title: From chlorite dismutase towards HemQ - the role of the proximal H-bonding network in haeme binding.
abstract: Chlorite dismutase (Cld) and HemQ are structurally and phylogenetically closely related haeme enzymes differing fundamentally in their enzymatic properties. Clds are able to convert chlorite into chloride and dioxygen, whereas HemQ is proposed to be involved in the haeme b synthesis of Gram-positive bacteria. A striking difference between these protein families concerns the proximal haeme cavity architecture. The pronounced H-bonding network in Cld, which includes the proximal ligand histidine and fully conserved glutamate and lysine residues, is missing in HemQ. In order to understand the functional consequences of this clearly evident difference, specific hydrogen bonds in Cld from 'Candidatus Nitrospira defluvii' (NdCld) were disrupted by mutagenesis. The resulting variants (E210A and K141E) were analysed by a broad set of spectroscopic (UV-vis, EPR and resonance Raman), calorimetric and kinetic methods. It is demonstrated that the haeme cavity architecture in these protein families is very susceptible to modification at the proximal site. The observed consequences of such structural variations include a significant decrease in thermal stability and also affinity between haeme b and the protein, a partial collapse of the distal cavity accompanied by an increased percentage of low-spin state for the E210A variant, lowered enzymatic activity concomitant with higher susceptibility to self-inactivation. The high-spin (HS) ligand fluoride is shown to exhibit a stabilizing effect and partially restore wild-type Cld structure and function. The data are discussed with respect to known structure-function relationships of Clds and the proposed function of HemQ as a coprohaeme decarboxylase in the last step of haeme biosynthesis in Firmicutes and Actinobacteria.
authors: Department for Structural and Computational Biology, Max F. Perutz Laboratories, University of Vienna, A-1030 Vienna, Austria.
authors: Stefan
authors: S
authors: Hofbauer
authors: Dipartimento di Chimica "Ugo Schiff", Università di Firenze, Via della Lastruccia 3-13, I-50019 Sesto Fiorentino (FI), Italy.
authors: Barry D
authors: BD
authors: Howes
authors: Dipartimento di Chimica "Ugo Schiff", Università di Firenze, Via della Lastruccia 3-13, I-50019 Sesto Fiorentino (FI), Italy.
authors: Nicola
authors: N
authors: Flego
authors: Department of Chemistry, Division of Biochemistry, BOKU-University of Natural Resources and Life Sciences, Muthgasse 18, A-1190 Vienna, Austria.
authors: Katharina F
authors: KF
authors: Pirker
authors: Department of Chemistry, Division of Biochemistry, BOKU-University of Natural Resources and Life Sciences, Muthgasse 18, A-1190 Vienna, Austria.
authors: Irene
authors: I
authors: Schaffner
authors: Department for Structural and Computational Biology, Max F. Perutz Laboratories, University of Vienna, A-1030 Vienna, Austria.
authors: Georg
authors: G
authors: Mlynek
authors: Department for Structural and Computational Biology, Max F. Perutz Laboratories, University of Vienna, A-1030 Vienna, Austria Department of Biochemistry, Faculty of Chemistry and Chemical Technology, University of Ljubljana, Aškerčeva 5, 1000 Ljubljana, Slovenia.
authors: Kristina
authors: K
authors: Djinović-Carugo
authors: Department of Chemistry, Division of Biochemistry, BOKU-University of Natural Resources and Life Sciences, Muthgasse 18, A-1190 Vienna, Austria.
authors: Paul G
authors: PG
authors: Furtmüller
authors: Dipartimento di Chimica "Ugo Schiff", Università di Firenze, Via della Lastruccia 3-13, I-50019 Sesto Fiorentino (FI), Italy christian.obinger@boku.ac.at giulietta.smulevich@unifi.it.
authors: Giulietta
authors: G
authors: Smulevich
authors: Department of Chemistry, Division of Biochemistry, BOKU-University of Natural Resources and Life Sciences, Muthgasse 18, A-1190 Vienna, Austria christian.obinger@boku.ac.at giulietta.smulevich@unifi.it.
authors: Christian
authors: C
authors: Obinger
mesh_terms: D019943:Amino Acid Substitution; D001419:Bacteria / Q000201:enzymology* / Q000235:genetics; D001426:Bacterial Proteins / Q000737:chemistry* / Q000235:genetics; D006418:Heme / Q000737:chemistry*; D006860:Hydrogen Bonding; D008956:Models, Chemical; D020125:Mutation, Missense; D010088:Oxidoreductases / Q000737:chemistry* / Q000235:genetics
chemical_list: D001426:Bacterial Proteins; D006418:Heme; D010088:Oxidoreductases; C402794:chlorite dismutase
keywords: H-bonding network; HemQ; chlorite dismutase; electron paramagnetic resonance spectroscopy; haeme binding; resonance Raman spectroscopy