CARBOHYDRATE-BINDING ACTIVITY IN HUMAN SPERMATOZOA - LOCALIZATION, SPECIFICITY, AND INVOLVEMENT IN SPERM-EGG FUSION

Sperm carbohydrate binding activity is involved in gamete recognition, We identified a human sperm protein extracted under reducing conditio ns, and with a molecular mass of 65 kDa on sodium dodecyl sulphate-pol yacrylamide gel electrophoresis (SDS-PAGE), and which binds D-mannose coupled to albumin (DMA) in presence of cations and a neutral pH. Epif luorescence microscopy showed that fluorescein-DMA binds to dead or pe rmeabilized sperm heads, The DMA-binding activity of human sperm heads was highly specific for a polysaccharide structure containing charged sugar residues, After capacitation, or induction of the acrosome reac tion using solubilized zonae pellucidae, fluorescein-DMA was bound res pectively to 10.3% (+/- 3.5%) and to 37.6% (+/- 2.1%) of viable sperm heads, The sequential analysis of viable spermatozoa for fluorescein-D MA binding and for rhodamine-Pisum sativum agglutinin binding, showed that DMA-binding sites are present in viable acrosome-reacted spermato zoa. Three dimensional analysis of fluorescence and ultrastructural st udies showed that DMA-binding sites are mostly restricted to the sub-a crosomal space of the equatorial segment, Incubation of spermatozoa an d zona-free hamster eggs in the presence of DMA was associated with a dose-dependent significant reduction in the number of spermatozoa boun d to the oolemma, compared with a control, and to a dose-dependent inh ibition of oocyte penetration, This effect was highly specific for DMA , suggesting that DMA-binding sites in human spermatozoa are involved in sperm-egg fusion.