Reconstitution of Mammalian Mitochondrial Translation System Capable of Long Polypeptide Synthesis

Mammalian mitochondria have their own dedicated protein synthesis system, which produces 13 essential subunits of the oxidative phosphorylation complexes. Here, we describe the in vitro reconstitution of the mammalian mitochondrial translation system, utilizing purified recombinant mitochondrial translation factors, 55S ribosomes from pig liver mitochondria, and a heterologous yeast tRNA mixture. The system is capable of translating leaderless mRNAs encoding model proteins, such as nanoluciferase with a molecular weight of 19 kDa, and is readily applicable for in vitro evaluations of mRNAs and nascent peptide chain sequences, as well as factors and small molecules that affect mitochondrial translation.

Cell-Based Fluorescent Screen Amenable to HTS to Identify Inhibitors of Bacterial Translation Initiation

A strategy that can be applied to the research of new molecules with antibacterial activity is to look for inhibitors of essential bacterial processes within large collections of chemically heterogeneous compounds. The implementation of this approach requires the development of assays aimed at the identification of molecules interfering with specific cell pathways that can also be used in high-throughput analysis of large chemical libraries. Here, we describe a fluorescence-based whole-cell assay in Escherichia coli devised to find inhibitors of the translation initiation pathway. Translation is a complex and essential mechanism. It involves numerous sub-steps performed by factors that are in many cases sufficiently dissimilar in bacterial and eukaryotic cells to be targetable with domain-specific drugs. As a matter of fact, translation has been proven as one of the few bacterial mechanisms pharmacologically tractable with specific antibiotics. The assay described in this updated chapter is tailored to the identification of molecules affecting the first stage of translation initiation, which is the most dissimilar step in bacteria versus mammals. The effect of the compounds under analysis is measured in living cells, thus allowing evaluation of their in vivo performance as inhibitors of translation initiation. Compared with other assays for antibacterials, the major advantages of this screen are its simplicity, high mechanism specificity, and amenability to scaling up to high-throughput analyses.

Protein synthesis in Mycobacterium tuberculosis as a potential target for therapeutic interventions

Mycobacterium tuberculosis (Mtb) causes one of humankind's deadliest diseases, tuberculosis. Mtb protein synthesis machinery possesses several unique species-specific features, including its ribosome that carries two mycobacterial specific ribosomal proteins, bL37 and bS22, and ribosomal RNA segments. Since the protein synthesis is a vital cellular process that occurs on the ribosome, a detailed knowledge of the structure and function of mycobacterial ribosomes is essential to understand the cell's proteome by translation regulation. Like in many bacterial species such as Bacillus subtilis and Streptomyces coelicolor, two distinct populations of ribosomes have been identified in Mtb. Under low-zinc conditions, Mtb ribosomal proteins S14, S18, L28, and L33 are replaced with their non-zinc binding paralogues. Depending upon the nature of physiological stress, species-specific modulation of translation by stress factors and toxins that interact with the ribosome have been reported. In addition, about one-fourth of messenger RNAs in mycobacteria have been reported to be leaderless, i.e., without 5' UTR regions. However, the mechanism by which they are recruited to the Mtb ribosome is not understood. In this review, we highlight the mycobacteria-specific features of the translation apparatus and propose exploiting these features to improve the efficacy and specificity of existing antibiotics used to treat tuberculosis.

Cell-Based Fluorescent Screen to Identify Inhibitors of Bacterial Translation Initiation

A strategy that can be applied to the research of new molecules with antibacterial activity is to look for inhibitors of essential bacterial processes within large collections of chemically heterogeneous compounds. The implementation of this approach requires the development of proper assays aimed at the identification of molecules interfering with specific cell pathways and potentially applicable to the high throughput analysis of large chemical library. Here, I describe a fluorescence-based whole-cell assay in Escherichia coli devised to find inhibitors of the translation initiation pathway. Translation is a complex and essential mechanism. It involves numerous sub-steps performed by factors that are in many cases sufficiently dissimilar in bacterial and eukaryotic cells to be targetable with domain-specific drugs. As a matter of fact, translation has been proven as one of the few bacterial mechanisms pharmacologically tractable with specific antibiotics. The assay described in this chapter is tailored to the identification of molecules affecting the first stage of translation initiation, which is the most dissimilar step in bacteria vs. mammals. The effect of the compounds under analysis is assayed in living cells, thus allowing evaluating their in vivo performance as inhibitors of translation initiation. Compared with other assays for antibacterials, the major advantages of this screen are its simplicity and high mechanism specificity.