Fruit-specific lectins from banana and plantain

One of the predominant proteins in the pulp of ripe bananas (Musa acuminata L.) and plantains (Musa spp.) has been identified as a lectin. The banana and plantain agglutinins (called BanLec and PlanLec, respectively) were pur ified in reasonable quantities using a novel isolation procedure, which pre vented adsorption of the lectins onto insoluble endogenous polysaccharides. Both BanLec and PlanLec are dimeric proteins composed of two identical sub units of 15 kDa. They readily agglutinate rabbit erythrocytes and exhibit s pecificity towards mannose. Molecular cloning revealed that BanLec has sequ ence similarity to previously described lectins of the family of jacalin-re lated lectins, and according to molecular modelling studies has the same ov erall fold and three-dimensional structure. The identification of BanLec an d PlanLec demonstrates the occurrence of jacalin-related lectins in monocot species, suggesting that these lectins are more wide-spread among higher p lants than is actually believed. The banana and plantain lectins are also t he first documented examples of jacalin-related lectins, which are abundant ly present in the pulp of mature fruits but are apparently absent from othe r tissues. However, after treatment of intact plants with methyl jasmonate, BanLec is also clearly induced in leaves. The banana lectin is a powerful murine T-cell mitogen. The relevance of the mitogenicity of the banana lect in is discussed in terms of both the physiological role of the lectin and t he impact on food safety.