Evidence for fast conformational change upon ligand dissociation in the HemAT class of bacterial oxygen sensors |
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Authors: | Mokdad Audrey Nissen Mark Satterlee James D Larsen Randy W |
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Affiliation: | Department of Chemistry, University of South Florida, 4202 East Fowler Ave., Tampa, FL 33620, United States. |
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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. |
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Keywords: | HemAT-Bs Photoacoustic calorimtery Heme Signaling Aerotaxis |
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