Large-scale preparation and glycan characterization of sialylglycopeptide from bovine milk glycomacropeptide and its bifidogenic properties

Abstract

Bovine glycomacropeptide (GMP) is a 7,000-Da glycopolypeptide released from κ-casein during cheese making. The O-glycan chains linked to GMP have many biological activities, but their utilization for nutraceutical products is limited due to their low content. To concentrate the functional glycan chains of GMP, we prepared sialylglycopeptide concentrate (SGC) from GMP-containing whey protein concentrate via proteolytic digestion of peptide chains and concentration of sialylglycopeptide by ultrafiltration using membranes with a molecular weight cut-off of 1,000 Da. The abundant saccharides detected in the prepared SGC were N-acetylneuraminic acid (Neu5Ac: 32.3% wt/wt), N-acetylgalactosamine (11.3%), and galactose (10.2%), which constitute O-glycans attached to GMP. The Neu5Ac content in SGC was found concentrated at approximately 4.8-fold of its content in GMP-containing whey protein concentrate (6.8%). Structural analysis of O-glycopeptides by liquid chromatography tandem mass spectrometry identified 88 O-glycopeptides. Moreover, O-acetylated or O-diacetylated Neu5Ac was detected in addition to the previously characterized O-glycans of GMP. Quantitative analysis of O-glycan in SGC by fluorescence labeling of chemically released O-glycan revealed that a disialylated tetrasaccharide was the most abundant glycan (76.6% of the total O-glycan). We further examined bifidogenic properties of SGC in vitro, which revealed that SGC served as a more potent carbon source than GMP and contributes to the growth-promoting effects on certain species of bifidobacteria. Overall, our study findings indicate that SGC contains abundant O-glycans and has a bifidogenic activity. Moreover, the protocol for the preparation of SGC described herein is relatively simple, providing a high yield of glycan, and can be used for large-scale preparation.