Characterization of a novel natural tetracenomycin reveals crucial role of 4-hydroxy group in ribosome binding

The aromatic polyketides tetracenomycins were recently found to be potent inhibitors of protein synthesis. Their binding site is located in a unique locus within the tunnel of the large ribosomal subunit. Here we report the isolation and structure elucidation of a novel natural tetracenomycin congener – O 4 –Me-tetracenomycin C ( O 4 –Me-TcmC). This compound is isomeric to tetracenomycin X (TcmX), however, in contrast to TcmX, O 4 –Me-TcmC, exhibited no antimicrobial activity and was unable to inhibit protein synthesis in vitro . Structural alignment of tetracenomycins to the binding locus from cryo-EM TcmX-70S ribosome data revealed the crucial role of the 4-hydroxyl group. These findings are important for further development of semi-synthetic tetracenomycins as potential antibacterials. • O 4 –Me-tetracenomycin C ( O 4 –Me-TcmC) is produced by strain Amycolatopsis A23. • O 4 –Me-TcmC is an isomer of tetracenomycin X (TcmX). • 4-Metylation leads to complete loss of activity and binding affinity. • Structural alignment with the ribosome corroborates the essential role of the 4-OH group.