Plant Physiol, June 2001, Vol. 126, pp. 631-642

The Three-Dimensional Structure of Cystathionine -Lyase from Arabidopsis and Its Substrate Specificity

Max-Planck-Institut für Biochemie, Abteilung Strukturforschung, Am Klopferspitz 18a, D-82152 Martinsried, Germany (U.B., T.C., S.E., R.H., A.M.); Aventis CropScience, Forschung Biochemie, Industriepark Hoechst, H872N, 65926 Frankfurt am Main, Germany (B.L.); Aventis CropScience UK, Biochemical Research, Fyfield Road, Ongar, Essex CM5 0HW, United Kingdom (F.S.); and EMBL Outstation Hamburg, c/o DESY Notkestrasse 85, Gebäude 25a, D-22603 Hamburg, Germany (E.P.)

The pyridoxal 5'-phosphate-dependent enzyme cystathionine -lyase (CBL) catalyzes the penultimate step in the de novo biosynthesis of Met in microbes and plants. Absence of CBL in higher organisms makes it an important target for the development of antibiotics and herbicides. The three-dimensional structure of cystathionine -lyase from Arabidopsis was determined by Patterson search techniques, using the structure of tobacco (Nicotiana tabacum) cystathionine -synthase as starting point. At a resolution of 2.3 Å, the model was refined to a final crystallographic R-factor of 24.9%. The overall structure is very similar to other pyridoxal 5'-phosphate-dependent enzymes of the -family. Exchange of a few critical residues within the active site causes the different substrate preferences between Escherichia coli and Arabidopsis CBL. Loss of interactions at the -carboxyl site is the reason for the poorer substrate binding of Arabidopsis CBL. In addition, the binding pocket of Arabidopsis CBL is larger than that of E. coli CBL, explaining the similar binding of L-cystathionine and L-djenkolate in Arabidopsis CBL in contrast to E. coli CBL, where the substrate binding site is optimized for the natural substrate cystathionine.