Mapping of the N-linked glycoproteome of human spermatozoa.

N-Linked glycosylation, a type of post-translational modification, plays important roles in cell-cell recognition, adhesion, and interactions. Although N-linked glycosylated proteins in sperm are known to be important for gamete binding, little is known about the composition of these proteins, particularly glycosylation sites, in humans. In the present study, the use of glyco-FASP, coupled with the tandem mass spectrometry (MS/MS) method, led to the identification of 554 N-glycosylation sites and 297 N-glycosylated proteins in human sperm. Bioinformatics analysis revealed enrichment of proteins with functions in cell recognition and fertilization. Overall, about 91% of the human sperm N-glycosylated proteins were classified into "membrane", "extracellular region", and "lysosome" groups, based on subcellular localization annotation. Furthermore, glutathione peroxidase 4 (GPX4), a membrane glycoprotein identified in our glycoproteome, was shown to play a significant role in gamete interactions using the in vitro fertilization assay. Accordingly, we propose that characterization of the human sperm glycoproteome should effectively aid in clarifying the mechanisms of fertilization and provide a valuable resource for the future development of male contraceptives and diagnosis of male infertility.