Composed of four subunits of approximately equal size, soybean agglutinin is a family of closely related isolectins. This glycoprotein has a molecular weight of about 120 kDa and an isoelectric point near pH 6.0. SBA preferentially binds to oligosaccharide structures with terminal α- or β-linked N-acetylgalactosamine, and to a lesser extent, galactose residues. Binding can be blocked by substitutions on penultimate sugars, such as fucose attached to the penultimate galactose in blood group B substance.
An important application for SBA is the separation of pluripotent stem cells from human bone marrow. Cells fractionated by SBA do not produce graft vs host disease and can be used in bone marrow transplantation across histocompatibility barriers.