PMID: 28988949

Authors:

Huang L, Wang J, Wilson TJ, Lilley DMJ

Title:

Structure of the Guanidine III Riboswitch.

Journal:

Cell Chem Biol. 2017 Sep 28. pii: S2451-9456(17)30319-7. doi:, 10.1016/j.chembiol.2017.08.021.

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.