a, Superposition of the X-ray crystal structure of ribosome-bound lincosamide antibiotic clindamycin (2, blue, PDB entry 4V7V30) with the energy-minimized structure of OPP-1 (green). Note that in this configuration, the C7′-atom of OPP-1 contacts the lipophilic surface of the A-site cleft. b, The same structure, overlaid with the X-ray crystal structure of iboxamycin (IBX, yellow) bound to the bacterial ribosome.