Jacalin is a lectin composed of four subunits of approximately 16 kDa each. This lectin appears to bind only O-glycosidically linked oligosaccharides, preferring the structure galactosyl (β-1,3) N-acetylgalactosamine. This structure (the T-antigen) is the oligosaccharide to which peanut agglutinin (PNA) binds. However, unlike PNA, Jacalin will bind a mono- or disialylated form of this structure. This lectin has been used to purify human IgA. The specificity of this lectin also affords the opportunity to localize or isolate glycoproteins with O-glycosidically linked oligosaccharide side chains.