Hydroxynitrile lyases: Functions and properties

Abstract

Plant hydroxynitrile lyases (Hnl) have attracted the attention of bioorganic scientists for more than 90 years. However, the most important increase in knowledge of this class of enzymes has only arisen in the recent decade. The industrial application of these enzymes as biocatalysts for the synthesis of enantiomerically pure α‐cyanohydrins may be responsible for the growing interest in this area. The Hnls are involved in the catabolic degradation of cyanogenic glycosides, releasing HCN which serves as defense agent against herbivores and microbial attack, or as a nitrogen source. Hydroxynitrile lyases from various plant families appear to represent a new example of enzymes that originated from the convergent evolution of different precursor proteins. The enzymes have been classified into non‐FAD‐ and FAD‐containing proteins. FAD‐containing enzymes have been isolated exclusively from the Rosaceae, whereas the FAD‐independent Hnls, which are more heterogenous in structure, have been characterized from various plant families (Poaceae, Euphorbiaceae, Linaceae, Olacaceae. Filitaceae). The aim of this review is to present a general survey of the natural function and localization of this class of enzymes and a comprehensive summary of the biochemical and genetic data of the isolated proteins.

Three‐dimensional structures of enzyme‐substrate complexes of the hydroxynitrile lyase from hevea brasiliensis

“…1!. The release of HCN serves as a defense against herbivores and microbial attack for a variety of plants Conn, 1981;Hickel et al, 1996;Wajant & Effenberger, 1996! and is initiated by a b-glycosidases-mediated degradation of cyanoglycosides, forming a sugar and the a-hydroxynitrile~cyanohydrin!.…”

“…and is initiated by a b-glycosidases-mediated degradation of cyanoglycosides, forming a sugar and the a-hydroxynitrile~cyanohydrin!. In aqueous solution, cyanohydrin cleavage occurs spontaneously above pH 5, while the enzyme-catalyzed reaction also occurs at lower pH values~down to pH ; 3; Hickel et al, 1996!. …”

Identification and profiling of salinity stress-responsive proteins in Sorghum bicolor seedlings

“…Cyanogenic beta-glucosidases and hydroxynitrile lyases are both involved in the catabolism of cyanogenic glycosides [62], secondary metabolites, which play a role in the chemical defense system in plants and may also serve as nitrogen storage compounds [63,64]. During their catabolism, cyanogenic glycosides are hydrolysed by beta-glucosidases into alpha-hydroxynitrile, which are further broken down by alpha-hydroxynitrile lyases at low pH into keto compounds and hydrogen cyanide [62,65,66].…”

Observation of a Short, Strong Hydrogen Bond in the Active Site of Hydroxynitrile Lyase from Hevea brasiliensis Explains a Large pK Shift of the Catalytic Base Induced by the Reaction Intermediate

“…In aqueous solution, cyanohydrin cleavage occurs spontaneously above pH 5, whereas the enzyme reaction also occurs at lower pH values (down to ϳpH 3; Ref. 29). This is technologically exploited for the enantioselective synthesis of chiral cyanohydrins (31)(32)(33)(34)(35), making use of the reverse in vivo reaction.…”