Structural Basis of T Cell Toxicity Induced by Tigecycline Binding to the Mitochondrial Ribosome

Tetracyclines are essential bacterial protein synthesis inhibitors under continual development to combat antibiotic resistance yet suffer from unwanted side effects. Therefore, next-generation drugs should better discriminate between prokaryotic and eukaryotic ribosomes to ensure host cells remain unaffected by treatment. Mitoribosomes - responsible for generating oxidative phosphorylation (OXPHOS) subunits - share evolutionary features with the bacterial machinery and may suffer from cross-reactivity. T cells depend upon OXPHOS upregulation to power clonal expansion and establish immunity. To this end, we compared important bacterial ribosome-targeting antibiotics for their ability to induce immortalized and primary T cell death. Tetracyclines tested were cytotoxic and tigecycline (third generation) was identified as the most potent. In human T cells in vitro , 5-10 mM tigecycline inhibited mitochondrial but not cytosolic translation; mitochondrial complex I, III, and IV function, and naïve and memory T cell expansion. To determine the molecular basis of these effects, we isolated mitochondrial ribosomes from Jurkat T cells for cryo-EM analysis. We discovered tigecycline not only obstructs A-site tRNA binding to the small subunit, as it does in bacteria, but also attaches to the peptidyl transferase center of the mitoribosomal large subunit. Intriguingly, a third binding site for tigecycline on the large subunit—absent in bacterial structures—aligned with helices analogous to those in bacterial ribosomes, albeit lacking methylation in humans. The data show tigecycline compromises T cell survival and activation by binding to the mitoribosome, providing a molecular mechanism to explain part of the anti-inflammatory effects of this drug class. The identification of species-specific binding sites guides antibiotic and OXPHOS inhibitor design.