Glycosylphosphatidylinositol-Anchored Proteins in Human and Pig’s Milk

Abstract

Glycosylphosphatidylinositols (GPIs) are a recently discovered class of glycoconjugates that anchor either proteins, polysaccharides or small oligosaccharides to cellular membranes via a covalent linkage. To investigate the presence of soluble GPIs, individual human milk samples and mature pig’s milk were defatted and casein removed by acid precipitation and ultracentrifugation. Soluble proteins were subjected to FPLC gel filtration (Superdex 200) and high molecular weight proteins were separated into fractions I–V. Immunological studies have been performed using Western blotting of whole milk, casein and whey fractions, and Superdex fractions I–V followed by incubation with a monoclonal antibody against the purified GPI anchor of the variant surface glycoprotein from Trypanosoma brucei brucei. We found that significant amounts of GPI-anchored proteins are secreted into human milk and pig’s milk. The antibody which reacted only with components in the whey fractions bound to 5 different human milk proteins with a molecular weight of ≥200 (at least 3 components), 90 and 80 kD. In pig’s milk, the staining pattern was found to be different from human milk. Similar to other GPI-anchored cell structures the functions of GPI-containing proteins in human milk and pig’s milk as well as the specific components carrying these anchors remain to be investigated.

Old and New Stories: Revelations from Functional Analysis of the Bovine Mammary Transcriptome during the Lactation Cycle

“…The pathway is involved in synthesis of GPI which anchors proteins in the membrane of the ER for transport to the Golgi and apical membranes [10]. The importance of the GPI-anchored proteins has not been evaluated in bovine mammary gland and although the concentration of GPI anchored proteins is high in human and pig milk, it is apparently undetectable in bovine milk [11]. GPI-anchors are pivotal for cell survival and affect many functions such as protein sorting in ER-Golgi trafficking, targeting of GPI-anchored proteins in polarized epithelial cells for apical export, cell-to-cell adhesion, signal transduction associated with cholesterol and sphingolipids in membrane rafts, and sorting in endocytic pathways [12].…”

Dynamic changes of fatty acids and minerals in sow milk during lactation

“…Many studies have focused on the composition of milk protein and fat content, rather than the components of milk fat and minerals, especially the changes in fatty acids and minerals during lactation (Kunz, Rudloff, Gundlach, Schuler, & Egge, ; Mountzouris, Fegeros, & Papadopoulos, ; Toledo et al, ). Fat synthesized from glycerine and fatty acids is an important energy source for the growth of livestock.…”