Exploring boar sperm sialylation during capacitation using boronic acid-functionalized beads

Sialic acid (SA), which usually occupies the terminal position of oligosaccharide chains in mammalian spermatozoa, has important functions in fertilization. Compared with other methods, such as lectin probing, boronic acid could recognize and bind SA with a higher affinity and specificity at pH 6.9. In this study, two boronic acid carriers, 3-aminophenylboronic acid-labeled fluorescent latex (CML-APBA) and magnetic beads (CMM-APBA were applied to explore surface sialylation profile and sialoglycoproteins of the boar sperm. There are three binding sections of CML-APBA on the head of ejaculated sperm: acrosomal region, equatorial segment and the head posterior, which are the major regions undergoing sialylation. After capacitation in vitro, two major binding patterns of CML-APBA exists on sperm head. On some spermatozoa, sialylation exists on the equatorial segment and the posterior head, whilst on other spermatozoa, sialylation occurs on the acrosomal region and equatorial segment. Flow cytometry analysis suggested that the level of sialylation on boar sperm membrane decreases after capacitation. Furthermore, using CMM-APBA, we pulled down sialylated proteins from spermatozoa. Among them, two decapacitation factors associating on sperm surface, AWN and PSP-1, were identified. The levels of the two proteins reduced during capacitation, which might contribute to the decrease of sialylation on boar sperm surface.