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Roles of elusive translational GTPases come to light and inform on the process of ribosome biogenesis in bacteria - PubMed

Review

. 2018 Feb;107(4):445-454.

doi: 10.1111/mmi.13895. Epub 2017 Dec 29.

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Review

Roles of elusive translational GTPases come to light and inform on the process of ribosome biogenesis in bacteria

Michelle R Gibbs et al. Mol Microbiol. 2018 Feb.

Abstract

Protein synthesis relies on several translational GTPases (trGTPases), related proteins that couple the hydrolysis of GTP to specific molecular events on the ribosome. Most bacterial trGTPases, including IF2, EF-Tu, EF-G and RF3, play well-known roles in translation. The cellular functions of LepA (also termed EF4) and BipA (also termed TypA), conversely, have remained enigmatic. Recent studies provide compelling in vivo evidence that LepA and BipA function in biogenesis of the 30S and 50S subunit respectively. These findings have important implications for ribosome biogenesis in bacteria. Because the GTPase activity of each of these proteins depends on interactions with both ribosomal subunits, some portion of 30S and 50S assembly must occur in the context of the 70S ribosome. In this review, we introduce the trGTPases of bacteria, describe the new functional data on LepA and BipA, and discuss the how these findings shape our current view of ribosome biogenesis in bacteria.

© 2017 John Wiley & Sons Ltd.

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Figures

Figure 1
Figure 1. Homologous proteins EF-G, LepA, and BipA bind the ribosome similarly

(A) Structures of EF-G, LepA, and BipA. Domains G (blue), II (green), III (yellow), and V (orange) are homologous among the factors. Unique domains include EF-G domain IV (pink), LepA C-terminal domain (red), and BipA C-terminal domain (raspberry). Images are based on PDB ID files 4V5F, 5J8B, and 4ZCI. (B) Structures of EF-G, LepA, and BipA bound to the 70S ribosome. 50S subunit, gray; 30S subunit, light teal; P-site tRNA; dark gray. Color coding of GTPase domains as in panel A. Images are based on PDB ID files 4V5F, 4W2E, and 5AA0.

Figure 2
Figure 2. Assembly maps

Protein binding during assembly of the small (A) or large (B) subunit is depicted schematically. Arrows indicate hierarchical dependencies and shaded regions indicate temporal stages. Schemes are based on (Chen and Williamson, 2013; Davis et al., 2016).

Figure 3
Figure 3. RsgA binds the 30S subunit in a way that occludes IF1, IF3, and initiator tRNA

Interface view of the 30S subunit bound by RsgA (A) or by IF1, IF3, fMet-tRNA, and mRNA (B), as determined by cryo-EM studies (Hussain et al., 2016; Lopez-Alonso et al., 2017). 16S rRNA, gray; r proteins, cyan; RsgA, blue; IF1, magenta; IF3, orange; mRNA, green; fMet-tRNA, black. Head and body regions of the subunit are labeled. Images are based on PDB ID files 5NO3 and 5LMV.

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