Characterisation of Morus nigra agglutinins I and II, and their biological activity in the mammalian intestine
Two novel lectins were purified from the Moraceae plant Morus nigra or Black Mulberry. These lectins were named Morus nigra agglutinin I (MNA I) and Morus nigra agglutinin II (MNA II). Data obtained from carbohydrate inhibition studies indicated that MNA I specifically bound N-acetylgalactosamine and D-galactose, and in contrast, MNA II selectivity bound α-methyl-D-mannoside and D-mannose. MNA I is composed of two glycosylated α-chains and two β-chains, both of which share a high degree of amino acid sequence identity with the N-terminal regions of the α- and β-chains of the Moraceae lectins, Jacalin and Macluar pomifera agglutinin (MPA). MNA II consists of three dominant subunits, each of which has the same N-terminal amino acid sequence. This sequence shares a degree of N-terminal amino acid sequence identity with the Moraceae D-mannose binding lectin KM+ and the β-chains of Jacalin, MPA and MNA I. Glycosylation of the MNA II subunits was not detected. The binding characteristics of Moraceae lectins to the intestinal brush border were assessed using both in vitro and in vivo approaches. Initially in vitro studies using Brush Border Vesicle preparations were conducted. Thereafter in situ experiments using rat intestinal ligated loops were carried out. The in vitro and in situ binding studies showed that MNA I had a low binding capacity for the rat intestinal brush border, however Western blot studies illustrated that MNA I selectively bound to two rat intestinal brush boarder proteins. Initial in vitro data indicated that MNA II also had a low binding capacity for the rat intestinal brush border. However, additional in vitro and in situ studies showed MNA II bound extensively to the jejunal villi. Furthermore, considerable MNA II uptake into the jejunal enterocytes and lamina propria was detected.