Biochemical and structural characterization of a novel bacterial manganese‐dependent hydroxynitrile lyase

Hydroxynitrile lyases ( HNL s), which catalyse the decomposition of cyanohydrins, are found mainly in plants. In vitro , they are able to catalyse the synthesis of enantiopure cyanohydrins, which are versatile building blocks in the chemical industry. Recently, HNL s have also been discovered in bacteria. Here, we report on the detailed biochemical and structural characterization of a hydroxynitrile lyase from Granulicella tundricola ( G t HNL ), which was successfully heterologously expressed in Escherichia coli . The crystal structure was solved at a crystallographic resolution of 2.5 Å and exhibits a cupin fold. As G t HNL does not show any sequence or structural similarity to any other HNL and does not contain conserved motifs typical of HNL s, cupins represent a new class of HNL s. G t HNL is metal‐dependent, as confirmed by inductively coupled plasma/optical emission spectroscopy, and in the crystal structure, manganese is bound to three histidine and one glutamine residue. G t HNL displayed a specific activity of 1.74 U·mg −1 at p H 6 with ( R )‐mandelonitrile, and synthesized ( R )‐mandelonitrile with 90% enantiomeric excess at 80% conversion using 0.5  m benzaldehyde in a biphasic reaction system with methyl tertiary butyl ether.