BACKGROUND: Cyanogenesis is a defense process of several thousand plant species. Hydroxynitrile lyase, a key enzyme of this process, cleaves a @entity66959 into @entity25231 and the corresponding @entity264 or @entity6178 . The reverse reaction constitutes an important tool in biocatalysis. Different classes of hydroxynitrile lyases have convergently evolved from @entity10697 -dependent oxidoreductases, alpha/beta hydrolases, and @entity167 dehydrogenases. The @entity10697 -dependent hydroxynitrile lyases ( @entity10697 -HNLs) carry a @entity1785 cofactor whose redox properties appear to be unimportant for catalysis. RESULTS: We have determined the crystal structure of a 61 kDa hydroxynitrile lyase isoenzyme from Prunus amygdalus (PaHNL1) to 1.5 A resolution. Clear electron density originating from four glycosylation sites could be observed. As concerns the overall protein fold including the @entity10697 cofactor, PaHNL1 belongs to the family of GMC oxidoreductases. The active site for the HNL reaction is probably at a very similar position as the active sites in homologous oxidases. CONCLUSIONS: There is strong evidence from the structure and the reaction product that @entity10697 -dependent @entity15542 lyases have evolved from an @entity23131 oxidizing precursor. Since key residues implicated in @entity6507 activity are also present in PaHNL1, it is not obvious why this enzyme shows no oxidase activity. Similarly, features proposed to be relevant for @entity15542 lyase activity in other hydroxynitrile lyases, i.e., a general base and a positive charge to stabilize the @entity3789 , are not obviously present in the putative active site of PaHNL1. Therefore, the reason for its HNL activity is far from being well understood at this point.

The hydroxynitrile lyase from almond: a lyase that looks like an XXXX .

@entity6507 :: ('8630', 'Gene') :: ['oxidoreductase'] @entity1785 :: ('MESH:C024132', 'Chemical') :: ['flavin'] @entity167 :: ('CHEBI:16236', 'Chemical') :: ['alcohol'] @entity23131 :: ('CHEBI:33853', 'Chemical') :: ['aryl alcohol'] @entity15542 :: ('CHEBI:24730', 'Chemical') :: ['hydroxynitrile', 'hydroxy-nitrile'] @entity3789 :: ('CHEBI:17514', 'Chemical') :: ['cyanide'] @entity10697 :: ('MESH:D005182', 'Chemical') :: ['FAD'] @entity6178 :: ('CHEBI:17087', 'Chemical') :: ['ketone'] @entity66959 :: ('MESH:C430593', 'Chemical') :: ['cyanohydrin'] @entity25231 :: ('MESH:D006856', 'Chemical') :: ['hydrocyanic acid'] @entity264 :: ('CHEBI:17478', 'Chemical') :: ['aldehyde']
@entity6507 :: (8630,Gene) :: ['oxidoreductase']
