A MOLECULAR-MODEL FOR CINNAMYL ALCOHOL-DEHYDROGENASE, A PLANT AROMATIC ALCOHOL-DEHYDROGENASE INVOLVED IN LIGNIFICATION

The plant aromatic alcohol dehydrogenase, cinnamyl alcohol dehydrogena se (CAD2 from Eucalyptus) was found by sequence analysis of its cloned gene to be homologous to a range of dehydrogenases including alcohol dehydrogenases, L-threonine-3-dehydrogenase, D-xylose reductase and so rbitol dehydrogenase. A homology model of CAD2 was built using the X-r ay crystallographic coordinates of horse-liver alcohol dehydrogenase t o provide the template, with additional modelling input from other ana logous regions of structure from similar enzymes where necessary. The structural model thus produced rationalised the Zn-binding properties of CAD2, indicated the possession of a Rossmann fold (GXGXXG motif), a nd explained the class A stereospecificity (pro-R hydrogen removal fro m substrate alcohol) and aromatic substrate specificity of the enzyme. A range of potential ligands was designed based on the homology model and tested as inhibitors of CAD2 and horse liver alcohol dehydrogenas e.