Protein Disulfide Bond Formation in the Reducing Environment of Cytoplasm

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ABSTRACT Nearly every cellular process is controlled by thiol-based redox regulation. However, the mechanisms of targeted cysteine oxidation in the reducing environments of cytosol, mitochondria, and nucleus remain unclear. Hydrogen peroxide (H2O2) is known to induce oxidation of cysteines in proteins, but the precise physiological mechanisms are not fully understood. This mild cellular oxidant is metabolized by six mammalian peroxiredoxins (Prxs) as well as several glutathione peroxidases and catalases. Prxs are expressed in a cell type- or tissue-specific manner, and their reduced forms are regenerated by thioredoxin, other thiol oxidoreductases, or glutathione. Previous studies indicate that Prxs can directly interact with regulatory proteins and participate in cellular signaling. Recently, the endoplasmic reticulum specific PrxIV (erPrxIV) was shown to function in the pathway of disulfide bond formation by oxidizing cysteines in protein disulfide isomerase, which further oxidized client proteins in the endoplasmic reticulum; together protein disulfide isomerase and erPrxIV formed disulfides in cellular proteins. We identified a new form of the disulfide forming PrxIV, cPrxIV, located in the cytosol. In preliminary studies, we found that cPrxIV is highly expressed in elongating spermatids in testes and is conserved in placental mammals. We further characterized the properties and expression patterns of this protein and generated a knockout mouse model to study the physiological function of cPrxIV. By analogy to the endoplasmic reticulum form of this protein, we hypothesize that cPrxIV catalyzes disulfide bond formation in the cytosol and this function is particularly important during spermatogenesis. We propose to characterize cPrxIV and its role in disulfide bond formation and redox homeostasis. Specifically, we intend to (i) determine if cPrxIV participates in disulfide bond formation in vitro and in vivo; (ii) identify interacting client partners and a reductase for cPrxIV; and (iii) characterize the redox metabolome of PrxIV KO mice.