Thiazolyl Peptide Antibiotic Biosynthesis: A Cascade of Post-translational Modifications on Ribosomal Nascent Proteins

Abstract

Antibiotics of the thiocillin, GE2270A, and thiostrepton class, which block steps in bacterial protein synthesis, contain a trithiazolyl (tetrahydro)pyridine core that provides the architectural constraints for high affinity binding to either the 50 S ribosomal subunit or elongation factor Tu. These mature antibiotic scaffolds arise from a cascade of post-translational modifications on 50 -60-residue prepeptide precursors that trim away the N-terminal leader sequences (ϳ40 residues) while the C-terminal 14 -18 residues are converted into the mature scaffold. In the producing microbes, the genes encoding the prepeptide open reading frames are flanked in biosynthetic clusters by genes encoding post-translational modification enzymes that carry out lantibiotic-type dehydrations of Ser and Thr residues to dehydroamino acid side chains, cyclodehydration and oxidation of cysteines to thiazoles, and condensation of two dehydroalanine residues en route to the (tetrahydro)pyridine core. The trithiazolyl pyridine framework thus arises from posttranslational modification of the peptide backbone of three Cys and two Ser residues of the prepeptide.

The posttranslational modification cascade to the thiopeptide berninamycin generates linear forms and altered macrocyclic scaffolds

“…With all other essential PTMs in place, the observation of the dehydrated as well as unprocessed residue 13 in the two compounds suggests that dehydration at this amino acid occurs just before pyridine formation, even though there are several serines and one threonine that are dehydrated both upstream and downstream of Ser 13 . This finding could be explained by the presence of two lantipeptide dehydratases in the berninamycin gene cluster, BerB and -C. One of the enzymes may carry out the phosphorylation/elimination sequence at several serines and Thr 4 , whereas the other dehydratase may subsequently act on the remaining unmodified residues. In one scenario, one dehydratase might process Ser 1,6,8,[10][11][14][15][16] and Thr 4 in an N-to-C direction, whereas the other may be dedicated to reaction at Ser 13 (SI Appendix, Fig.…”

“…heterologous expression | linear precursors | prepeptide gene replacement T he thiazolyl peptide (thiopeptide) antibiotics, first discovered in 1948, now number almost one hundred members and encompass a wide range of chemical diversity (1)(2)(3)(4)(5)(6)(7)(8). They can be classified into subgroups by several criteria, including the size of the macrocyclic ring(s), the oxidation state and substitution pattern of the central pyridine core, and also by the nature of the target in susceptible bacteria.…”

A Bright Future for Antibiotics?

“…Examples are those used recently to target Helix 69 (111), the first 16 residues of the proline-rich antimicrobial peptide mammalian Bac7 (112), the thiazolyl peptide antibiotics (113), and the small peptides that were shown to inhibit translation in prokaryotes (75,114).…”

At the Intersection of Chemistry, Biology, and Medicine

“…A subsequent study involved the family of almost 100 thiazole-containing peptide antibiotics of the thiocillin and thiostrepton class that target bacterial ribosomes. We and several other groups found the biosynthetic genes for such clusters and showed they are derived from posttranslational modification of nascent proteins (50). The trithiazolylpyridine core is a remarkable tetracyclic scaffold that anchors the macrocyclic peptidyl chains that make the inactivating contacts with the ribosome or the elongation factor EF-Tu.…”