Formation of an aminovinyl-cysteine residue in thioviridamides occurs through a path independent of known lanthionine synthetase activity

Highlights

• Formation of an AviCys residue in thioviridamides relies on four dedicated proteins

• A lyase functionally associates with a phosphotransferase for Thr dehydration

• Kinase homolog TvaE plays a critical role in effective AviCys formation

• TvaE works with a LanD-like flavoprotein to form a minimum AviCys synthetase complex

Summary

2-Aminovinyl-cysteine (AviCys) is a thioether amino acid shared by a variety of ribosomally synthesized and posttranslationally modified peptides (RiPPs). Based on investigations into the biosynthesis of thioviridamide RiPPs in Streptomyces sp. NRRL S-87, we here report a path for the formation of this unusual thioether residue. This path relies on four dedicated proteins: phosphotransferase TvaC_S-87, Lyase TvaD_S-87, kinase homolog TvaE_S-87, and LanD-like flavoprotein TvaF_S-87. TvaE_S-87 plays a critical role in effective AviCys formation. During the posttranslational modifications of the precursor peptide, it works with TvaF_S-87 to form a minimum AviCys synthetase complex, which follows the combined activity of TvaCD_S-87 for Thr dehydration and catalyzes Cys oxidative decarboxylation and subsequent Michael addition of the resulting enethiol nucleophile onto the newly formed dehydroamino acid residue for cyclization. With TvaE_S-87, TvaF_S-87 activity for Cys processing can be coordinated with TvaCD_S-87 activity for minimizing competitive or unexpected spontaneous reactions and forming AviCys effectively.