Structure of dihydrodipicolinate synthase of Nicotiana sylvestris reveals novel quaternary structure.

DHDPS is the first enzyme unique to the lysine biosynthetic pathway in plants and bacteria and catalyses the formation of (4S)-4-hydroxy-2,3,4,5-tetrahydro-(2S)-dipicolinic acid. It is feedback-regulated in plants by L-lysine. The crystal structure of Nicotiana sylvestris DHDPS with and without inhibitory lysine bound to the enzyme has been solved to a resolution of 2.8 A. The molecule is a homotetramer composed of a dimer of dimers. Comparison with the structure of Escherichia coli DHDPS showed a novel quaternary structure by a profound rearrangement of the dimers forming the tetramer. The crystal structure of the enzyme in the presence of L-lysine revealed substantial changes. These changes together with the novel quaternary structure provide a structural basis for the strong inhibition of plant DHDPS enzymes by L-lysine.