Thiol dioxygenases are metalloenzymes specialized in catalyzing the conversion of thiol substrates into sulfinic acids. The build-up of thiol molecules, such as 3-mercaptopropionic acid, have been found to induce epileptic activity, as well as neurodegenerative disorders. Cysteine dioxygenase (CDO), a well-characterized second mammalian thiol dioxygenase, contains a 3-histidine (3-His) coordination environment rather than the 2-His-1-carboxylate facial triad seen in most mononuclear non-heme Fe<sup>II</sup> enzymes. Similarly, a bacterial thiol dioxygenase, 3-mercaptopropionate dioxygenase (MDO), also contains a 3-His active site that turns over 3-mercaptopropionate (3MPA) into 3-sulfinopropionic acid as part of the sulfur metabolism pathway. The previous characterization of substrate-bound CDO via magnetic circular dichroism (MCD) informs our analysis of the geometric and electronic structure of wild type and mutant MDO. The variants analyzed via MCD clarify the role that secondary sphere amino acid residues play in binding 3MPA to the Fe active site.<br/><br/>The active site of wild-type MDO has a tyrosine residue with a distance of 4.1 Å from the iron, and a histidine residue 5.6 Å from the iron. To understand the role that these residues play in binding 3-MPA to the MDO active site, two variants were generated. The first has a mutation that replaces the tyrosine residue with a phenylalanine (Y159F) and the second replaces the histidine with an asparagine (H157N). Our spectroscopic results obtained for the Y159F variant indicate that the proximity of the tyrosine hydroxyl group influences the binding of 3-MPA.

Magnetic circular dichroism characterization of 3-mercaptopropionate dioxygenase variants

2019 Spring National Meeting

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