The mfl-riboswitch regulates expression of ribonucleotide reductase subunit in Mesoplasma florum by binding to 2´-deoxyguanosine and thereby promoting transcription termination. We characterized the structure of the ligand-bound aptamer domain by NMR spectroscopy and compared the mfl-aptamer to the aptamer domain of the closely related purine-sensing riboswitches. We show that the mfl-aptamer accommodates the extra 2´-deoxyribose unit of the ligand by forming a more relaxed binding pocket than these found in the purine-sensing riboswitches. Tertiary structures of the xpt-aptamer bound to guanine and of the mfl-aptamer bound to 2´-deoxyguanosine exhibit very similar features, although the sequence of the mfl-aptamer contains several alterations compared to the purine-aptamer consensus sequence. These alterations include the truncation of a hairpin loop which is crucial for complex formation in all purine-sensing riboswitches characterized to date. We further defined structural features and ligand binding requirements of the free mfl-aptamer and found that the presence of Mg2+ is not essential for complex formation, but facilitates ligand binding by promoting pre-organization of key structural motifs in the free aptamer
Is data on this page outdated, violates copyrights or anything else? Report the problem now and we will take corresponding actions after reviewing your request.