Human Milk Oligosaccharides as Essential Tools for Basic and Application Studies on Galectins

It is now recognized that human milk oligosaccharides (HMOs) can function both as prebiotics and as decoy receptors that inhibit the attachment of pathogenic microorganisms to the colonic mucosa. They can also act as immune modulators and as colonic maturation stimulators in breast-fed infants. These functions could be mediated by biological interaction between a variety of HMOs and lectins including galectins, selectins and siglecs. There are more than 100 HMOs; they have structural units such as H type 1: Fuc alpha 1-2Gal beta 1-3GlcNAc, Lewis a: Gal beta 1-3(Fuc alpha 1-4) GlcNAc, Lewis b: Fuc alpha 1-2Gal beta 1-3(Fuc alpha 1-4) GlcNAc, Lewis x: Gal beta 1-4(Fuc alpha 1-3) GlcNAc, sialyl Lewis a: Neu5Ac alpha 2-3Gal beta 1-3(Fuc alpha 1-4) GlcNAc, and sialyl Lewis x: Neu5Ac alpha 2-3Gal beta 1-4(Fuc alpha 1-3) GlcNAc. It can be expected that these units may be utilized as tools for studies on the sugar-binding specificities of lectins including galectins, monoclonal antibodies, virus capsid proteins and bacterial toxins. This mini-review presents the dataset of comprehensive HMO structures, including recently clarified ones, in tabular form, for its utilization in such studies, including those of carbohydrate-binding specificity of galectins. In addition, this review introduces recent in vivo and clinical studies, which may be relevant to the biological functions and future utilization of HMOs.