Esther Braselmann, PhD, Clare Boothe Luce Assistant Professor, Georgetown

The Department of Chemistry Presents:  Esther Braselmann, PhD, Clare Boothe Luce Assistant Professor

Central roles for ribonucleic acids (RNAs) continue to be discovered across all domains of life. Subcellular RNA localizations in space and time are closely linked to their function, motivating the need to robustly visualize RNAs and their dynamics in live cells1. In contrast to the protein world, no genetically encoded fluorescent RNAs were found in nature, leading to intense tool development efforts. The Braselmann Lab is redesigning a bacterial RNA riboswitch as a fluorescence sensor, called Riboglow2. The riboswitch RNA can be genetically encoded as a tag to an RNA of interest. The natural riboswitch ligand Cobalamin (Cbl, vitamin B12) was designed into a small molecule probe that includes a synthetic fluorophore. Binding of the probe to the RNA tag with nM affinity induces a change in fluorescence intensity and fluorescence lifetime of the probe. They exploit fluorescence lifetime changes of the probe upon binding the RNA tag. They demonstrate that fluorescence lifetime imaging microscopy (FLIM) is an advantageous modality of Riboglow for RNA sensing in live cells. First, by demonstrating that cellular contrast is superior for lifetime imaging compared with intensity imaging. Second, the intensity independence of FLIM makes it unnecessary to multiplex the RNA tag to achieve intensity-contrast, a common strategy for traditional RNA fluorescent tags. Hence, one copy of the Riboglow tag (~100 nucleotides) for robust imaging with Riboglow-FLIM can be used. Finally, exploiting the phylogenetic diversity of the riboswitch sequence and showing that different RNA tag sequences bind the ligand while changing fluorescence lifetime to different extends. This feature leads to exploring Riboglow-FLIM as an RNA multiplexing sensor to detect different RNAs simultaneously in the same cell. Together, they demonstrate that FLIM is an advantageous approach for RNA sensing that addresses many current challenges in the field of RNA imaging tool development.

The Braselmann Lab investigates biochemistry in living cells, with the goal to understand how cellular perturbations alter biochemical processes in healthy and disease states. We are especially interested in probing dynamics of RNAs and proteins on a single cell level over time. How, when and where can we ‘see’ particular biomolecules within the cell, and what can we learn about the underlying biochemical process?

Dr. Braselman her degree in Biochemistry at Bielefeld University and her PhD at the University of Notre Dame.  She was a Postdoctoral Associate at the University of Colorado Boulder in the BioFrontiers Institute until she moved to Georgetown where she is a Clare Boothe Luce Assistant Professor in the Department of Chemistry.

1 Rathbun, C., et al. Cell Chem. Bio. 27(8) 891-903 (2020)
2 Braselmann, E. et al. Nat. Chem. Biol. 14, 964–971 (2018)
3 Sarfraz, N., et al. Nat. Comm., 14 (867), (2023)