Lectin that recognizes O-linked galactose-beta-1,3-N-acetylgalactosamine, a disaccharide (Thomsen-Friedenreich antigen or T-disaccharide), present on cell surface glycoproteins. Can also bind galactose-beta-1,3-N-acetylglucosamine. Does not bind monosaccharides. Can be internalized by clathrin-coated vesicles after binding to surface glycoproteins. After internalization it inhibits nuclear import of nuclear localization signal dependent proteins. Inhibits proliferation of malignant cells without cytotoxicity for normal cells. Homotetramer. Lectins can be used to recognize and purifiy specific glycoproteins, and for the purification of cells with specific surface glycoproteins. Has potential as anti-proliferative agent. Sold under the name lectin from Agaricus bisporus by Sigma-Aldrich and under the name of Agaricus bisporus (Mushroom) agglutinin (ABA) by USBiological. Each monomer has 2 distinct carbohydrate binding sites, one for galactose-beta-1,3-N-acetylgalactosamine and another for galactose-beta-1,3-N-acetylglucosamine. Belongs to the fungal fruit body lectin family. Frameshift correction allows the C-terminal sequence to be compatible with the results of mass spectrometry and X-ray crystallography.