Structural basis for the CsrA-dependent modulation of translation initiation by an ancient regulatory protein

• Published in: Proceedings of the National Academy of Sciences - PNAS Vol. 113; no. 36; pp. 10168 - 10173
• Main Authors: Altegoer, Florian, Rensing, Stefan A., Bange, Gert
• Format: Journal Article
• Language: English
• Published: United States National Academy of Sciences 06.09.2016
• Subjects: Allosteric Regulation; Amino Acid Motifs; Bacillus subtilis - classification; Bacillus subtilis - genetics; Bacillus subtilis - metabolism; Bacteria; Binding Sites; Biological Sciences; Carbon sequestration; Cloning, Molecular; Crystallography, X-Ray; Escherichia coli - genetics; Escherichia coli - metabolism; Escherichia coli Proteins - chemistry; Escherichia coli Proteins - genetics; Escherichia coli Proteins - metabolism; Flagella - chemistry; Flagella - metabolism; Flagella - ultrastructure; Flagellin - chemistry; Flagellin - genetics; Flagellin - metabolism; Gene Expression; Geobacillus - classification; Geobacillus - genetics; Geobacillus - metabolism; Homeostasis; Models, Molecular; Peptide Chain Initiation, Translational; Phylogenetics; Phylogeny; Protein Binding; Protein Conformation, alpha-Helical; Protein Conformation, beta-Strand; Protein Interaction Domains and Motifs; Protein Multimerization; Proteins; Recombinant Proteins - chemistry; Recombinant Proteins - genetics; Recombinant Proteins - metabolism; Repressor Proteins - chemistry; Repressor Proteins - genetics; Repressor Proteins - metabolism; Ribonucleic acid; RNA; RNA, Bacterial - chemistry; RNA, Bacterial - genetics; RNA, Bacterial - metabolism; RNA-Binding Proteins - chemistry; RNA-Binding Proteins - genetics; RNA-Binding Proteins - metabolism; Structural analysis; Structural Homology, Protein; translation; crystallography; FliW; flagellum; CsrA
• ISSN: 0027-8424; 1091-6490; 1091-6490
• DOI: 10.1073/pnas.1602425113

Regulation of translation is critical for maintaining cellular protein levels, and thus protein homeostasis. The conserved RNA-binding protein CsrA (also called RsmA; for carbon storage regulator and regulator of secondary metabolism, respectively; hereafter called CsrA) represents a well-characterized example of regulation at the level of translation initiation in bacteria. Binding of a CsrA homodimer to the 5′UTR of anmRNA occludes the Shine–Dalgarno sequence, blocking ribosome access for translation. Small noncoding RNAs (sRNAs) can competitively antagonize CsrA activity by a well-understood mechanism. However, the regulation of CsrA by the protein FliW is just emerging. FliW antagonizes the CsrA-dependent repression of translation of the flagellar filament protein, flagellin. Crystal structures of the FliW monomer reveal a novel, minimal β-barrel-like fold. Structural analysis of the CsrA/FliW heterotetramer shows that FliW interacts with a C-terminal extension of CsrA. In contrast to the competitive regulation of CsrA by sRNAs, FliW allosterically antagonizes CsrA in a noncompetitive manner by excluding the 5′UTR from the CsrA–RNA binding site. Our phylogenetic analysis shows that the FliW-mediated regulation of CsrA regulation is the ancestral state in flagellated bacteria. We thus demonstrate fundamental mechanistic differences in the regulation of CsrA by sRNA in comparison with an ancient regulatory protein.