title: Kinetic Control of O2 Reactivity in H-NOX Domains.
abstract: Transient absorption, resonance Raman, and vibrational coherence spectroscopies are used to investigate the mechanisms of NO and O2 binding to WT Tt H-NOX and its P115A mutant. Vibrational coherence spectra of the oxy complexes provide clear evidence for the enhancement of an iron-histidine mode near 217 cm(-1) following photoexcitation, which indicates that O2 can be dissociated in these proteins. However, the quantum yield of O2 photolysis is low, particularly in the wild type (≲3%). Geminate recombination of O2 and NO in both of these proteins is very fast (∼1.4 × 10(11) s(-1)) and highly efficient. We show that the distal heme pocket of the H-NOX system forms an efficient trap that limits the O2 off-rate and determines the overall affinity. The distal pocket hydrogen bond, which appears to be stronger in the P115A mutant, may help retard the O2 ligand from escaping into the solvent following either photoinduced or thermal dissociation. This, along with a strengthening of the Fe-O2 bond that is correlated with the significant heme ruffing and saddling distortions, explains the unusually high O2 affinity of WT Tt H-NOX and the even higher affinity found in the P115A mutant.
authors.affiliation: Department of Physics and Center for Interdisciplinary Research on Complex Systems, Northeastern University , Boston, Massachusetts 02115, United States.
authors.forename: Yuhan
authors.initials: Y
authors.lastname: Sun
authors.affiliation: Department of Physics and Center for Interdisciplinary Research on Complex Systems, Northeastern University , Boston, Massachusetts 02115, United States.
authors.forename: Abdelkrim
authors.initials: A
authors.lastname: Benabbas
authors.affiliation: Department of Physics and Center for Interdisciplinary Research on Complex Systems, Northeastern University , Boston, Massachusetts 02115, United States.
authors.forename: Weiqiao
authors.initials: W
authors.lastname: Zeng
authors.affiliation: Department of Chemistry and the Institute of Chemical Biology and Drug Discovery, Stony Brook University , Stony Brook, New York 11794, United States.
authors.forename: Sandhya
authors.initials: S
authors.lastname: Muralidharan
authors.affiliation: Department of Chemistry and the Institute of Chemical Biology and Drug Discovery, Stony Brook University , Stony Brook, New York 11794, United States.
authors.forename: Elizabeth M
authors.initials: EM
authors.lastname: Boon
authors.affiliation: Department of Physics and Center for Interdisciplinary Research on Complex Systems, Northeastern University , Boston, Massachusetts 02115, United States.
authors.forename: Paul M
authors.initials: PM
authors.lastname: Champion
mesh_terms: D001426:Bacterial Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D006162:Guanylate Cyclase / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D007700:Kinetics; D016297:Mutagenesis, Site-Directed; D009569:Nitric Oxide / Q000737:chemistry / Q000378:metabolism; D010100:Oxygen / Q000737:chemistry* / Q000378:metabolism; D000072417:Protein Domains; D011789:Quantum Theory; D013059:Spectrum Analysis, Raman; D014734:Vibrio cholerae / Q000201:enzymology
chemical_list: D001426:Bacterial Proteins; D009569:Nitric Oxide; D006162:Guanylate Cyclase; D010100:Oxygen