Peanut agglutinin, a lectin with an unusual quaternary structure and interesting ligand binding properties

Lectins are multivalent proteins which play their biological role through the ability to specifically bind different carbohydrate structures. This ability has also led to their myriad applications. They occur in all forms of life. Among plant lectins, those from leguminous plants constitute the most thoroughly studied family. Most of the well-characterized legume lectins can be classified as mannose (Man)/glucose (Glc) specific or galactose (Gal)/N-acetylgalactosamine (GalNAc) specific. Tetrameric, non-glycosylated peanut agglutinin (PNA) is the most thoroughly investigated member of the Gal/GalNAc specific family of legume lectins. Its structure indicated that open quaternary association also needed to be considered when dealing with multimeric proteins. The structure also helped to establish legume lectins as a family of proteins in which small alterations in essentially the same tertiary structure lead to large changes in quaternary association. It provides an explanation for the exclusive specificity ...