6 structures(e.g. : 6COC, 6COD, 6COE... more)(less)6COC: Structure of the hydroxynitrile lyase from Arabidopsis thaliana AtHNL enantioselectivity mutant At-A9-H7 Apo, Y13C,Y121L,P126F,L128W,C131T,F179L,A209I with benzaldehyde, 6COD: Structure of the hydroxynitrile lyase from Arabidopsis thaliana AtHNL enantioselectivity mutant At-A9-H7 Apo, Y13C,Y121L,P126F,L128W,C131T,F179L,A209I with benzaldehyde, 6COE: Structure of the hydroxynitrile lyase from Arabidopsis thaliana AtHNL enantioselectivity mutant At-A9-H7 Apo, Y13C,Y121L,P126F,L128W,C131T,F179L,A209I with benzaldehyde,mandelic acid nitrile, 6COG: Structure of the hydroxynitrile lyase from Arabidopsis thaliana AtHNL enantioselectivity mutant At-A9-H7 Apo, Y13C,Y121L,P126F,L128W,C131T,A209I with benzaldehyde, 6COH: Structure of the hydroxynitrile lyase from Arabidopsis thaliana AtHNL enantioselectivity mutant At-A9-H7 Apo, Y13C,Y121L,P126F,L128W,C131T,A209I with benzaldehyde, mandelic acid nitrile, 6COI: Structure of the hydroxynitrile lyase from Arabidopsis thaliana At-A9-H7 Apo, Y13C,Y121L,P126F,L128W,C131T,A209I with cyanide, benzaldehyde, mandelic acid nitrile
Tryptophan 128 of hydroxynitrile lyase of Manihot esculenta (MeHNL) covers a significant part of a hydrophobic channel that gives access to the active site of the enzyme. This residue was therefore substituted in the mutant MeHNL-W128A by alanine to study its importance for the substrate specificity of the enzyme. Wild-type MeHNL and MeHNL-W128A showed comparable activity on the natural substrate acetone cyanohydrin (53 and 40 U/mg, respectively). However, the specific activities of MeHNL-W128A for the unnatural substrates mandelonitrile and 4-hydroxymandelonitrile are increased 9-fold and approximately 450-fold, respectively, compared with the wild-type MeHNL. The crystal structure of the MeHNL-W128A substrate-free form at 2.1 A resolution indicates that the W128A substitution has significantly enlarged the active-site channel entrance, and thereby explains the observed changes in substrate specificity for bulky substrates. Surprisingly, the MeHNL-W128A--4-hydroxybenzaldehyde complex structure at 2.1 A resolution shows the presence of two hydroxybenzaldehyde molecules in a sandwich type arrangement in the active site with an additional hydrogen bridge to the reacting center.