Bioprospecting of ornamental and weed plants for hydroxynitrile lyase activity and characterization of novel hydroxynitrile lyases (HNLs) of Euphorbia mili and Cascabela thevetia

Hydroxynitrile lyase enzymes are industrially important enzymes that are used to generate pure enantiomeric cyanohydrins in the fine chemical, pharmaceutical, and agrochemical industries. In nature, these enzymes are utilized by various organisms as a defence against herbivory or  microbial attacks. Upon mechanical damage, cyanoglycosides or cyanolipids stored in different cell compartments come into contact with hydroxynitrile lyase and cause the release of a cyanide group, which further causes poisoning of the attacking agent. Due to their capacity to generate biologically active, stereoselective products, hydroxynitrile lyases (HNLs) enzymes are in high demand across various sectors. This study used the Feigl Anger test-based high-throughput technique and the HNL activity assay to detect cyanogenic plants containing novel HNLs. Sixty-five species of ornamental and weed plants were screened for cyanogenic activity and their potential to degrade racemic mandelonitrile. Out of all plants, ten exhibited racemic mandelonitrile degrading potential. Maximum hydroxynitrile lyase activity was observed in Euphorbia mili and Cascabela thevetia, further characterized by reaction conditions.