminal serine and cysteine residues of the McbA substrate.…”

Catalytic promiscuity in the biosynthesis of cyclic peptide secondary metabolites in planktonic marine cyanobacteria

“…Recent genomeenabled studies have shown that many classes of peptide natural products initially suspected to be of nonribosomal origin are in fact gene-encoded (e.g., refs. [2][3][4][5][6] and that structural motifs previously thought to be found only in nonribosomal secondary metabolites are also found in ribosomally synthesized compounds (7). Clearly, synthesis of secondary metabolites via the ribosome turns out to be much more widespread than originally anticipated.…”

In vitro activity of the nisin dehydratase NisB

“…The LanB dehydratases are 115-120 kDa proteins that do not share homology with the dehydratases from classes II-IV lanthipeptides or other proteins in the databases. Genes encoding homologous LanB-like enzymes are also present in the gene clusters of nonlantibiotic peptide natural products, such as the thiopeptides (16)(17)(18)(19) and goadsporin (20). These proteins are also believed to be dehydratases.…”