The invention relates to R-hydroxynitrillyases from the family of Rosaceae that are characterized by an improved substrate tolerance and increased stability. In the active center of the R-hydroxynitrillyases either a) an alanine group is substituted by glycine, valine, leucine, isoleucine, or phenylalanine or b) a phenylalanine group is substituted by alanine, glycine valine, leucine or isoleucine, or c) a leucine group is substituted by alanine, glycine, valine, isoleucine or phenylalanine, or d) an isoleucine group is substituted by alanine, glycine, valine, leucine or phenylalanine. The invention also relates to the use of these lyases in the production of enantiomer-pure R- or S-cyanohydrines.
1. An R-hydroxynitrile (R-HNL) lyase comprising the amino acid sequence of SEQ ID NO: 27.
2. A process for preparing enantiopure R-cyanohydrin comprising:
(a) contacting a substrate in the presence of a cyanide ion with the R-hydroxynitrile lyase of claim 1 in a reaction mixture, and
(b) recovering enantiopure R-cyanohydrin from the reaction mixture.
3. A process for preparing enantiopure R-cyanohydrins comprising contacting aliphatic, aromatic or heteroaromatic aldehydes or ketones in the presence of a cyanide ion with the R-hydroxynitrile lyase of claim 1 at a pH from 1.8 to 7.
4. The R-hydroxynitrile lyase of claim 1 which is obtained by expressing the nucleic acid encoding the R-hydroxvnitrile lyase of claim 1 in a microorganism.
5. The R-hydroxynitrile lyase of claim 4 , wherein said recombinant R-hydroxynitrile lyase is produced in a microorganism selected from the group consisting of Pichia pastoris, Saccharomyces cerevisiae, Escherichia coli, Bacillus subtilis, Kluyveromyces lactis, Aspergillus niger, Penicillium chrysogenum, Pichia methanolica, Pichia polymorpha, Pichia anomala , and Schizosaccharomyces pombe.
6. The R-hydroxynitrile lyase of claim 1 which is obtained by site-specific mutagenesis.
7. A process for preparing enantiopure R-cyanohydrin comprising contacting 2-chlorobenzaldehyde or 3-chlorobenzaldehyde in the presence of a cyanide ion with the R-hydroxynitrile lyase of claim 1 at a pH from 1.8 to 7.
8. The process according to claim 2 wherein said contacting occurs at a temperature from −5° C. to +45° C.
9. The process according to claim 7 wherein said contacting occurs at a temperature from −5° C. to +45° C.