Poster Presentation 23rd International Society of Magnetic Resonance Conference 2023

Biosynthetic labeling of 13C-enriched 5-fluoro-tryptophan and characterization of conformational states of the enzyme fluoroacetate dehalogenase by 19F-13C two-dimensional NMR   (#232)

Motasem Suleiman 1 , Geordon Frere 1 , Lauren Tabunar 1 , Keith Taverner 1 , Oleksandr Voznyy 2 , Scott Prosser 1
  1. Chemical and Physical Sciences, University of Toronto Mississauga, Mississauga, Ontario, Canada
  2. Environmental Science & Chemistry, University of Toronto Scarborough, Scarborough, Ontario, Canada

Fluoroacetate dehalogenase (FAcD) is an extraordinary homodimeric enzyme which catalyzes the hydrolysis of a C-F bond, thereby neutralizing the toxic effects of fluoroacetate and generating glycolate, a halide ion and a proton as products.  FAcD acts exclusively through half-of-the-sites reactivity, utilizing an inter-protomer allosteric network to execute dynamics needed for catalysis. Given that this thermophilic enzyme possesses 9 distinct tryptophan residues within the hydrophobic interior of each protomer, 19F NMR of fluorotryptophan-enriched FAcD provides a convenient readout of local mobility, additional excited states, and allosteric inter-protomer dynamics. Resolution of all 9 tryptophans is impossible without resorting to two-dimensional (2D) NMR. Conveniently the scalar coupling between the 13C and 19F nuclei is nearly 300 Hz, permitting very efficient transfer of magnetization between the two nuclei and facilitating 19F,13C HSQC NMR. An efficient way of biosynthetically incorporating 13C-enriched 5-fluorotryptophan into a protein is to introduce 13C-enriched 5-fluoro-anthranilate as a metabolic precursor, prior to induction in E. coli, under glyphosate-induced auxotrophy. 5-fluoro-anthranilate is introduced at ~10 mg/liter with no scrambling and perfectly efficient incorporation into the protein. The resulting spectra of the apo protein reveal all 9 tryptophans and the titration of a substrate analog, bromoacetate, reveals a shift toward the Michaelis intermediate. The 2D-NMR spectrum provides an allosteric readout of all tryptophans in the protein, and their role in activation. Future NMR studies will focus on leveraging TROSY effects to improve on resolution and sensitivity.