ESCHERICHIA-COLI DIHYDRODIPICOLINATE SYNTHASE - IDENTIFICATION OF THE ACTIVE-SITE AND CRYSTALLIZATION

Escherichia coli dihydrodipicolinate synthase (DHDPS) (EC 4.2.1.52), the first enzyme unique to lysine biosynthesis, catalyses the condensation of pyruvate and aspartate beta-semialdehyde (ASA) by a ping-pong mechanism. Pyruvate binds first to the enzyme, forming a Schiff base with the epsilon-amino group of Lys-161, followed by binding of ASA. K(m) values of 0.57 and 0.55 mm were determined for pyruvate and DL-ASA respectively. 3-Bromopyruvate inhibits DHDPS with a K(i) of 1.6 mm. DHDPS is 50 % inhibited by 1.0 mM-L-lysine, 1.2 mM-sodium dipicolinate or 4.6 mM-S-2-aminoethyl-L-cysteine. Crystals of DHDPS diffracting to beyond a resolution of 0.24 nm (2.4 angstrom) were obtained under several experimental conditions. Diffraction patterns were compatible with trigonal space groups P3(1)21 or P3(2)21, with unit-cell parameters a = h = 12.26 nm and c = 11. 19 nm. The density of the crystals indicates the presence of a dimer of DHDPS subunits per asymmetric unit.