Quantitative glycopeptide changes in rat sperm during epididymal transit

Mammalian spermatozoa acquire fertilizing potential as they undergo a series of changes during epididymal transit. One major facet of such is the alterations in the sperm glycome. Modifications of the sialic acid content within glycan moieties are known to regulate epitope presentation and cellular adhesion and signaling, all of which may be critical for sperm to successfully reach and fertilize the egg. To date, there is paucity of information regarding the sialic acid changes that occur on spermatozoa during epididymal transit. Therefore, the aim of this study was to identify N-linked sialylated glycoproteins in rat epididymal sperm and investigate whether they are regulated during epididymal transit. Sialylated glycopeptides from caput, corpus, and cauda spermatozoa were enriched using titanium dioxide beads. Bound N-linked glycopeptides were released by enzymatic deglycosylation using PNGase F and then analyzed by liquid chromatography tandem-mass spectrometry. A total of 92 unique N-linked sialylated glycopeptides were identified from 65 different proteins. These included members of the disintegrin and metalloproteinase domain-containing protein family (ADAM), Basigin, and Testis-expressed protein 101 (TEX101). Remarkably, label-free quantification showed that more than half of these peptides (48/92) were regulated during epididymal transit. Of interest, the protein TEX101 exhibited PNGase F-resistant deglycosylation under the conditions used in this study. The results from this study showed that changes in the N-linked sialoglycoprotein profile is a major hallmark of sperm maturation in rats.