Evidence for fast conformational change upon ligand dissociation in the HemAT class of bacterial oxygen sensors.
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.
Mokdad
Audrey
A
Department of Chemistry, University of South Florida, 4202 East Fowler Ave., Tampa, FL 33620, United States.
Nissen
Mark
M
Satterlee
James D
JD
Larsen
Randy W
RW
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
D001426:Bacterial Proteins; D006420:Hemeproteins; D008024:Ligands; D006418:Heme; D002248:Carbon Monoxide; D010100:Oxygen