Co-localization of receptor and transducer proteins in the glycosphingolipid-enriched, low density, detergent-insoluble membrane fraction of sea urchin sperm

The low density, detergent-insoluble membrane fraction (LD-DIM), where gang liosides are likely to be highly enriched, was prepared from sperm of two s ea urchin species, Hemicentrotus pulcherrimus and Strongylocentrotus porpur atus. Immunoblotting showed the presence in the LD-DIM of two receptors for egg ligands, a glycosylphosphatidylinositol (GPI)-anchored protein, and fo ur proteins which may be involved in signal transduction. Co-immunoprecipit ation revealed that at least three proteins, the speract receptor, the 63kD a GPI-anchored protein and the alpha subunit of a heterotrimeric Gs protein , are localized in the LD-DIM. This suggests that the LD-DIM fraction may b e a membrane microdomain for speract-speract receptor interaction, as well as the subsequent signal transduction pathway involved in induction of sper m respiration, motility and possibly the acrosome reaction.