Lay summary
Every cell in a living being is very sensitive to environmental supplies of nutrients as well as stress, and is thus obliged to keep a fine balance of all metabolites, biological macromolecules, and metal ions within its walls. To keep this delicate equilibrium in a narrow but life-supporting range, nature has developed several strategies to sense, take-up, use, and excrete or destroy molecules with specificity and efficiency. In the past five years, specific sequences in the 5'-untranslated regions (5'-UTR) of mRNA have been newly implicated in sensing different metabolites thereby regulating gene expression. The sensing of specific metal ions or metal ion complexes by nucleic acids poses an enormous challenge and must be dependent solely on basic coordination chemical principles.
In this project we concentrate on such so-called riboswitch sequences, which sense metal ions or complexes thereof, e.g. B12 derivatives: Adenosyl cobalamin belongs to the B12 family of coenzymes and is a crucial but highly light-sensitive cofactor for many radical reactions in the cell. This light sensitivity together with its complex chemical structure around the corrin ring and the organometallic Co2+/3+, makes this class of coenzymes challenging to investigate. In a first step we will synthesize light stable B12 derivatives. Having such derivatives at hand, we will then investigate the binding mode of these and naturally occurring B12 derivatives to the B12 responsive riboswitch sequence. This 202 nucleotide long RNA binds coenzyme B12 with high specificity and affinity undergoing an unknown structural change and thereby regulating the expression of B12 transport and/or B12 synthesizing enzymes.