2CF5

Crystal Structures of the Arabidopsis Cinnamyl Alcohol Dehydrogenases, AtCAD5

Summary for 2CF5

• Entry DOI: 10.2210/pdb2cf5/pdb
• Related: 2CF6
• Descriptor: CINNAMYL ALCOHOL DEHYDROGENASE, ZINC ION (3 entities in total)
• Functional Keywords: lignin biosynthesis, metal-binding, nadp, oxidoreductase, zinc
• Biological source: ARABIDOPSIS THALIANA (MOUSE EAR CRESS)
• Total number of polymer chains: 1
• Total formula weight: 38917.49

Authors

Youn, B.,Camacho, R.,Moinuddin, S.,Lee, C.,Davin, L.B.,Lewis, N.G.,Kang, C. (deposition date: 2006-02-16, release date: 2007-02-20, Last modification date: 2023-12-13)

Primary citation

Youn, B.,Camacho, R.,Moinuddin, S.,Lee, C.,Davin, L.B.,Lewis, N.G.,Kang, C.
Crystal Structures and Catalytic Mechanisms of the Arabidopsis Cinnamyl Alcohol Dehydrogenases Atcad5 and Atcad4
Org.Biomol.Chem., 4:1687-, 2006

PubMed Abstract: The cinnamyl alcohol dehydrogenase (CAD) multigene family in planta encodes proteins catalyzing the reductions of various phenylpropenyl aldehyde derivatives in a substrate versatile manner, and whose metabolic products are the precursors of structural lignins, health-related lignans, and various other metabolites. In Arabidopsis thaliana, the two isoforms, AtCAD5 and AtCAD4, are the catalytically most active being viewed as mainly involved in the formation of guaiacyl/syringyl lignins. In this study, we determined the crystal structures of AtCAD5 in the apo-form and as a binary complex with NADP+, respectively, and modeled that of AtCAD4. Both AtCAD5 and AtCAD4 are dimers with two zinc ions per subunit and belong to the Zn-dependent medium chain dehydrogenase/reductase (MDR) superfamily, on the basis of their overall 2-domain structures and distribution of secondary structural elements. The catalytic Zn2+ ions in both enzymes are tetrahedrally coordinated, but differ from those in horse liver alcohol dehydrogenase since the carboxyl side-chain of Glu70 is ligated to Zn2+ instead of water. Using AtCAD5, site-directed mutagenesis of Glu70 to alanine resulted in loss of catalytic activity, thereby indicating that perturbation of the Zn2+ coordination was sufficient to abolish catalytic activity. The substrate-binding pockets of both AtCAD5 and AtCAD4 were also examined, and found to be significantly different and smaller compared to that of a putative aspen sinapyl alcohol dehydrogenase (SAD) and a putative yeast CAD. While the physiological roles of the aspen SAD and the yeast CAD are uncertain, they nevertheless have a high similarity in the overall 3D structures to AtCAD5 and 4. With the bona fide CAD's from various species, nine out of the twelve residues which constitute the proposed substrate-binding pocket were, however, conserved. This is provisionally considered as indicative of a characteristic fingerprint for the CAD family.

PubMed: 16633561
DOI: 10.1039/B601672C

Experimental method

X-RAY DIFFRACTION (2 Å)