Approaching the protein bound glycome from human breast milk

Apart from being the perfect nutrient human breast milk also confers vital protection from pathogens to the infant. The protective functions are mediated by a number of proteins but also by free oligosaccharides present in human milk. Free oligosaccharides, the third largest fraction in human breast milk, have already been identified and characterized as crucial factors in the protection from pathogens. The role of protein bound glycans, however, has hardly been addressed in this context. Recently Perrier et al. showed that the N-glycans of the "secretory component", an important glycoprotein from human breast milk, are directly engaged in the antipathogenicity against enteropathogenic E. coli and also protect cells against the C. difficile toxin A. Hence protein bound oligosaccharides appear to be more than mere "sweet decoration" of their protein carrier. In order to elucidate the biological function of protein bound oligosaccharides detailed information on their structure is mandatory as the specific composition and the particular linkages of the various monosaccharides within an oligosaccharide are crucial for its biological function. Therefore the comprehensive characterization of all protein bound glycans in human breast milk - as will be undertaken in the course of this project - will provide fundamental knowledge for the understanding of the biological mechanisms and antipathogenic functions. Due to already known changes in composition and specific functions of human breast milk within the course of the first months after birth the protein bound glycome will also be assessed at different stages throughout the lactation period. As hitherto only glycosylation data of few selected glycoproteins are available but no unambiguous glycomic investigation regarding the entity of human breast milk glycoproteins has been performed a combination of novel purification strategies and already established analytical methods will allow an unbiased and detailed characterization of the complex protein bound glycome present in human breast milk for the first time. The eventual results of the project will significantly contribute to the understanding and exploration of the biological function of breast milk - in particular its role in the protection from pathogens.