Role of egg sulfolipidimmobilizing protein 1 on mouse sperm-egg plasma membrane binding

We have shown that sperm sulfolipidimmobilizing protein 1 (SLIP1, molecular mass of 68 kDa), a sulfogalactosylglycerolipid (SGG)-binding protein, is s ignificant in sperm-zona pellucida (ZP) interaction. The objective of this study was to localize SLIP1 on the egg and determine its role in gamete int eraction. Immunofluorescence and immunoprotein A gold electron microscopy l ocalized SLIP1 to the egg plasma membrane. In vitro gamete binding, using z ona-free eggs preincubated with antiSLIP1 Fab before coincubation with sper m, showed a significant, dose-dependent decrease in sperm-egg plasma membra ne binding. Similar results were obtained when affinity-purified antiSLIP1 IgG was used for egg pretreatment. The significance of egg SLIP1 in sperm-e gg plasma membrane binding was further demonstrated by a decrease (36-52%) in in vitro fertilization when zona-intact eggs were pretreated with antiSL IP1 IgG. Since SLIP1 has been shown to bind SGG in vitro, we investigated t he possibility that sperm SGC may participate in sperm-egg plasma membrane binding through egg SLIP1. Pretreatment of sperm with antiSGG Fab prior to coincubation with zona-free eggs resulted in a dose-dependent decrease in s perm-egg plasma membrane binding. Collectively, these findings strongly sug gest a role for egg SLIP1 in sperm-egg plasma membrane interaction, which m ay be through its binding to sperm SGG.