Date of Completion

2017

Document Type

Honors College Thesis

Department

Chemistry

Type of Thesis

Honors College

First Advisor

Robert Hondal

Second Advisor

Jay Silveira

Third Advisor

Jose Madalengoitia

Keywords

Thioredoxin reductase, selenocysteine, cysteine, catalysis, beta turn, hydrogen bonding

Abstract

Thiorexodin reductase (TrxR) plays a major role in maintaining cellular antioxidant homeostasis. Mammalian TrxR (mTrxR) is defined by its rare, penultimate amino acid selenocysteine (Sec), which is essential to enzyme catalysis. However, some forms of TrxR in nature do not utilize Sec. One form of TrxR that does not use Sec is mitochondrial TrxR from C. elegans (CeTrxR2). Despite not possessing a Sec residue, CeTrxR2 maintains similar catalytic activity to mTrxR. It has been hypothesized that these Cys-containing TrxRs must somehow activate their active site C-terminal vicinal disulfide bond to achieve catalytic activity comparable to Sec-containing TrxRs, which instead contain a C-terminal vicinal selenosulfide bond. In order to further the understanding of how Cys-containing TrxRs maintain catalytic activity without the presence of Sec, we studied the mechanism of CeTrxR2 by synthesizing a mutant peptide substrate, whose activity towards a truncated form of CeTrxR2 was measured and compared with the wild-type peptide substrate. Our results provide evidence that a crucial hydrogen bond in the enzyme active site induces type VIa beta-turn formation, which places amino acid residues in the correct position for catalysis.

Creative Commons License

Creative Commons Attribution-Noncommercial-No Derivative Works 3.0 License
This work is licensed under a Creative Commons Attribution-Noncommercial-No Derivative Works 3.0 License.

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