| Budget Amount *help |
¥15,700,000 (Direct Cost: ¥15,700,000)
Fiscal Year 2006: ¥3,800,000 (Direct Cost: ¥3,800,000)
Fiscal Year 2005: ¥3,800,000 (Direct Cost: ¥3,800,000)
Fiscal Year 2004: ¥8,100,000 (Direct Cost: ¥8,100,000)
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| Research Abstract |
Hemeproteins show a wide variety of functions including storage and transport of molecular oxygen, electron transfer, and redox catalysis of various substrates. Besides these traditional functions, a new function of hemeproteins has been found recently, in which the heme acts as a sensor of diatomic gas molecules such as oxygen, nitric oxide, and carbon monoxide. In this work, the structure and function relationships was studied for an oxygen sensor protein (HemAT-Bs) and CO-sensor proteins (Rr-CooA and Ch-CooA).
CooA is a CO sensing transcriptional activator, which contains a b-type heme as the active site for sensing its physiological effector, CO. CooA from Rhodospirillum rubrum (Rr-CooA) shows some unique properties for the coordination structure of the heme. However, it is not clear if these unique properties are essential for CooA function. To determine the essential elements for CooA function, I have characterized a CooA homologue from Carboxydothermus hydrogenoformans (Ch-CooA) by spectroscopic and mutagenesis studies in this work. Comparing the properties of Ch-CooA and Rr-CooA provides that the essential elements for CooA function will be that (i) the heme is six-coordinate in the Fe(III), Fe(II), and Fe(II)-CO forms ; (ii) the 1'4-tern-films is coordinated to the heme as an axial ligand ; and (iii) CO replaces the N-terminus bound to the heme upon CO binding.
HemAT-Bs is a signal transducer protein responsible for aerotaxis of B. subtilis. The recombinant HemAT-Bs shows similar spectroscopic properties to Mb. However, HemAT-Bs shows a unique resonance Raman spectrum in the O_2-bound form suggesting a unique hydrogen bonding network between the heme-bound oxygen and distal amino acid residues in the distal heme pocket. Thr95 is involved in the hydrogen bonding to the heme-bound oxygen. Resonance Raman spectroscopy reveals that there are three different conformations in the O_2-bound form of HemAT-Bs.
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