Identification of a specific sperm nuclei selenoenzyme necessary for protamine thiol cross‐linking during sperm maturation

Abstract

A 34 kD selenoprotein purified from rat testis was identified as a specific sperm nuclei glutathione peroxidase (snGPx) with similar properties to phospholipid hydroperoxide glutathione peroxidase (PHGPx). The determination of its primary structure by analysis of its first N‐terminal amino acids, database search, polymerase chain reaction, and sequencing of the cDNA showed that it differs from PHGPx in its N‐terminal sequence. This sequence, which is encoded for by an alternative exon in the first intron of the PHGPx gene, shows more than 50% homology to the protamine sequences and contains a nuclear localization signal. In rats, snGPx is highly expressed in the nuclei of the late spermatids where it is the only selenoprotein present. Its appearance coincides with the reorganization of DNA, which leads to highly condensed chromatin stabilized by cross‐linked protamine thiols. In selenium‐depleted rats where the concentration of snGPx had decreased to one‐third of the normal level, chromatin condensation was severely disturbed. We provided evidence that snGPx acts as a protamine thiol peroxidase responsible for disulfide cross‐linking by reduction of reactive oxygen species. Its dual function in chromatin condensation and the protection of sperm DNA against oxidation is necessary to ensure male fertility and sperm quality.

Molecular biology of glutathione peroxidase 4: from genomic structure to developmental expression and neural function

“…This alternative exon ( Figure 1) encodes for an Arg-rich nuclear insertion sequence, which is retained with the protein even after nuclear import (Pfeifer et al, 2001). This isoenzyme has an apparent molecular mass of approximately 34 kDa and is specifically expressed in late spermatocytes, but was not detected in most other cells and tissues.…”

Distinct Promoters Determine Alternative Transcription of gpx-4 into Phospholipid-Hydroperoxide Glutathione Peroxidase Variants

“…1). This phenomenon was first explained as resulting from alternative pre-mRNA splicing by Pfeifer et al (24). The concept of splicing was also followed through by others (28).…”

“…More recently a selenoprotein band of 34 kDa, detected in testis (23), has been identified as a PHGPx variant with an N-terminal extension that comprises a nuclear targeting signal (24). This sperm nuclei, PHGPx ("sn GPx" in Ref.…”

“…This sperm nuclei, PHGPx ("sn GPx" in Ref. 24), is proposed to be involved in chromatin condensation and thereby to determine the differentiation of spermatogenic cells into spermatozoa (24).…”

New insights into the physiological actions of selenoproteins from genetically modified mice

“…Hence it seems as if Gpx4 is a prototype anti-oxidant enzyme. Yet other data indicated that a sperm cell nuclei-specific nPH-Gpx plays a role in sperm condensation (14,15). Subsequent targeted deletion of this isoform led to delayed chromatin condensation, but surprisingly did not affect male fertility (16).…”