Characterization of sheep milk fat globule proteins by two-dimensional polyacrylamide gel electrophoresis/mass spectrometry and generation of a reference map

Milk fat globules (MFGs) are fat droplets released in milk as vesicles with a tripartite membrane structure. MGF proteins (MFGPs) are involved in many metabolic processes, and are recently gaining growing attention. Sheep MFGPs were extracted and characterized by two-dimensional polyacrylamide gel electrophoresis/mass spectrometry (2-DE/MS), and a reference map was established. Specifically, 29 MFGPs were successfully identified by tandem MS from 61 spots, localized in the reference map, and characterized for gene ontology. For comparison, skim milk and whey were also subjected to 2-DE/MS, achieving identification of all the major sheep milk proteins and their localization in reference maps. Reproducibility of MFGP maps was then assessed; no significant variations were detectable when comparing samples from different healthy animals at the same stage of lactation. These results provide the first 2-DE reference map of sheep MFGPs, opening the way to studies on their expression in different physiological and pathological conditions.