Identification and Characterization of Alternatively Transcribed Form of Peroxiredoxin IV Gene That Is Specifically Expressed in Spermatids of Postpubertal Mouse Testisстатья
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Аннотация:2-cysteine (Cys) peroxiredoxins (Prxs), which include mammalian Prx I to IV, possess two conserved Cys residues that are readily oxidized by H2O2 to form a disulfide. In the case of Prx I to III, the disulfide is reduced by thioredoxin, thus enabling these proteins to function as peroxidases. Prx IV was previously shown to be synthesized as a 31-kDa polypeptide with an NH2-terminal signal peptide that is subsequently cleaved to generate a 27-kDa form of the protein that is localized to the endoplasmic reticulum. A form of Prx IV larger than 27-kDa revealed by immunoblot analysis was suggested to represent the unprocessed, 31-kDa form, but this larger form was detected only in spermatids of the post pubertal testis. We now show that the larger form of Prx IV (here designated Prx IV-L) detected in the testis is actually a product of alternative transcription of the Prx IV gene that is encoded by a newly identified exon 1A together with exons 2 to 7 that are shared with the 27-kDa form (designated Prx IV-S). Prx IV-L was detected in spermatids but not in mature sperm, it was found to exist mostly as a disulfide-linked dimer in the testis, and it appears not to function as a peroxidase. Phylogenetic analysis showed that the Prx IV-S gene is present in all vertebrates examined, whereas the Prx IV-L gene was detected only in placental mammals. We suggest that Prx IV-L functions as an H2O2 sensor that mediates protein thiol oxidation required for the maturation of spermatozoa in placental mammals.