Structural Diversity in Bacterial Ribosomes: Mycobacterial 70S Ribosome Structure Reveals Novel Features

Abstract

Here we present analysis of a 3D cryo-EM map of the 70S ribosome from Mycobacterium smegmatis , a saprophytic cousin of the etiological agent of tuberculosis in humans, Mycobacterium tuberculosis . In comparison with the 3D structures of other prokaryotic ribosomes, the density map of the M. smegmatis 70S ribosome reveals unique structural features and their relative orientations in the ribosome. Dramatic changes in the periphery due to additional rRNA segments and extra domains of some of the peripheral ribosomal proteins like S3, S5, S16, L17, L25, are evident. One of the most notable features appears in the large subunit near L1 stalk as a long helical structure next to helix 54 of the 23S rRNA. The sharp upper end of this structure is located in the vicinity of the mRNA exit channel. Although the M. smegmatis 70S ribosome possesses conserved core structure of bacterial ribosome, the new structural features, unveiled in this study, demonstrates diversity in the 3D architecture of bacterial ribosomes. We postulate that the prominent helical structure related to the 23S rRNA actively participates in the mechanisms of translation in mycobacteria.

Structure of Ribosomal Silencing Factor Bound to Mycobacterium tuberculosis Ribosome

“…A wealth of structural and biochemical studies on the ribosome published over the last two decades have led to a deeper understanding of the mechanism of translation (Ban et al, 2000; Gao et al, 2009; Harms et al, 2001; Korostelev et al, 2006; Moore, 2012; Schuwirth et al, 2005; Selmer et al, 2006; Shasmal and Sengupta, 2012; Yusupov et al, 2001). Ribosome structures have provided molecular details for the machinery of translation as well as information on how drugs bind to the ribosome and interfere with protein synthesis (Wilson, 2014).…”

Specialization from synthesis: How ribosome diversity can customize protein function

“…The small subunit rRNA in T. cruzi has two large expansion segments of 147 and 504 nt that together form a massive 205 Å structural element, positioned so that it might play a role in recruiting the distinctive trans-spliced mRNAs to the ribosome [17]. Interestingly, the use of expanded rRNA is not confined to eukaryotes as cryo-electron microscopy revealed that Mycobacterium smegmatis has an expanded large subunit rRNA that forms a unique helical structure that juts out of the large subunit towards the mRNA exit channel [18]. In growing cells, the massive cellular demand on ribosome synthesis requires rRNA to be produced rapidly and at high levels [19].…”

34 Cyo-EM visualization ofMycobacterium70S ribosome reveals unique structural components at the function sites

“…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 Escherichia coli 70S ribosome while containing additional mass in the periphery and solvent exposed sides.…”