Overall, we have demonstrated that important enzyme properties of HHDHs, such as activity, selectivity and stability, are influenced by the conserved residues threonine, phenylalanine/tyrosine and glycine of sequence motif 1 (T-X4-F/Y-X-G), which lines the nucleophile binding pocket of HHDHs. Despite the fact that those three residues appear to be highly conserved among naturally occurring HHDHs (please note that two highly homologous natural variants with sequence motif variation at the threonine position have been reported very recently ), we could show that especially the aromatic residue (phenylalanine/tyrosine) and the threonine position can be mutated to adjust enzyme properties, as exemplified for HheC. Only the conserved glycine residue of motif 1 proved quite invariable in both studied HHDHs as even the exchange by alanine resulted already in drastic activity losses toward most tested dehalogenation and epoxide ring opening reactions.