Submitted to: Journal of Dairy Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/6/2006
Publication Date: 11/20/2006
Citation: Reinhardt, T.A., Lippolis, J.D. 2006. Bovine milk fat globule membrane proteome. Journal of Dairy Research. 73(4):406-416. Interpretive Summary: Proteomics is a new technology that allows one to survey and quanitate proteins in tissue of interest and different experimental states. The milk fat globule membrane is the membrane that covers secreted milk fat and is derived from the apical membrane of the secretory epithelium of the mammary gland. The proteins that make up this membrane were identified by mass spectroscopy. The bulk of the proteins identified have functions associated with milk secretion mechanisms, milk fat and protein synthesis and transport. The identity of these proteins will provide important information need to more fully understand milk secretion and production. Functional immune proteins, such as CD14, Toll like receptors 2 and 4 were also identified. This suggests a direct role for the mammary gland in detecting an infection. These findings may result in a new and better understanding of the economical important dairy production disease mastitis.
Technical Abstract: Milk fat globule membranes (MFGM) were isolated from the milk of mid-lactation Holstein cows. The purified MFGM were fractionated using 1-dimensional SDS gels. Tryptic peptides from gel slices were further fractionated on a micro-capillary high-performance liquid chromatograph connected to a nanospray-tandem mass spectrometer. Analysis of the data resulted in 120 proteins being identified by two or more unique peptide sequences. Of these 120 proteins, 71% are membrane associated proteins with the remainder being cytoplasmic or secreted proteins. Only 15 of the proteins identified in the Holstein MFGM were the same as proteins identified in previous mouse or human MFGM proteomic studies. Thus, the bulk of the proteins identified are new for MFGM proteomics. Interestingly, 21% of the proteins identified have unknown functions. The rest of the proteins identified were associated with membrane/protein trafficking (23%), cell signaling (23%), fat transport/metabolism (11%), transport (9%), protein synthesis/folding (7%), immune proteins (4%) and milk proteins (2%). The 46% of the proteins identified that were associated with cell signaling or membrane/protein trafficking may provide insights into MFGM secretion mechanisms. The finding of CD14, TLR2, and TLR4 on MFGMs strongly suggests that pathogens entering the mammary gland are signaled to the host, in part, directly through the mammary gland.