The 2-His-1-carboxylate facial triad is a common metal binding motif among nonheme iron(II) enzymes. Made up of two histidine side chain residues, and one carboxylate side chain of either a glutamate or aspartate residue occupying one face of the iron(II) octahedral coordinating sphere, the 2-His-1-carboxylate motif provides proximity of substrate(s) and molecular oxygen for important oxidation reactions in biological chemistry. Computational, structural, and kinetic analyses have afforded mechanistic details on how these enzymes control the oxidation reactions they catalyze; from the oxidation state of the metal center to the supporting interactions from secondary sphere amino acid residues. However, the extensive literature on the 2-His-1-carboxylate facial triad enzymes currently contains deficiencies in the area of fundamental, experimental thermodynamic analyses of metal and substrate binding in these systems. The focus of this study is to determine the energetics of substrate and metal binding to two representative enzymes of the 2-His-1-carboxylate facial triad-containing family. More specifically, we examine iron(II) binding to the alpha-ketoglutarate- dependent model system alpha-ketoglutarate/taurine dioxygenase, and substrate binding to a well-known extradiol dioxygenase, homoprotocatechuate 2,3-dioxygenase. Using isothermal titration calorimetry, we are able to determine equilibrium constants, enthalpies, entropies and Gibbs free energies for the binding reactions, affording new insight into what drives the reactions forward at the 2-His-1-carboxylate facial triad active site center.
| Identifer | oai:union.ndltd.org:MSSTATE/oai:scholarsjunction.msstate.edu:td-5708 |
| Date | 09 May 2015 |
| Creators | Henderson, Kate Lynne |
| Publisher | Scholars Junction |
| Source Sets | Mississippi State University |
| Detected Language | English |
| Type | text |
| Format | application/pdf |
| Source | Theses and Dissertations |
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