Developmental Changes in the Milk Fat Globule Membrane Proteome During the Transition from Colostrum to Milk

Proteomics is a tool that will help identify proteins important to milk production, secretion, as well as specific components in milk.  Identification of proteins associated with various aspects of milk production and secretion will provide a foundation for new research in lactation biology.  Milk fat secretion is an area that needs more molecular details.  The scarcity of information is due in large part to the lack of cell lines that secrete milk and milk fat.  The milk fat globule membrane (MFGM) is a rich source of membrane proteins, and proteomic analysis of these membranes has highlighted some of the transport, signaling, and secretory pathways used by the mammary gland.  Furthermore, the proteome of the MFGM provides additional insight into this membrane’s cellular origin.  The major proteins in the MFGM have been identified using traditional biochemical approaches.  These methods are slow, laborious, and address only one protein at a time.  Proteomic and microarray approaches can identify gene and protein connections to a pathway that is not apparent or predictable from biochemical analysis of a biological system.  In this lecture, we will highlight the use of shotgun proteomics, using amine-reactive isobaric tags to quantify protein changes in bovine MFGM that were isolated from colostrum compared to day 7 milk MFGM.  Finally, we will present the findings of these studies and address some of the challenges to MFGM proteomics that result from the very high abundance of several key MFGM proteins.