Alpha 2,3- and alpha 2,6-sialylation of human skim milk glycoproteins during milk maturation

Abstract

Human milk is a source of glycoconjugates, sialylated forms of which enrich the newborn immature immune system and are crucial for their proper development and well-being. Here, we analyzed the expression of α2,3-/α2,6-sialylated glycotopes on skim milk glycoproteins over lactation. Milk samples were analyzed by lectin-blotting using α2,3- and α2,6- sialic acid specific Maackia amurensis (MAA) and Sambucus nigra (SNA) lectins and sialyl- and asialyl-T antigen specific Artocarpus integrifolia (Jacalin) and Arachis hypogaea (PNA) lectins. The reactivities of MAA, SNA, Jacalin and PNA with milk glycoproteins showed that they are heavily decorated with α2,3-/α2,6-linked sialic acid and sialyl-T antigen and to a lesser degree with asialyl-T antigen. Despite individual differences of particular glycoproteins, a sharp and significant decline of α2,6-sialylated glycotopes and sialyl-T antigens and a weaker but significant decrease of α2,3-sialylated glycotopes and asialyl-T antigens on milk glycoproteins during milk maturation was observed. The expression of α2,3-/α2,6-sialylated glycotopes, sialyl- and asialyl-T antigens corresponds to milk maturation but differs in relation to the analyzed glycoprotein. Sialylated milk glycoproteins are considered as a part of innate immunity provided to neonates. Further investigations are needed to understand if they may be useful in milk banking to control the biochemical quality of milk.