The antibiotic resistance protein FusB rescues protein synthesis from inhibition by fusidic acid (FA), which locks elongation factor G (EF-G) to the ribosome after GTP hydrolysis. Here, we present time-resolved single-particle cryo-EM structures explaining the mechanism of FusB-mediated rescue. FusB binds to the FA-trapped EF-G on the ribosome, causing large-scale conformational changes of EF-G that break interactions with the ribosome, tRNA, and mRNA. This leads to dissociation of EF-G from the ribosome, followed by FA release. We also observe two independent binding sites of FusB on the classical-state ribosome, overlapping with the binding site of EF-G to each of the ribosomal subunits, yet not inhibiting tRNA delivery. The affinity of FusB to the ribosome and the concentration of FusB in S. aureus during FusB-mediated resistance support that direct binding of FusB to ribosomes could occur in the cell. Our results reveal an intricate resistance mechanism involving specific interactions of FusB with both EF-G and the ribosome, and a non-canonical release pathway of EF-G.
Organizational Affiliation:
Department of Cell and Molecular Biology, Uppsala University, BMC, Uppsala, Sweden.
Uppsala Antibiotic Center, Uppsala University, Uppsala, Sweden.
Proteomics Core Facility, Scilifelab and University of Gothenburg, Gothenburg, Sweden.
Department of Cell and Molecular Biology, Uppsala University, BMC, Uppsala, Sweden. maria.selmer@icm.uu.se.
Uppsala Antibiotic Center, Uppsala University, Uppsala, Sweden. maria.selmer@icm.uu.se.
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