title: Titration of E. coli transhydrogenase domain III with bound NADP+ or NADPH studied by NMR reveals no pH-dependent conformational change in the physiological pH range.
abstract: A pH-titration 2D NMR study of Escherichia coli transhydrogenase domain III with bound NADP(+) or NADPH has been carried out, in which the pH was varied between 5.4 and 12. In this analysis, individual amide protons served as reporter groups. The apparent pK(a) values of the amide protons, determined from the pH-dependent chemical shift changes, were attributed to actual pK(a) values for several titrating residues in the protein. The essential Asp392 is shown to be protonated at neutral pH in both the NADP(+) and NADPH forms of domain III, but with a marked difference in pK(a) not only attributable to the charge difference between the substrates. Titrating residues found in loop D/alpha5 point to a conformational difference of these structural elements that is redox-dependent, but not pH dependent. The observed apparent pK(a) values of these residues are discussed in relation to the crystal structure of Rhodospirillum rubrum domain III, the solution structure of E. coli domain III and the mechanism of intact proton-translocating transhydrogenase.
authors.affiliation: Department of Chemistry, Göteborg University, P.O. Box 462, SE-405 30 Göteborg, Sweden.
authors.forename: Anders
authors.initials: A
authors.lastname: Pedersen
authors.forename: Tomas
authors.initials: T
authors.lastname: Johansson
authors.forename: Jan
authors.initials: J
authors.lastname: Rydström
authors.forename: B
authors.initials: B
authors.lastname: Göran Karlsson
mesh_terms: D029968:Escherichia coli Proteins / Q000737:chemistry*; D006863:Hydrogen-Ion Concentration; D009249:NADP / Q000737:chemistry / Q000378:metabolism; D009250:NADP Transhydrogenases / Q000737:chemistry*; D019906:Nuclear Magnetic Resonance, Biomolecular; D010084:Oxidation-Reduction; D017434:Protein Structure, Tertiary; D021122:Protein Subunits / Q000737:chemistry; D017186:Titrimetry
chemical_list: D029968:Escherichia coli Proteins; D021122:Protein Subunits; D009249:NADP; D009250:NADP Transhydrogenases