A 140-kDa glycopeptide from the sperm ligand of the vitelline coat of the freshwater bivalve Unio elongatulus, only contains O-linked oligosaccharidechains and mediates sperm-egg interaction

In previous studies we found that sperm binding activity in the vitelline c oat of the freshwater bivalve Unio elongatulus is located on the O-linked o ligosaccharide chains of gp273, one of the two major components of the extr acellular coat, and that fucose plays a key role in this interaction. In th is paper we report the partial characterization of a large glycopeptide (ab out 140 kDa) obtained by cyanogen bromide fragmentation of gp273, that main tains sperm binding activity. Lectin blotting revealed that the glycopeptid e reacted with lectins from Arachis hypogaea (PNA) and Lotus tetragonolobus (LTA) but not Canavalia ensiformis (ConA). No other PNA-positive fragments could be detected in the electrophoretic pattern of fragmented gp273 but s everal ConA-positive fragments of lower molecular weight were present indic ating that all the O-linked chains are clustered together in this fragment. Two-dimensional gel electrophoresis of the fragment revealed it to be acid ic in nature in contrast with the neutral character of the whole gp273 mole cule. Competition binding assay showed that this fragment is a strong inhib itor of the interaction, whereas no effect was detected using the ConA-posi tive peptides. This confirms that the sperm receptor activity of gp273 is r elated to its O-linked chains. The immunodominance of this fragment is also discussed. (C) 1999 Wiley-Liss, Inc.