Even though the actual effect of individual mutations is mainly enzyme dependent, mutagenesis of motif 1 residues can yield greatly improved enzyme variants such as HheC F12Y. This mutant features not only a higher thermal stability as reported earlier , but displays also much higher activity in the dehalogenation and epoxide ring opening of most substrates tested herein, as well as an impressive enantioselectivity improvement in the ring opening of epichlorohydrin (1), making this variant highly attractive for biocatalytic applications. Moreover, the detailed molecular insights into the activity improvement induced by mutation F12Y, which have been gained through QM and MD simulations in this study, will facilitate further protein engineering campaigns of HheC starting from mutant F12Y in the future.