Serum Protein N-Glycans in Colostrum and Mature Milk of Chinese Mothers

Abstract

To study the Chinese human milk N-glycome over lactation, N-glycans were released and separated from serum proteins, purified by solid-phase extraction, and analyzed by matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-TOF-MS). In total, 66 different putative N-glycans were found in the colostrum (week 1) and mature milk (week 4) of seven Chinese mothers. A clear difference was observed between milk of five secretor and two nonsecretor mothers, based on the type and relative amounts of the individual N-glycans. The relative levels of the total neutral nonfucosylated and the fucosylated N-glycans in milk of five secretor mothers increased and decreased over lactation, respectively. This pattern could not be observed for the milk from the two nonsecretor mothers. Overall, this was the first study that provided detailed information on individual N-glycans in milk among mothers and over time as well as that fucosylation of N-glycans in milk was associated with the mother’s secretor status.

Variations in Oligosaccharides and N/O-Glycans in Human Milk through the Eight-Month Lactation Period

“…As shown in Table S4, 23 N -glycans all share a common core sequence, Manα1–3­(Manα1–6)­Manβ1–4GlcNAcβ1–4GlcNAcβ1-Asn-X-Ser/Thr, and could be classified into three types: oligomannose, in which only Man residues extend the core (H5N2, H6N2); complex, in which “antennae” initiated by GlcNAc extend the core (H3N4, H3N5, H5N4-1/3, H3N5F1, H5N4F1-1/2/3, H5N4F1A1-1/2); hybrid, in which one branch of the core was extended by Man and another was extended by one or two GlcNAcs (H3N3F1, H4N3-1/2, H4N3F1-1/2/3, H4N3A1, H5N4-2, H4N3F1A1-1/2/3) . Besides, it was found that the amount of neutral N -glycans (17) in human milk was greater than that of acidic N -glycans (6); similarly, the amount of fucosylated N -glycans (9) in human milk exceeded that of sialylated N -glycans (6), consistent with previous studies. ,, The extracted ion chromatogram and the peak area of each N -glycan derivative are shown in Figure S2 and Table S4, respectively, and the peak area was used for quantitative comparison. The level of total N -glycans was highest at day 7 and fell abruptly at day 15 and month 1, which is consistent with the findings of Bai et al The content of N -glycans at day 15 was similar to that at month 1, month 7, and month 8, which were less than that at month 2 to month 6 (Figure ).…”

“…57 Besides, it was found that the amount of neutral Nglycans (17) in human milk was greater than that of acidic Nglycans (6); similarly, the amount of fucosylated N-glycans (9) in human milk exceeded that of sialylated N-glycans (6), consistent with previous studies. 32,37,58 The extracted ion chromatogram and the peak area of each N-glycan derivative are shown in Figure S2 and Table S4, respectively, and the peak area was used for quantitative comparison. The level of total N-glycans was highest at day 7 and fell abruptly at day 15 and month 1, which is consistent with the findings of Bai et al 31 The content of N-glycans at day 15 was similar to that at month 1, month 7, and month 8, which were less than that at month 2 to month 6 (Figure 4).…”

Glycoproteomics Analysis Reveals Differential Expression of Site-Specific Glycosylation in Human Milk Whey during Lactation

“…Yang et al 23 applied a similar method to compare N-glycosylation in milk fat globule membranes across species, and found that N-glycoproteins in humans were less similar to each other than those in other species. Elwakiel et al 26 used MALDI-TOF-MS to analyze the N-glycans enzymatically released from the glycoproteins in colostrum and mature milk from seven Chinese mothers and identified 66 N-glycans in colostrum and mature milk from seven Chinese mothers. It should be noted that the analysis of the deglycosylated peptides or released glycans cannot reveal the glycoform variation on particular glycosites.…”

Preterm birth and human milk proteome: are we ready for individualized fortification?

“…Besides the distinct amount and composition of proteins and endogenous peptides in preterm milk, significant technological advances have been achieved concerning posttranslational modifications (PTMs) [56]. PTMs are vital to protein structure, stability, function, and health of the intestinal mucosa [57], which might be critical for the usage and effects of proteins and peptides ingested by preterm infants.…”