The Bivalve Egg's Lectin Recognizing Sperm Glycosphingolipid

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An acidic glycosphingolipid was isolated from spermatozoa of the fresh-water bivalve, Hyriopsis schlegelii, and it was found to have the following structure: GlcA4Me 1-4[GalNAc3Me 1-3] Guc 1-4GlcNAc 1-2Man 1-3[Xy1 1-2]Man 1-4Glc 1-1Ceramide. This is a unique glycolipid, in that a 4-O-mathylglucuronic acid and an internally located fucose are contained as sugar residues and also thought to exist specifically on the cell surface of the bivalve spermatozoa placed taxonomically in the Veneridae, Unionidae and mytilidae. These intrinsic facts let us explore possible roles for sperm-egg interaction. Then, by affinity coulumn chromatography with the octyl-Sepharose carrying lipid, we tried to extract certain substances that recognize the acidic lipid from a 100,000 x g supernatant of the Hyriopsis egg homogenates. The extract was demonstrated to agglutinate spermatozoa from certain bivalve species, and also the acidic lipid-containing liposomes. On SDSpolyacrylamide gel electrophoresis, the majority of the extract was confirmed to the bands within the five regions of apparent molecular mass: 100K, 80, 60K, 40K, and 20KDa. All of them were found to directly bind to ^3H-labelled acidic lipid, and this indicated that the initial binding activity was found in a production of the 20KDa. When living Mytilus edulis eggs were mixed with sperm preincubated with the extract, it was found to completely inhibit the fertilization.