Macoma birmanica agglutinin recognizes glycoside clusters of beta-GlcNAc/Glc and alpha-Man

Macoma birmanica agglutinin (MBA) that seems to play crucial roles in the innate immunity of marine bivalve, M. birmanica has been earlier defined as GlcNAc/Man specific. However, most complementary carbohydrate structures to its binding domain and ligand clustering in its recognition profile have not been established. In this study, the complete recognition profile of MBA was examined by enzyme-linked lectin-sorbent assay and inhibition assay. Among the monosaccharides tested, GlcNAc was more reactive followed by Man and Glc, others were non-reactive; revealing the importance of equatorial -NAc group at C-2, -OH group at C-4 and C-6, and pyranose conformation of hexose. Moreover, beta-glycosides of GlcNAc and Glc were more potent whereas for Man it was alpha-glycoside. MBA recognized both exposed and internal alpha-Man and beta-GlcNAc/Glc residues well with most linkages except (beta1-4). This binding pattern was further extended and confirmed by polyvalent glycoside clusters of GlcNAc(beta1-2)Man(alpha1-, which was a better inhibitor than Man(alpha1-2/3/6)Man(alpha1- or Man(alpha1-3/6)Man(beta1- present in well-defined naturally occurring glycoproteins. This broad range specificity explains the importance of MBA as an important pattern recognition molecule that provides more realistic picture of carbohydrate-based immune response triggering.