Integrated Roles of The Thioredoxin-related Protein of 14 kDa, TRP14, in Sulfur Amino Acid Metabolism, Protein Posttranslational Modifications and Signaling.

Thioredoxins and glutaredoxins are typically small "redoxin" proteins that play predominant roles in shuttling reducing power from the primary nicotinamide adenine dinucleotide phosphate (NADPH)-dependent disulfide reductases, thioredoxin reductase (TrxR, TXNRD) and glutathione disulfide-reductase (Gsr) to diverse downstream substrates. Cells can have dozens to hundreds of redoxin proteins, which in combination will reduce a vast array of substrates, including proteins, metabolites, and others. Whereas there is considerable overlap between different redoxins and their preferred substrates, the thioredoxin-related protein of 14 kDa, TRP14 (also named TXNDC17), has unique characteristics that support its critical roles in cysteine acquisition and mediation of redox-regulation in cellular signaling. TRP14 is particularly efficient at cystine reduction and at modulating protein nitrosylation, cysteinylation, and persulfidation, yet it does not effectively reduce many common redoxin substrates including redox enzymes and oxidative stress-induced protein-disulfides. We propose that this functional specialization allows TRP14 to support its essential roles in cysteine acquisition and signaling under both normal and oxidative stress conditions, in the latter case, wherein other redoxins likely become overwhelmed resolving oxidative stress. Specialized attributes of TRP14 are reviewed and discussed here.