The ribosome: mechanisms of function, drug target and disease

The ribosome is the essential macromolecular complex of protein synthesis in all living cells. Ribosomes translate the genetic information encoded in messenger RNA (mRNA) into amino acid sequences. The decoding site of the small ribosomal subunit, the A-site, couples the mRNA codons with the corresponding anticodons of cognate transfer RNAs (tRNA), while the peptidyl transferase center (PTC) of the large ribosomal subunit is responsible for peptide bond formation between the incoming amino acids and the growing peptide chain.

Different steps in translation are targeted by anti-infective agents, including such diverse drugs as aminoglycosides, macrolides, spectinamides and tetracyclines. In spite of decades of use of ribosomal drugs we still do only in part understand the principles which impact on the specificity, selectivity and toxicity of these agents. A detailed understanding of the mechanisms involved in resistance towards drugs targeting protein synthesis has long been hampered by the lack of a suitable model organism, due to the fact that rrn resistance mutations in general are recessive and that bacteria harbour multiple rRNA operons in their chromosome. We have constructed a single rRNA allelic eubacterial model system for introduction of defined rRNA point mutations to investigate structure-function relationships of rRNAs at a molecular level.

Mutations in mitochondrial ribosomal nucleic acids have been associated with human disease. However, experimental investigations on rRNAs in higher eukaryotes are complicated by the presence of several hundred gene copies of chromosomal rrn genes encoding ribosomal RNA. The multiplicity of genes encoding cytosolic and mitochondrial rRNAs in higher eukaryotes combined with the peculiarities of mitochondrial genetics have frustrated any attempt of genetic manipulation. We have now developed a genetic system for modelling eukaryotic rRNA sequence and structure in functional bacterial ribosomes.

In the laboratory we use a variety of techniques including genetics, microbiology, biochemistry, cell biology, animal models, transcriptomics and metabolomics to study mechanisms of ribosome function. This is done with the view to understand ribosome- associated diseases, to assess the determinants of antibiotic selectivity and drug specificity, and to understand the mechanisms of drug-associated toxicity. In collaboration with ETH and WSU we have started a drug development program by combining molecular genetics with chemical synthesis, i.e., using genetic mutants to guide the synthesis of novel aminoglycoside compounds with the view to develop derivatives with altered drug-target interaction. More recently, we have developed a strong interest in studying the downstream effects of mistranslation in higher eukaryotes.