Unveiling the molecular basis of selective fluorination: computation-guided identification, characterization, and engineering of SAM-dependent fluorinases

S-adenosyl methionine (SAM)-dependent fluorinases have emerged as environmentally friendly alternatives for organofluorine synthesis. However, their use are limited by their rarity; only 16 fluorinases have so far been found in nature, and with limited SAM substrate specificities. Here we report two new fluorinases, FLASbac from Streptosporangiales bacterium and the N-terminal modified FLAAdig_Nter from Actinoplanes digitatis. Through molecular dynamics (MD) simulations, we proposed the critical roles played by the SAM-binding site and an identified ion-egress site (IES) in the fluorinase function such as fluoride ion preference. We confirmed these findings by testing respective mutants of these two new fluorinases, along with the known fluorinase from Streptomyces sp. MA37 (FLAMA37). Specifically, with these identified mutations, for the first time, we have managed to maintain fluorinase activity while also improving specificity towards fluoride ions over chloride ions. Overall, this research advances our fundamental understanding of enzymatic fluorination, paving the way for the rational design of fluorinases. These advancements will aid the pharmaceutical industry in developing fluorine-containing drugs and other fluorine-reliant biotechnologies.