Albany 2013: Book of Abstracts
June 11-15 2013
©Adenine Press (2012)
Cryo-EM Visualization of Mycobacterium 70S Ribosome Reveals Unique Structural Components at the Functional Sites
3D structures of prokaryotic and eukaryotic ribosomes by crystallography and electron microscopy have revealed that they share an evolutionarily conserved core (Schmeing & Ramakrishnan 2009) but each of the ribosomes contains its own set of specific proteins (or extensions of conserved proteins) and expansion segments of rRNAs (Melnikov et al 2012). How these differences correlate to function still remains largely unknown. A 3D cryo-EM map of the 70S ribosome from Mycobacterium smegmatis (Msm70S) unveiled striking new structural features (Shasmal & Sengupta 2012). The core of the Msm70S shows overall similarity with the core of the E coli 70S ribosome while containing additional mass in the periphery and solvent exposed sides. Some of the Mycobacterium ribosomal proteins are significantly bigger as compared the E. coli counter parts. The rRNAs also contains extra helices as also revealed by their secondary structures. Most of the additional density of the Msm70S can be largely attributed to the extra helices present in the rRNAs, and extra domains of homologous proteins.
One of the most notable features appears in the large subunit near L1 stalk as a structure forming a long helix with its upper end located in the vicinity of the mRNA exit channel (which we term the ‘steeple’).
We propose that the prominent helical structure in mycobacterium 23S rRNA participates in modulating different steps of translation, especially the E site tRNA exit mechanism and propagation of mRNA 5’ end.
S. Melnikov, S., Ben-Shem, A., Garreau de Loubresse, N., Jenner, L., Yusupova, G., Yusupov, M. (2012). One core, two shells: bacterial and eukaryotic ribosomes. Nat Struct Mol Biol. 19, 560-7.
M. Shasmal, M. and Sengupta, J. (2012). Structural Diversity in Bacterial Ribosomes: Mycobacterial 70S Ribosome Structure Reveals Novel Features (2012). PLoS One. 7(2), e31742.
Structural Biology & Bio-Informatics Division