title: Tautomeric state and pKa of the phosphorylated active site histidine in the N-terminal domain of enzyme I of the Escherichia coli phosphoenolpyruvate:sugar phosphotransferase system.
abstract: The phosphorylated form of the N-terminal domain of enzyme I of the phosphoenolpyruvate:sugar phosphotransferase system of Escherichia coli has been investigated by one-bond and long-range 1H-15N correlation spectroscopy. The active site His 189 is phosphorylated at the Nepsilon2 position and has a pKa of 7.3, which is one pH unit higher than that of unphosphorylated His 189. Because the neutral form of unphosphorylated His 189 is in the Ndelta1-H tautomer, and its Nepsilon2 atom is solvent inaccessible and accepts a hydrogen bond from the hydroxyl group of Thr 168, both protonation and phosphorylation of His 189 must be accompanied by a change in the side-chain conformation of His 189, specifically from a chi(2) angle in the g+ conformer in the unphosphorylated state to the g- conformer in the phosphorylated state.
authors.affiliation: Laboratory of Chemical Physics, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Bethesda, Maryland 20892-0520, USA.
authors.forename: D S
authors.initials: DS
authors.lastname: Garrett
authors.forename: Y J
authors.initials: YJ
authors.lastname: Seok
authors.forename: A
authors.initials: A
authors.lastname: Peterkofsky
authors.forename: G M
authors.initials: GM
authors.lastname: Clore
authors.forename: A M
authors.initials: AM
authors.lastname: Gronenborn
mesh_terms: D001426:Bacterial Proteins / Q000737:chemistry; D001665:Binding Sites; D004926:Escherichia coli / Q000201:enzymology*; D006639:Histidine / Q000737:chemistry; D008958:Models, Molecular; D019906:Nuclear Magnetic Resonance, Biomolecular; D010731:Phosphoenolpyruvate Sugar Phosphotransferase System / Q000737:chemistry*; D010766:Phosphorylation; D017434:Protein Structure, Tertiary
chemical_list: D001426:Bacterial Proteins; D006639:Histidine; D010731:Phosphoenolpyruvate Sugar Phosphotransferase System