title: Probing the role of metal ions in the catalysis of Helicobacter pylori 3-deoxy-D-manno-octulosonate-8-phosphate synthase using a transient kinetic analysis.
abstract: 3-Deoxy-d-manno-2-octulosonate-8-phosphate (KDO8P) synthase catalyzes the net condensation of phosphoenolpyruvate and d-arabinose 5-phosphate to form KDO8P and inorganic phosphate (Pi). Two classes of KDO8P synthases have been identified. The Class I KDO8P synthases (e.g. Escherchia coli KDO8P synthase) catalyze the condensation reaction in a metal-independent fashion, whereas the Class II enzymes (e.g. Aquifex aeolicus) require metal ions for catalysis. Helicobacter pylori (H. pylori) KDO8P synthase, a Zn2+-dependent metalloenzyme, has recently been found to be a Class II enzyme and has a high degree of clinical significance since it is an attractive molecular target for the design of novel antibiotic therapy. Although the presence of a divalent metal ion in Class II KDO8P synthases is essential for catalysis, there is a paucity of mechanistic information on the role of the metal ions and functional differences as compared with Class I enzymes. Using H. pylori KDO8P synthase as a prototypical Class II enzyme, a steady-state and transient kinetic approach was undertaken to understand the role of the metal ion in catalysis and define the kinetic reaction pathway. Metal reconstitution experiments examining the reaction kinetics using Zn2+, Cd2+, Cu2+, Co2+, Mn2+, and Ni2+ yielded surprising results in that the Cd2+ enzyme has the greatest activity. Unlike Class-I KDO8P synthases, the Class II metallo-KDO8P synthases containing Zn2+, Cd2+, Cu2+, and Co2+ show cooperativity. This study presents the first detailed kinetic characterization of a metal-dependent Class II KDO8P synthase and offers mechanistic insight for how the divalent metal ions modulate catalysis through effects on chemistry as well as quaternary protein structure.
authors.affiliation: Department of Pharmacology, Yale University School of Medicine, New Haven, Connecticut 06520, USA.
authors.forename: Apurba Kumar
authors.initials: AK
authors.lastname: Sau
authors.forename: Zhili
authors.initials: Z
authors.lastname: Li
authors.forename: Karen S
authors.initials: KS
authors.lastname: Anderson
mesh_terms: D000446:Aldehyde-Lyases / Q000737:chemistry / Q000378:metabolism*; D001665:Binding Sites; D002384:Catalysis; D004795:Enzyme Stability; D016480:Helicobacter pylori / Q000201:enzymology*; D007700:Kinetics; D008670:Metals / Q000378:metabolism; D013379:Substrate Specificity
chemical_list: D008670:Metals; C020011:2-dehydro-3-deoxyphosphooctonate aldolase; D000446:Aldehyde-Lyases