Probable receptor which is required for the oocyte-to-zygote transition although its exact function is controversial (PubMed:16360684, PubMed:20971008). Redundantly with egg-1, 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 together with egg-1 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 (PubMed:20971008). Appears to recruit or maintain together to the unfertilized oocyte cortex several proteins including chs-1, kinase mbk-2 and pseudophosphatase egg-3, and possibly egg-4 and egg-5 (PubMed:20971008). Localizes to the cell membrane of developing oocytes (PubMed:20971008). Plasma membrane localization requires extracellular matrix protein cbd-1 (PubMed:20971008). After fertilization, localizes to endosomes in zygotes (By similarity). Severe sterility at the restrictive temperature of 25 degrees Celsius (PubMed:16360684). Accumulation of unfertilized oocytes in the uterus, although this is controversial (PubMed:16360684). Simultaneous RNAi-mediated knockdown with egg-1 results in a fragmented eggshell chitin layer which often accumulates at one end of the embryo (PubMed:20971008). In unfertilized oocytes, disrupts the homogenous distribution of cortical chitin synthase chs-1, pseudophosphatase egg-3 and kinase mbk-2 (PubMed:20971008). In a egg-1 (tm1071) mutant background, causes polyspermy (PubMed:20971008).