Characterization of Histidine Functionalization and Its Timing in the Biosynthesis of Ribosomally Synthesized and Posttranslationally Modified Thioamitides.

Thioamitides are ribosomally synthesized and posttranslationally modified peptide (RiPP) natural products that hold great potential in anticancer drug development. Members in this RiPP family feature a thioamidated peptidyl chain conjugated with a macrocyclic ring system that contains two nonproteinogenic residues, 2- a mino vi nyl- cys teine (AviCys) and β- h ydroxy- N,N - d i m ethyl-l- his tidine (hdmHis). Focusing on the hdmHis residue that is unique to thioamitides, we report the enzymatic process for His functionalization and, more importantly, the timing of its related reactions with the other posttranslational modifications (PTMs) involved in thioamitide biosynthesis. His functionalization involves the activities of an S -adenosyl-l-methionine-dependent protein and a 2-oxoglutarate-Fe(II) monooxygenase for His bis- N -dimethylation and subsequent β-hydroxylation in a highly ordered manner. This process relies on the leader peptide sequence of the precursor peptide and on the establishment of the AviCys-containing, C-terminal macrocyclic ring system in particular. In contrast, prior peptide thioamidation is not required. Knowledge gained from the catalytic logic, specificity, and compatibility of His functionalization greatly furthers our understanding of the process through which nature develops thioamitides from a ribosomally synthesized peptide precursor.