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.
Cy3 can be used to visualize the binding pattern of Maclura pomifera Lectin (MPL/MPA) in cellular imaging and flow cytometry. Cy3 is more photostable than many other fluorophores and can be seen with TRITC filter sets. It is commonly combined with green-fluorescent dyes for dual-labeling.