Novel Moraceae lectins and their interactions with intestinal and lymphoid cell surfaces
The aims of this study were to screen an array of plant families for novel lectins, to isolate candidate lectins whose reactivity suggested may be functionally useful and to assess the reactivity and modulatory effects of the novel lectins on the cells of the gastrointestinal tract (including the immune regions) and lymphocytes. Few of the seed and bulb samples screened had significant levels of lectin. However, the seeds, roots, stem and bark of Morus nigra, the black mulberry tree from the Moraceae plant family, were found to contain particularly high lectin activity. Two new lectins Morus nigra agglutinin-I (MNAI) and Morus nigra agglutinin-II (MNAII) were isolated. They were found to differ significantly from each other in their sugar specificity, subunit structure, amino acid sequence identity, glycosylation and haemagglutinating activity. MNAI has similarities in sugar inhibition characteristics (GalNAc) and amino acid identity to both MPA and jacalin, which also belong to the Moraceae family. MNAI recognises the similar intestinal glycan structures as jacalin and recognises T/Tn blood group antigen, both with and without sialylation. However, it differs significantly from MPA and jacalin in its lymphocyte stimulatory properties. MNAII appears to be novel and did not show amino acid sequence identity with any known proteins contained in the deltamass database. It is inhibitable by α-D-methyl mannoside. It may have an affinity for structures such as some form of N-linked glycans and appears to have low affinity for α2,6 sialylated structures. It labelled glycan structures present on the villus brush border, dome FAE and most M cells of many of the species tested in vitro.