Molecular Basis for the Selectivity of Antituberculosis Compounds Capreomycin and Viomycin

Abstract

Capreomycin and the structurally similar compound viomycin are cyclic peptide antibiotics which are particularly active against Mycobacterium tuberculosis, including multidrug resistant strains. Both antibiotics bind across the ribosomal interface involving 23S rRNA helix 69 (H69) and 16S rRNA helix 44 (h44). The binding site of tuberactinomycins in h44 partially overlaps with that of aminoglycosides, and they share with these drugs the side effect of irreversible hearing loss. Here we studied the drug target interaction on ribosomes modified by site-directed mutagenesis. We identified rRNA residues in h44 as the main determinants of phylogenetic selectivity, predict compensatory evolution to impact future resistance development, and propose mechanisms involved in tuberactinomycin ototoxicity, which may enable the development of improved, lesstoxic derivatives.Tuberculosis has been declared a global public health emergency by the World Health Organization. In 2000, worldwide there were about 9 million new cases and 2 million deaths due to tuberculosis (10). The emergence of multidrug-resistant (MDR) tuberculosis has further complicated treatment and control of the disease (1). Capreomycin and viomycin belong to the tuberactinomycins, an important class of antibiotics with activities against multidrug-resistant tuberculosis (12).Tuberactinomycins are cyclic peptide antibiotics (for chemical structures, see Fig. S1 in the supplemental material) which target bacterial protein synthesis by binding to the well-conserved intersubunit bridge B2a, formed by interaction between helix 69 (H69) of the 23S rRNA and helix 44 (h44) of the 16S rRNA ( Fig. 1A to C) (34). Inhibition of translocation during peptide elongation is the main mechanism of drug action mediating the compound's antibacterial activity (24,26). Mutational alterations of nucleotides in 23S or 16S rRNA affect drug binding (8,13,18,20,37). In addition, the loss of 2Ј-Omethylation of C1920 (rRNA nucleotides are numbered according to those for Escherichia coli throughout the paper) in H69 and that of C1409 in h44 by TlyA reduces susceptibility to capreomycin (17, 21). Interestingly, Thermus thermophilus TlyA modifies only C1920 in H69 of 23S rRNA, but not C1409 in h44 of 16S rRNA. Inactivation of tlyA in T. thermophilus does not affect its sensitivity to capreomycin (25), suggesting that modification of C1409 is the relevant determinant of increased drug susceptibility due to 2Ј-O-methylation.Much of the unwanted side effects of ribosomal antibiotics reflects limitations in selectivity (2, 3), as has been demonstrated for chloramphenicol and linezolid (23,38). Together with the structurally unrelated class of aminoglycoside antibiotics, the tuberactinomycins share ototoxicity (irreversible loss of hearing) as a common and unique side effect (7, 35). Tuberactinomycins affect bacterial protein synthesis apparently by stabilizing peptidyl-tRNA in the pretranslocation complex, preventing translocation of the ribosome along the mRNA (11,19,24,26). The recent crystal...

Evaluation of the AID TB Resistance Line Probe Assay for Rapid Detection of Genetic Alterations Associated with Drug Resistance in Mycobacterium tuberculosis Strains

“…For streptomycin resistance, mutations in rpsL (K43R, K88R, and K88Q) (22,23) and rrs (C513T, A514C, G515C, and C517T, corresponding to E. coli rrs positions 522, 523, 524, and 526, respectively) (18) were examined. Amikacin or capreomycin resistance was determined by screening the rrs gene for the mutations A1401G, C1402T, and G1484C/T (corresponding to E. coli rrs positions 1408, 1409, and 1491, respectively) (22,24,25). For fluoroquinolone resistance, GyrA amino acid mutations A90V, S91P, D94A, D94N, D94Y, and D94G were determined.…”

Molecular characterization of amikacin, kanamycin and capreomycin resistance in M/XDR-TB strains isolated in Thailand

“…Capreomycin binds across the 23S rRNA helix 69 and 16S rRNA helix 44 of the ribosome, resulting in inhibiting the protein synthesis [22,23]. Resistance to CAP has been reported to correlate with the gene encoding 2´-O-methyltransferase ( tlyA ) [24], although it is not a sensitive genetic marker for CAP resistance due to the infrequent finding [16].…”

Elements of ribosomal drug resistance and specificity

“…The binding of either aminoglycosides or tuberactinomycins to the ribosome increases the misincorporation of aminoacids in vitro , due to a mismatching between the tRNA anticodon and the mRNA codon in the A-site of the ribosome [11–14]. An amino-acylated tRNA progresses through multiple steps before its amino acid is incorporated into a nascent polypeptide chain.…”