6hag

Publication Abstract from PubMed

S-adenosylmethionine (SAM) is a central metabolite since it is used as a methyl group donor in many different biochemical reactions. Many bacteria control intracellular SAM concentrations using riboswitch-based mechanisms. A number of structurally different riboswitch families specifically bind to SAM and mainly regulate the transcription or the translation of SAM-biosynthetic enzymes. In addition, a highly specific riboswitch class recognizes S-adenosylhomocysteine (SAH)-the product of SAM-dependent methyl group transfer reactions-and regulates enzymes responsible for SAH hydrolysis. High-resolution structures are available for many of these riboswitch classes and illustrate how they discriminate between the two structurally similar ligands SAM and SAH. The so-called SAM/SAH riboswitch class binds both ligands with similar affinities and is structurally not yet characterized. Here, we present a high-resolution nuclear magnetic resonance structure of a member of the SAM/SAH-riboswitch class in complex with SAH. Ligand binding induces pseudoknot formation and sequestration of the ribosome binding site. Thus, the SAM/SAH-riboswitches are translational 'OFF'-switches. Our results establish a structural basis for the unusual bispecificity of this riboswitch class. In conjunction with genomic data our structure suggests that the SAM/SAH-riboswitches might be an evolutionary late invention and not a remnant of a primordial RNA-world as suggested for other riboswitches.

The structure of the SAM/SAH-binding riboswitch.,Weickhmann AK, Keller H, Wurm JP, Strebitzer E, Juen MA, Kremser J, Weinberg Z, Kreutz C, Duchardt-Ferner E, Wohnert J Nucleic Acids Res. 2018 Dec 27. pii: 5264287. doi: 10.1093/nar/gky1283. PMID:30590743^[1]

From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine.