Plant agglutinin protein, molecular model. This example, from the hedge-apple (Maclura pomifera), is known as Maclura pomifera agglutinin (MPA). It is a tetrameric plant seed lectin. Like all agglutinins, it has the ability to cause cells to stick together (agglutinate). Agglutinins have applications in immunology (such as in the study of antibodies) and in analysis to isolate specific substances that bind to the agglutinin.