Regulation of the macrolide resistance ABC-F translation factor MsrD

Antibiotic resistance ABC-Fs (ARE ABC-Fs) are translation factors currently proliferating among human pathogens that provide resistance against clinically important ribosome-targeting antibiotics. Here, we combine genetic and structural approaches to determine the regulation of streptococcal ARE ABC-F gene msrD in response to macrolide exposure and also demonstrate that MsrD twin-ATPase sites work asymmetrically to mediate the dynamic of MsrD interaction with the ribosome. We show that cladinose-containing macrolides lead to insertion of MsrDL leader peptide into an undocumented conserved crevice of the ribosomal exit tunnel concomitantly with 23S rRNA rearrangements that prevent peptide bond formation and preclude accommodation of release factors. The stalled ribosome obstructs formation of a Rho-independent terminator which prevents msrD transcriptional attenuation. This stalled ribosome is rescued by MsrD, but not by MsrD mutants which do not provide antibiotic resistance, showing evidence of equivalence between MsrD function in antibiotic resistance and its action on this complex.