Cryo-EM structure of the Mycobacterium smegmatis ribosome
Date of Issue2018-12-31
School of Biological Sciences
Ribosomes are the universal protein synthesis machineries in all living cells. These macromolecular structures can range from 2.5 (prokaryotes) to 4.2 MDa (eukaryotes) in size, undergo various different and precise movements to synthesis the nascent polypeptide chain. Ribosomes in the cells can exist in various functional states. Thus, to understand the process of translation completely, we must learn about these functional states as well. Although, many X-ray and high-resolution structures are available for ribosomes from different bacteria, a high-resolution structure of ribosome from Mycobacteria was lacking at the time this dissertation work started. Using cryo-electron microscopy and single-particle reconstruction, I have determined the structure of Mycobacterium smegmatis ribosome at its P/P state, characterized by the tRNA bound at the P-site to the resolution of 3.4 Å. The high-resolution structure has presented various insights about the species-specific rRNA and r-protein extensions. Along with the P/P state, two different functional states of M. smegmatis, the hibernating state (at 4.1 Å) and trans-translating state (12.5 Å) of 70S ribosomes were also investigated in this work. A possible theory for mycobacterial ribosome resuscitation from inactive ribosomal state is also discussed. The comparison of the three functional states of the mycobacterial ribosome will help in understanding the structure, function, and evolution of Mycobacteria. These studies will also help to understand the translation process in mycobacteria which could aid in discovery of novel targets against the pathogenic mycobacterial strains, a step towards the cure for Tuberculosis.