Binds negatively charged membrane lipids, such as phosphatidylserine and phosphoinositides. May play a role in cell-cell adhesion processes in the retina, via homomeric interaction between octamers present on the surface of two neighboring cells. Required for normal structure and function of the retina (By similarity). Homooctamer of 4 homodimers; disulfide-linked. The homooctamer has a flat, cogwheel structure with a diameter of about 14 nm. Two stacked octamers can assemble to form a hexadecamer. Binds to phosphatidylserine-containing lipid membranes and embeds itself partially into the lipid bilayer. Lipid-binding requires the presence of Ca(2+) ions.