N-Glycoproteomics of Human Seminal Plasma Glycoproteins

Abstract

Seminal plasma aids sperm by inhibiting premature capacitation, helping in the intracervical transport and formation of an oviductal sperm reservoir, all of which appear to be important in the fertilization process. Epitopes such as Lewis x and y are known to be present on seminal plasma glycoproteins, which can modulate the maternal immune response. It is suggested by multiple studies that seminal plasma glycoproteins play, largely undiscovered, important roles in the process of fertilization. We have devised a strategy to analyze glycopeptides from a complex, unknown mixture of protease-digested proteins. This analysis provides identification of the glycoproteins, glycosylation sites, glycan compositions, and proposed structures from the original sample. This strategy has been applied to human seminal plasma total glycoproteins. We have elucidated glycan compositions and proposed structures for 243 glycopeptides belonging to 73 N-glycosylation sites on 50 glycoproteins. The majority of the proposed glycan structures were complex type (83%) followed by high-mannose (10%) and then hybrid (7%). Most of the glycoproteins were either sialylated, fucosylated, or both. Many Lewis x/a and y/b epitopes bearing glycans were found, suggesting immune-modulating epitopes on multiple seminal plasma glycoproteins. The study also shows that large scale N-glycosylation mapping is achievable with current techniques and the depth of the analysis is roughly proportional to the prefractionation and complexity of the sample.

Insights into the hyperglycosylation of human chorionic gonadotropin revealed by glycomics analysis

“…Bisected N-glycans terminated with Lewis X antigens are rare in humans. Interestingly, apart from pregnancy hCG described herein, sperm are the only reported human source of Insights into the hyperglycosylation of human chorionic gonadotropin substantial amounts of this family of glycans, which have been implicated in the inhibition of immune responses [50,51]. There have been many models presented to explain how the pregnant human female accommodates the foreign fetus during pregnancy.…”

Could the glycosylation analysis of seminal plasma clusterin become a novel male infertility biomarker?

“…CLU has six possible n ‐glycosylation sites. Saraswat et al (2016) carried out extensive research concerning the presence and structure of human seminal plasma glycoproteins. In the report, the authors showed that CLU had four n ‐glycosylation sites.…”

“…They contained fucose, Lewis x /Lewis a , blood group H, or Lewis y /Lewis b oligosaccharide structures (Figure 1). In some regions of CLU, huge microheterogeneity was observed (Saraswat et al, 2016). We have not found any further data concerning glycans alterations in the seminal plasma CLU of infertile men so far.…”

Occurrence and reproductive roles of hormones in seminal plasma

“…The another study identified two protein biomarkers (ECM1 and TEX101) that can distinguish between non-obstructive and obstructive azoospermia with high sensitivity and specificity [ 124 ]. The latest analytical techniques enable measurement of post-translationally modified proteins – such glycoproteins in human seminal plasma [ 125 ] of which sialylated fibronectin was found to be associated with abnormal sperm parameters [ 126 , 127 ].…”