title: Ligand-induced folding of the adenosine deaminase A-riboswitch and implications on riboswitch translational control.
abstract: By using a structure-based fluorescence spectroscopic approach, we have examined the folding of an adenine-responsive riboswitch that regulates translation initiation. We observed adaptive recognition of the ligand for the aptamer domain of adenosine deaminase (add) mRNA from Vibrio vulnificus, and revealed pronounced conformational changes even in the preorganized loop-loop region that is distant from the binding site. Importantly, the full-length riboswitch domain, which has a potential translational repressor stem is able to form a binary complex with adenine, and does not act as a folding trap to inhibit binding. The aptamer that is extended by the expression platform therefore remains fully responsive to its ligand; this is in contrast to the previously investigated pbuE A-riboswitch, which becomes trapped in a nonresponsive terminator fold. Consequently, the latter must employ complex response mechanisms, such as operating in kinetic-control mode or using transcriptional pausing, to provide time for the aptamer portion to fold and to bind. The different behavior of the riboswitches can be rationalized by their distinct sequence interface between the aptamer and expression platform. For the add A-riboswitch, our data suggest a thermodynamically driven response mechanism.
authors: Institute of Organic Chemistry, Center for Molecular Biosciences Innsbruck (CMBI), Leopold Franzens University, Innrain 52a, Innsbruck, Austria.
authors: Renate
authors: R
authors: Rieder
authors: Kathrin
authors: K
authors: Lang
authors: Dagmar
authors: D
authors: Graber
authors: Ronald
authors: R
authors: Micura
mesh_terms: D000243:Adenosine Deaminase / Q000096:biosynthesis / Q000235:genetics*; D052157:Aptamers, Nucleotide / Q000737:chemistry*; D001426:Bacterial Proteins / Q000096:biosynthesis / Q000235:genetics; D001483:Base Sequence; D001665:Binding Sites; D006860:Hydrogen Bonding; D008024:Ligands; D008958:Models, Molecular; D008969:Molecular Sequence Data; D009690:Nucleic Acid Conformation; D014176:Protein Biosynthesis / Q000235:genetics*; D017510:Protein Folding; D012333:RNA, Messenger / Q000737:chemistry*; D013050:Spectrometry, Fluorescence; D041261:Vibrio vulnificus / Q000201:enzymology
chemical_list: D052157:Aptamers, Nucleotide; D001426:Bacterial Proteins; D008024:Ligands; D012333:RNA, Messenger; D000243:Adenosine Deaminase