6.3.3.1 K27L obtained by site-directed mutagenesis and expression in Escherichia coli 6.3.3.1 K27Q obtained by site-directed mutagenesis and expression in Escherichia coli 6.3.3.1 K27R obtained by site-directed mutagenesis and expression in Escherichia coli 6.3.3.1 additional information double mutant R35C/E57G obtained by site-directed mutagenesis 6.3.3.1 additional information triple mutant R35C/E57G/R198W obtained by site-directed mutagenesis