Allostery in the nitric oxide dioxygenase mechanism of flavohemoglobin
| Autor: | Anne M. Gardner, Paul R. Gardner |
|---|---|
| Rok vydání: | 2020 |
| Předmět: |
0301 basic medicine
Models Molecular Protein Conformation TMAO trimethylamine-N-oxide flavoHb flavohemoglobin Biochemistry chemistry.chemical_compound Dihydropteridine Reductase NADH NADPH Oxidoreductases heme Heme Mb myoglobin Escherichia coli Infections allostery LT long tunnel Escherichia coli Proteins Nitric oxide dioxygenase flavin electron transfer Myoglobin Φdis photodissociation Oxygenases nitric oxide dioxygenase Cygb cytoglobin Ngb neuroglobin Research Article ET electron transfer Allosteric regulation Kinetics Flavin group Nitric Oxide 03 medical and health sciences Electron transfer Allosteric Regulation Escherichia coli Humans Molecular Biology τT transition time 030102 biochemistry & molecular biology ST short tunnel Cell Biology hemoglobin WT wild-type 030104 developmental biology chemistry flavohemoglobin myoglobin Biophysics BSA bovine serum albumin oxygen Oxygen binding Hb hemoglobin |
| Zdroj: | The Journal of Biological Chemistry |
| ISSN: | 1083-351X |
| Popis: | The substrates O2 and NO cooperatively activate the NO dioxygenase function of Escherichia coli flavohemoglobin. Steady-state and transient kinetic measurements support a structure-based mechanistic model in which O2 and NO movements and conserved amino acids at the E11, G8, E2, E7, B10, and F7 positions within the globin domain control activation. In the cooperative and allosteric mechanism, O2 migrates to the catalytic heme site via a long hydrophobic tunnel and displaces LeuE11 away from the ferric iron, which forces open a short tunnel to the catalytic site gated by the ValG8/IleE15 pair and LeuE11. NO permeates this tunnel and leverages upon the gating side chains triggering the CD loop to furl, which moves the E and F-helices and switches an electron transfer gate formed by LysF7, GlnE7, and water. This allows FADH2 to reduce the ferric iron, which forms the stable ferric–superoxide–TyrB10/GlnE7 complex. This complex reacts with internalized NO with a bimolecular rate constant of 1010 M−1 s−1 forming nitrate, which migrates to the CD loop and unfurls the spring-like structure. To restart the cycle, LeuE11 toggles back to the ferric iron. Actuating electron transfer with O2 and NO movements averts irreversible NO poisoning and reductive inactivation of the enzyme. Together, structure snapshots and kinetic constants provide glimpses of intermediate conformational states, time scales for motion, and associated energies. |
| Databáze: | OpenAIRE |
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