Exploring Chloride Selectivity and Halogenase Regioselectivity of the SalL Enzyme through Quantum Mechanical/Molecular Mechanical Modeling

The catalytic mechanism of SalL chlorinase has been investigated by combining quantum mechanical/molecular mechanical (QM/MM) techniques and umbrella sampling simulations to compute free energy profiles. Our results shed light on the interesting fact that the substitution of chloride with fluorine in SalL chlorinase leads to a loss of halogenase activity. The potential of mean force based on DFTB3/MM analysis shows that fluorination corresponds to a barrier 13.5 kcal·mol–1 higher than chlorination. Additionally, our results present a molecular description of SalL acting as a chlorinase instead of a methyl-halide transferase.