The crystal structures of both isoforms of the aminoaldehyde dehydrogenase from pea (PsAMADH) have been solved recently [Tylichováet al. (2010) J Mol Biol396, 870-882]. The characterization of the PsAMADH2 proteins, altered here by site-directed mutagenesis, suggests that the D110 and D113 residues at the entrance to the substrate channel are required for high-affinity binding of ω-aminoaldehydes to PsAMADH2 and for enzyme activity, whereas N162, near catalytic C294, contributes mainly to the enzyme's catalytic rate. Inside the substrate cavity, W170 and Y163, and, to a certain extent, L166 and M167 probably preserve the optimal overall geometry of the substrate channel that allows for the appropriate orientation of the substrate. Unconserved W288 appears to affect the affinity of the enzyme for the substrate amino group through control of the substrate channel diameter without affecting the reaction rate. Therefore, W288 may be a key determinant of the differences in substrate specificity found among plant AMADH isoforms when they interact with naturally occurring substrates such as 3-aminopropionaldehyde and 4-aminobutyraldehyde.

Department of Protein Biochemistry and Proteomics Centre of the Region Haná for Biotechnological and Agricultural Research Faculty of Science Palacký University Olomouc Czech Republic

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