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Resistance to tetracycline (Tc), an inhibitor of protein synthesis, decreases its effectiveness for the treatment of bacterial infections. Tc resistance (TcR) can be mediated by the ribosomal protection protein, Tet(O), which was first reported in Campylobacter jejuni, a cause of bacterial diarrhea worldwide. Tet(O) confers TcR by mediating Tc release from 70S ribosomes, thus restoring protein synthesis. Tet(O) is widely distributed in a variety of bacterial genera, restraining the clinical use of Tc. This thesis is the first investigation into the role of the conserved set of amino acid residues, YSPVST, occupying positions 507-512 at the tip of domain IV of Tet(O). Impaired Tc release from 70S ribosomes observed with Tet(O)mutants lacking one or more of these conserved residues suggests residues at positions 509-512 play a role in Tet(O)-mediated TcR. This study provides insight into the molecular mechanism of TcR, which is essential for the development of novel therapeutics.

Widespread tetracycline resistance (TcR) has limited the clinical use of Tc for the treatment of bacterial infections. Tet(O) protein is present in many bacteria and is the major transmissible TcR determinant in Campylobacter jejuni, a common cause of acute bacterial diarrhea worldwide. Tet(O) protects ribosomes against the inhibition of protein synthesis by Tc. Tet(O) binds to the ribosome at a similar site as EF-G, a structural homologue of Tet(O) with GTPase activity that is required for protein elongation. EF-G interfered with the kinetics of Tet(O)-mediated Tc release suggesting that EF-G competes with Tet(O) for ribosome binding. Indirect assessment of EF-G and Tet(O) binding to 70S ribosomes by GTP hydrolysis was unable to clearly demonstrate competition for binding. This thesis contributed to the further understanding of the kinetics of Tc release by Tet(O), and may facilitate the development of novel strategies to overcome Tet(O)-mediated TcR in bacteria which cause human infections.

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