The application of traditional NMR studies provides enormous amount of information on protein structure, but it is limited by the size of the protein. ¹⁹F-NMR is less explored in the field of biomolecular NMR although ¹⁹F-NMR can be used to study very large protein systems  and the fluorine chemical shift is very sensitive to the local environment  [1].  

DnaB helicase is a homohexameric protein with a molecular weight of 300kDa that helps in unwinding of the duplex DNA for replication. It had been reported DnaB helicase assumes different conformation under different biological conditions corresponding to C3 or C6 symmetry [2].  In this study we show how trifluoromethyl-phenylalanine (tfmF), fluorine containing analogue of phenylalanine was site specifically incorporated into E. coli DnaB helicase using cell-free protein synthesis to study its structure and was used to monitor structural changes of DnaB helicase in different conditions.