Capturing linear intermediates and C-terminal variants during maturation of the thiopeptide GE2270

Thiopeptides are ribosomally synthesized, posttranslationally modified peptides with potent activity against Gram-positives. However, only GE2270 has yielded semisynthetic derivatives under clinical investigations. The pbt gene cluster from the GE2270 producer Planobispora rosea was successfully expressed in the genetically tractable Nonomuraea ATCC39727. Gene deletions established that PbtO, PbtM1, PbtM2, PbtM3, and PbtM4 are involved in regiospecific hydroxylation and methylations of GE2270, leading to the generation of various derivatives with altered decorations. Further deletions established that PbtH and PbtG1 are involved in C-terminal amide and oxazoline formation, respectively. Surprisingly, preventing either step resulted in the accumulation of linear precursors in which the pyridine-generated macrocycle failed to form, and only one of the pyridine-forming serine residues had been dehydrated. Often, these linear precursors present a shortened C terminus but retain the full set of methylation and hydroxylation decorations.