CHED 801 |
| The FixL protein from S. meliloti is a heme-based oxygen sensor that is part of a two component regulatory system in alfalfa plants that regulates nitrogen fixation and microaerobic respiration in response to fluctuations in the level of oxygen. It is known that the binding of oxygen to the heme iron PAS domain to form the oxy, “off” state shuts off the activity of the kinase domain. When oxygen is not bound to the heme, the kinase domain is activated and phosphorylates FixJ, the transcriptional activator of the nif genes. Although the wild-type protein has been characterized with a variety of biochemical and spectroscopic techniques, the detailed mechanism by which oxygen binding is sensed and how it regulates the kinase domain is not well understood. Our research looks at the role of several conserved amino acids in the F helix which contains the proximal heme ligand H194. We have purified and characterized the site-directed mutants (R200A, R200E, R200H, R200I, R200Q), Y197A, and Y201A. Our studies show that the charge and size at R200 is crucial for oxygen binding and stability and may be important in transmitting this information to the kinase domain of FixL. Y197A rapidly autoxidizes while Y201F loses heme suggesting that these residues are important for binding oxygen and heme, respectively. |
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Undergraduate Research Poster Session: Biochemistry
2:00 PM-4:00 PM, Monday, April 7, 2008 Morial Convention Center -- Hall A, Poster
Division of Chemical Education |