Potential and capabilities of hydroxynitrile lyases as biocatalysts in the chemical industry.

The application of hydroxynitrile lyases (HNLs) as catalysts for the stereoselective condensation of HCN with carbonyl compounds has been reported as early as 1908. This enzymatic C-C bond coupling reaction furnishes enantiopure cyanohydrins which serve as versatile bifunctional building blocks for chemical synthesis. Screening of natural sources led to the discovery of both (R)- and (S)-selective HNLs, and several distinctly different classes of these enzymes with substantial differences concerning sequence, structure, and mechanism have been found. Especially during the last two centuries, HNLs have been developed into valuable biocatalysts, which can be produced in recombinant form by overexpression in microbial hosts, resulting in the implementation of industrial processes utilizing these enzymes. Recently, protein engineering in combination with in silico methods gave rise to the development of a tailor-made HNL for large-scale manufacturing of a specific target cyanohydrin.