Crystal structure of dihydrodipicolinate synthase from Hahella chejuensis at 1.5 A resolution.

Lysine biosynthesis has been of interest in plant research, because lysine is the most limiting amino acid in crop protein production. Dihydrodipicolinate synthase (DHDPS) catalyzes the branch point reaction leading to meso-diaminopimelate (DAP) and (S)-lysine in lysine biosynthesis. In this report, we present the crystal structure of DHDPS from the marine bacterium Hahella chejuensis (HcDHDPS) at 1.5 A resolution. The four subunits of the asymmetric unit assemble to form a tetramer with an approximate 222 symmetry. At the active site of HcDHDPS, three residues Tyr132, Thr43 and Tyr106 are observed to constitute a catalytic triad and are located at similar positions of the corresponding residues of Escherichia coli DHDPS. The structural similarities in the overall fold and the active site environment between these two enzymes imply that HcDHDPS functions by a mechanism similar to E. coli DHDPS. However, unlike E. coli DHDPS, HcDHDPS has a unique extensive dimer-dimer interface that is mediated by not only strong hydrophobic interactions but also a hydrogen bond network.