Bovine colostrum, transitional and mature milk alpha-lactalbumin N-glycosylation

ABSTRACT: α-Lactalbumin is an abundant protein present in the milk of most mammals, and is associated with biological, nutritional and technological functionality. Its sequence presents N-glycosylation motifs, the occupancy of which is species-specific, ranging from no to full occupancy. Here, we investigated the N-glycosylation of bovine α-lactalbumin in colostrum and milk sampled from four individual cows, each at 9 time points starting from the day of calving up to one month post-partum. Using a glycopeptide-centric mass spectrometry-based glycoproteomics approach, we identified N-glycosylation at both Asn residues found in the canonical Asn-Xxx-Ser/Thr motif, i.e., Asn45 and Asn74 of the secreted protein. We found similar glycan profiles in all four cows, with partial site occupancies averaging at 35% and 4% for Asn45 and Asn74, respectively. No substantial changes in occupancy occurred over lactation at either site. Fucosylation, sialylation primarily with N-acetylneuraminic acid (NeuAc) and a high ratio of N,N'-diacetyllactosamine (LacdiNAc)/N-acetyllactosamine (LacNAc) antennae were characteristic biochemical features of the identified N-glycans. While no substantial changes occurred in site occupancy at either site during lactation, the glycoproteoform profile revealed lactational dynamics; the maturation of the α-lactalbumin glycoproteoform repertoire from colostrum to mature milk was marked by substantial increases in neutral glycans and the number of LacNAc antennae per glycan, at the expense of LacdiNAc antennae. While the implications of α-lactalbumin N-glycosylation on functionality are still unclear, we speculate that N-glycosylation at Asn74 results in a structurally and functionally different protein, due to competition with the formation of its two intra-molecular disulphide bridges.

INSTRUMENT(S): Orbitrap Fusion Lumos

ORGANISM(S): Bos Taurus (bovine)

TISSUE(S): Milk

SUBMITTER: Inge Gazi  

LAB HEAD: Albert J. R. Heck

PROVIDER: PXD050331 | Pride | 2024-08-09

REPOSITORIES: Pride