Binding of [acetyl-14C] Trichodermin to the Peptidyl Transferase Centre of Eukaryotic Ribosomes

Abstract

The antibiotic trichodermin, an inhibitor of the peptidyl transferase centre of eukaryotic ribosomes, was synthesized radioactively labeled. [acetyl-14C]Trichodermin (15.4 mCi/mmol) was obtained. [acetyl-14C]Trichodermin binds to ribosomes from yeast with a dissociation constant of 1.8 μM and to ribosomes of human tonsils with a dissociation constant of 0.67 μM but it does not bind to ribosomes of Escherichia coli. Similarly, the antibiotic binds to 60-S subunits derived from yeast ribosomes with a dissociation constant of 1.4 μM. A single-site interaction was observed in all cases. Trichodermin and anisomycin compete for binding to the peptidyl transferase centre. Although the activity of this centre is much affected by ionic conditions, the specific site of trichodermin interaction appears to be less sensitive since changes in ionic conditions, pH and ethanol concentration hardly modify the extent of antibiotic binding. Trichodermin binding to eukaryotic ribosomes is inhibited not only by anisomycin, but also by tenuazonic acid and a number of sesquiterpene antibiotics of the trichodermin group (tricho-dermol, trichothecin, fusarenon X and verrucarin A).