Fig. 3. Interactions of antibiotics with the 50S ribosome. (A) The macrolide desosamine ring directly interacts with A2058 (N1) and forms water-bridged interactions with the indicated NPET residues (PDB: 6XHX). A2058 (N6) is the target site of macrolide-resistance 23S rRNA methyltransferases. For clarity, only residues of interest are shown; erythromycin is shown as yellow sticks. (B) Chemical structure of the 16-member macrolide tylosin. (C) Chemical structures of other PTC targeting antibiotics noted in the main text. (D) Chemical structure of streptogramin antibiotics. (E) Superposition of PTC binding antibiotics clindamycin (blue, PDB: 1JZX), chloramphenicol (yellow, PDB: 1K01), tiamulin (grey, PDB: 1XBP), linezolid (orange, PDB: 3CPW) and dalfopristin (light blue, PDB: 1SM1) from the respective ribosome-antibiotic cocrystal structures.