This is the C-terminal domain found in Cucumaria echinata CEL-III protein which is a lectin that exhibits both hemolytic and hemagglutinating activity. The domain is responsible for oligomerization and insertion of CEL-III into the erythrocyte membrane. The domain is composed of eight stranded beta sandwich and two alpha helices, the latter changes conformation upon binding to the cell surface carbohydrates [1].

1: Crystal structure of the hemolytic lectin CEL-III isolated from the marine invertebrate Cucumaria echinata: implications of domain structure for its membrane pore-formation mechanism. Uchida T, Yamasaki T, Eto S, Sugawara H, Kurisu G, Nakagawa A, Kusunoki M, Hatakeyama T; J Biol Chem. 2004;279:37133-37141. PMID:15194688