Maclura pomifera agglutinin or lectin (MPA/MPL) is tetrameric plant protein purified by fractionation. MPA has a molecular weight of about 44,000 and consists of four subunits. It has an isoelectric point between pH 4.8 and pH 5.3, and blood group specificity towards A, B, and O (-SA). This lectin has a high affinity for tumor-associated T-antigen disaccharide (Galβ1,3GalNAcα) and many O-linked glycopeptide structures. The structure of Galβ1,3GalNAcα occurs on the surface of tumor cells as a mucin-associated antigenic marker, termed as T-antigen. It is also the central element in O-linked glycopeptide structures on other mammalian glycoproteins.
Maclura pomifera Lectin (MPL/MPA) is conjugated to ferritin, that has a molecular weight of 474,000 g/mol (all 24 subunits combined). Ferritin-conjugated lectins can be used to visualize localization of specific saccharide moieties and examine the distribution of plasma membrane glycoproteins. These conjugates can be viewed via electron microscopy.