Probable receptor which is required for the oocyte-to-zygote transition although its exact function is controversial (By similarity). Seems to be required for fertilization probably by promoting the interaction or fusion between sperm and oocyte (PubMed:16360684). Conversely, shown to be dispensable for fertilization but required for the formation of a continuous and cohesive eggshell chitin layer by maintaining a homogenous distribution of chitin synthase chs-1 at the unfertilized oocyte cell membrane (By similarity). Appears to recruit or maintain together to the unfertilized oocyte cortex several proteins including chs-1, kinase mbk-2 and pseudophosphatases egg-3, and possibly egg-4 (By similarity). Localizes to the cell membrane of developing oocytes. Plasma membrane localization requires extracellular matrix protein cbd-1. After fertilization, localizes to endosomes in zygotes. RNAi-mediated knockdown results in sterility due to the loss of oocyte fertilization.