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Structure of the Guanidine III Riboswitch.

ABSTRACT: Riboswitches are structural elements found in mRNA molecules that couple small-molecule binding to regulation of gene expression, usually by controlling transcription or translation. We have determined high-resolution crystal structures of the ykkC guanidine III riboswitch from Thermobifida fusca. The riboswitch forms a classic H-type pseudoknot that includes a triple helix that is continuous with a central core of conserved nucleotides. These form a left-handed helical ramp of inter-nucleotide interactions, generating the guanidinium cation binding site. The ligand is hydrogen bonded to the Hoogsteen edges of two guanine bases. The binding pocket has a side opening that can accommodate a small side chain, shown by structures with bound methylguanidine, aminoguanidine, ethylguanidine, and agmatine. Comparison of the new structure with those of the guanidine I and II riboswitches reveals that evolution generated three different structural solutions for guanidine binding and subsequent gene regulation, although with some common elements.

SUBMITTER: Huang L

PROVIDER: S-EPMC5696562 | biostudies-literature | 2017 Nov

REPOSITORIES: biostudies-literature

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Structure of the Guanidine III Riboswitch.

Huang Lin L Wang Jia J Wilson Timothy J TJ Lilley David M J DMJ

Cell chemical biology 20171005 11

Riboswitches are structural elements found in mRNA molecules that couple small-molecule binding to regulation of gene expression, usually by controlling transcription or translation. We have determined high-resolution crystal structures of the ykkC guanidine III riboswitch from Thermobifida fusca. The riboswitch forms a classic H-type pseudoknot that includes a triple helix that is continuous with a central core of conserved nucleotides. These form a left-handed helical ramp of inter-nucleotide ...[more]

PMID: 28988949

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Project description:Plant cell walls contain a renewable, nearly limitless supply of sugar that could be used to support microbial production of commodity chemicals and biofuels. Imidazolium ionic liquid (IIL) solvents are among the best reagents for gaining access to the sugars in this otherwise recalcitrant biomass. However, the sugars from IIL-treated biomass are inevitably contaminated with residual IILs that inhibit growth in bacteria and yeast, blocking biochemical production by these organisms. IIL toxicity is, therefore, a critical roadblock in many industrial biosynthetic pathways. Although several IIL-tolerant (IILT) bacterial and yeast isolates have been identified in nature, few genetic mechanisms have been identified. In this study, we identified two IILTBacillus isolates as well as a spontaneous IILTEscherichia coli lab strain that are tolerant to high levels of two widely used IILs. We demonstrate that all three IILT strains contain one or more pumps of the small multidrug resistance (SMR) family, and two of these strains contain mutations that affect an adjacent regulatory guanidine riboswitch. Furthermore, we show that the regulation of E. colisugE by the guanidine II riboswitch can be exploited to promote IIL tolerance by the simple addition of guanidine to the medium. Our results demonstrate the critical role that transporter genes play in IIL tolerance in their native bacterial hosts. The study presented here is another step in engineering IIL tolerance into industrial strains toward overcoming this key gap in biofuels and industrial biochemical production processes.IMPORTANCE This study identifies bacteria that are tolerant to ionic liquid solvents used in the production of biofuels and industrial biochemicals. For industrial microbiology, it is essential to find less-harmful reagents and microbes that are resistant to their cytotoxic effects. We identified a family of small multidrug resistance efflux transporters, which are responsible for the tolerance of these strains. We also found that this resistance can be caused by mutations in the sequences of guanidine-specific riboswitches that regulate these efflux pumps. Extending this knowledge, we demonstrated that guanidine itself can promote ionic liquid tolerance. Our findings will inform genetic engineering strategies that improve conversion of cellulosic sugars into biofuels and biochemicals in processes where low concentrations of ionic liquids surpass bacterial tolerance.

Dataset Information

Structure of the Guanidine III Riboswitch.

Publications

Structure of the Guanidine III Riboswitch.

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