title: The C-terminal domain of Escherichia coli dihydrodipicolinate synthase (DHDPS) is essential for maintenance of quaternary structure and efficient catalysis.
abstract: Dihydrodipicolinate synthase (DHDPS) catalyses the first committed step in the biosynthesis of (S)-lysine, an essential constituent of bacterial cell walls. Escherichia coli DHDPS is homotetrameric, and each monomer contains an N-terminal (alpha/beta)(8)-barrel, responsible for catalysis and regulation, and three C-terminal alpha-helices, the function of which is unknown. This study investigated the C-terminal domain of E. coli DHDPS by characterising a C-terminal truncated DHDPS (DHDPS-H225*). DHDPS-H225* was unable to complement an (S)-lysine auxotroph, and showed significantly reduced solubility, stability, and maximum catalytic activity (k(cat)=1.20+/-0.01 s(-1)), which was only 1.6% of wild type E. coli DHDPS (DHDPS-WT). The affinity of DHDPS-H225* for substrates and the feedback inhibitor, (S)-lysine, remained comparable to DHDPS-WT. These changes were accompanied by disruption in the quaternary structure, which has previously been shown to be essential for efficient catalysis in this enzyme.
authors.affiliation: School of Biological Sciences, University of Canterbury, Private Bag 4800, Ilam, Christchurch, Canterbury 4800, New Zealand.
authors.forename: Belinda B B
authors.initials: BB
authors.lastname: Guo
authors.forename: Sean R A
authors.initials: SR
authors.lastname: Devenish
authors.forename: Renwick C J
authors.initials: RC
authors.lastname: Dobson
authors.forename: Andrew C
authors.initials: AC
authors.lastname: Muscroft-Taylor
authors.forename: Juliet A
authors.initials: JA
authors.lastname: Gerrard