title: Role of Ionic Strength and pH in Modulating Thermodynamic Profiles Associated with CO Escape from Rice Nonsymbiotic Hemoglobin 1.
abstract: Type 1 nonsymbiotic hemoglobins are found in a wide variety of land plants and exhibit very high affinities for exogenous gaseous ligands. These proteins are presumed to have a role in protecting plant cells from oxidative stress under etiolated/hypoxic conditions through NO dioxygenase activity. In this study we have employed photoacoustic calorimetry, time-resolved absorption spectroscopy, and classical molecular dynamics simulations in order to elucidate thermodynamics, kinetics, and ligand migration pathways upon CO photodissociation from WT and a H73L mutant of type 1 nonsymbiotic hemoglobin from Oryza sativa (rice). We observe a temperature dependence of the resolved thermodynamic parameters for CO photodissociation from CO-rHb1 which we attribute to temperature dependent formation of a network of electrostatic interactions in the vicinity of the heme propionate groups. We also observe slower ligand escape from the protein matrix under mildly acidic conditions in both the WT and H73L mutant (τ = 134 ± 19 and 90 ± 15 ns). Visualization of transient hydrophobic channels within our classical molecular dynamics trajectories allows us to attribute this phenomenon to a change in the ligand migration pathway which occurs upon protonation of the distal His73, His117, and His152. Protonation of these residues may be relevant to the functioning of the protein in vivo given that etiolation/hypoxia can cause a decrease in intracellular pH in plant cells.
authors.affiliation: Department of Chemistry and Biochemistry, Florida International University , Miami Florida 33199, United States.
authors.forename: David
authors.initials: D
authors.lastname: Butcher
authors.affiliation: Laboratoire de Chimie Physique, Université Paris-Sud 11 , 91405 Orsay, France.
authors.forename: Sophie
authors.initials: S
authors.lastname: Bernad
authors.affiliation: Laboratoire de Chimie Physique, Université Paris-Sud 11 , 91405 Orsay, France.
authors.forename: Valerie
authors.initials: V
authors.lastname: Derrien
authors.affiliation: Laboratoire de Chimie Physique, Université Paris-Sud 11 , 91405 Orsay, France.
authors.forename: Pierre
authors.initials: P
authors.lastname: Sebban
authors.affiliation: Department of Chemistry and Biochemistry, Florida International University , Miami Florida 33199, United States.|Biomolecular Sciences Institute, Florida International University , Miami, Florida 33199, United States.
authors.forename: Jaroslava
authors.identifier: 0000-0002-0385-9457
authors.initials: J
authors.lastname: Miksovska
mesh_terms: D002151:Calorimetry; D002248:Carbon Monoxide / Q000737:chemistry / Q000378:metabolism* / Q000528:radiation effects; D006418:Heme / Q000737:chemistry / Q000528:radiation effects; D006420:Hemeproteins / Q000737:chemistry / Q000378:metabolism* / Q000528:radiation effects; D006639:Histidine / Q000737:chemistry; D006863:Hydrogen-Ion Concentration; D007501:Iron / Q000737:chemistry; D007700:Kinetics; D008024:Ligands; D056004:Molecular Dynamics Simulation; D012275:Oryza; D009994:Osmolar Concentration; D010940:Plant Proteins / Q000737:chemistry / Q000378:metabolism* / Q000528:radiation effects; D011485:Protein Binding; D011487:Protein Conformation; D013696:Temperature; D013816:Thermodynamics
chemical_list: D006420:Hemeproteins; D008024:Ligands; D010940:Plant Proteins; D006418:Heme; D006639:Histidine; D002248:Carbon Monoxide; D007501:Iron