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 curd catalyses the formation of (4S)-4-hydroxy-2, 3,4,5-tetrahydro-(2S)-dipicolinic acid. It is feedback-regulated in pl ants 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 Angstrom. The molecule is a homotetramer compo sed of a : dimer of dimers, Comparison with the structure of Escherich ia coli DHDPS showed a novel quaternary structure by a profound rearra ngement of the dimers forming the tetramer. The crystal structure of t he enzyme in the presence of L-lysine revealed substantial changes. Th ese changes together with the novel quaternary structure provide a str uctural basis for the strong inhibition of plant DHDPS enzymes by L-ly sine. (C) 1997 Academic Press Limited.