Quantitative Phosphoproteomics of Milk Fat Globule Membrane in Human Colostrum and Mature Milk: New Insights into Changes in Protein Phosphorylation during Lactation

Abstract

Phosphorylation is a widespread posttranslational protein modification and is important in various biological processes. However, milk fat globule membrane (MFGM) phosphoproteins have not been explored systematically in human milk. Here, we used quantitative phosphoproteomics to analyze phosphorylation sites in human MFGM proteins and their differences at different stages of lactation; 305 phosphorylation sites on 170 proteins and 269 phosphorylation sites on 170 proteins were identified in colostrum and mature MFGM, respectively. Among these, 71 phosphorylation sites on 48 proteins were differentially expressed between the different stages of lactation. Osteopontin in human MFGM was the most heavily phosphorylated protein, with a total of 39 identified phosphorylation sites. Our results shed light on phosphorylation sites, composition, and biological functions of MFGM phosphoproteins in human colostrum and mature milk, and provide novel insights into the crucial roles of protein phosphorylation during infant development.

Comparative Proteomics of Milk Fat Globule Membrane (MFGM) Proteome across Species and Lactation Stages and the Potentials of MFGM Fractions in Infant Formula Preparation

“…The most shared proteins across species were involved in protein/vesicle-mediated transport, along with major MFGM proteins such as BTN, ADPH, FABP, and MUC1. The main difference regarding human MFGM proteome was a higher enrichment in enzymes involved in lipid catabolism, also reported in Liao et al [ 68 ] and in a set of immune response proteins [ 61 , 72 ].…”

“…These 48 phosphoproteins were mainly associated with immune-related processes. The results showed that there were more immune system process-related phosphoproteins in human colostrum MFGM than in mature MFGM, probably because of the important role that colostrum has in building the immune system of newborns [72].…”

“…This important information helped identify the main proteins with immunity-promoting properties for newborns [66]. Human MFGM phosphoproteome has recently been studied [72]. Phosphorylation is a posttranslational modification that plays a key role in regulating many signaling pathways.…”

“…Human milk proteome varies across colostrum and mature milk [ 71 ], and these variations are also reflected in the MFGM proteome that varies between lactation stages [ 72 ].…”

“…Human MFGM phosphoproteome has recently been studied [ 72 ]. Phosphorylation is a post-translational modification that plays a key role in regulating many signaling pathways.…”