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Function
One function of TrxR is to reduce compounds such as H2O2 which This protein's mechanism is greatly related to the orientation of the FAD and NADPH domains. When the NADPH is oriented 66º off of the FAD it allows electrons to transfer from the NADPH to the FAD and through that to the active site of the enzyme and the disulphide that resides there. The disulphide is then reduced to Trx-(SH)2 which is then used as a reducing agent for other compounds such as H2O2. Without the proper orientation of the two domains (FAD and NADPH) the electrons would not travel from NADPH to the FAD thus preventing the reaction completely.
The catalytic site for TrxR is a -Cys-Val-Asn-Val-Gly-Cys- group that is located by the FAD site allowing for the easy transport of the extra electrons to the Thioredoxin present.
A second function of this protein is utilized in the regulation of DNA translation and in apoptosis. A normal stop codon (UGA, UAA, and UAG) stops the translation of the mRNA, but in the presence of TrxR an extra Selenocysteine is added to the end of the protein chain. This extra amino acid is what marks the structure for death inside the cell. Enough of these structures in the cell and the entire cell will undergo apoptosis.
Disease
When left unregulated cell death does not perform as functioned resulting in a build-up of tissue and most often the cause of tumorous growths in the body. This includes cancerous growths as well as non-cancerous.
Relevance
There needs to be be great surveillance on TrxR. Since the enzyme's action works specifically with cell death it needs to be highly regulated. Leaving TrxR unchecked could lead to too little or too much cell death. If TrxR is mutated or inhibited apoptosis is avoided tumors can form
Structural highlights
-Cys-Gly-Pro-Cys- End of Beta-2 strand before alpha-helix
The Cys link in a disulphide and then nearby His causes breaking of disulphide bond in thioredoxin
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