title: Evidence for fast conformational change upon ligand dissociation in the HemAT class of bacterial oxygen sensors.
abstract: Here we report the results of transient absorption and photoacoustic calorimetry studies of CO photodissociation from the heme domain of the bacterial oxygen sensor HemAT-Bs. The results indicate that CO photolysis is accompanied by an overall DeltaH of -19 kcal mol(-1) and DeltaV of +4 ml mol(-1) as well as a red-shifted kinetic difference spectrum all occurring in <50 ns. Analysis of the DeltaH/DeltaV reveals that a conformational change takes place with a DeltaH(conf) of -40 kcal mol(-1) and DeltaV(conf) of -22 ml mol(-1). These thermodynamic changes are consistent with an increase in the solvent accessible surface area of the protein upon ligand dissociation, as observed in the X-ray structure of the ferric CN-bound and CN free forms of HemAT-Bs.
authors.affiliation: Department of Chemistry, University of South Florida, 4202 East Fowler Ave., Tampa, FL 33620, United States.
authors.forename: Audrey
authors.initials: A
authors.lastname: Mokdad
authors.forename: Mark
authors.initials: M
authors.lastname: Nissen
authors.forename: James D
authors.initials: JD
authors.lastname: Satterlee
authors.forename: Randy W
authors.initials: RW
authors.lastname: Larsen
mesh_terms: D001426:Bacterial Proteins / Q000737:chemistry* / Q000378:metabolism; D002151:Calorimetry; D002248:Carbon Monoxide / Q000737:chemistry / Q000378:metabolism; D006418:Heme / Q000737:chemistry / Q000378:metabolism; D006420:Hemeproteins / Q000737:chemistry* / Q000378:metabolism; D008024:Ligands; D008958:Models, Molecular; D010100:Oxygen / Q000737:chemistry* / Q000378:metabolism; D011485:Protein Binding; D011487:Protein Conformation; D013816:Thermodynamics
chemical_list: D001426:Bacterial Proteins; D006420:Hemeproteins; D008024:Ligands; D006418:Heme; D002248:Carbon Monoxide; D010100:Oxygen