Structural and functional aspects of three major glycoproteins of the human milk fat globule membrane.

Cancer Research Institute of Contra Costa, San Francisco, CA 94107, USA.

The MUC1 mucin, lactadherin, and butyrophilin are 3 major components of the human milk fat globule membrane. The mucin inhibits binding of S-fimbriated Escherichia coli to buccal epithelial cells, and lactadherin prevents symptomatic rotavirus infection in breast-fed infants. Butyrophilin has been suggested to be a structural component of the human milk fat globule (HMFG) membrane and to have receptor functions, but has no known anti-infective activity. These HMFG glycoproteins also are present in skimmed milk, possibly associated with phospholipid micelles, while mucin is also in a soluble form. Mucin and lactadherin resist digestion in the stomach of milk-fed infants, while butyrophilin is rapidly degraded. The MUC1 mucin is an extended rod-like structure forming part of the glycocalyx on the surface of many epithelial cells and membranes of milk, and may act as a decoy for binding of infective agents. The extracellular segment of butyrophilin has homology to Ig superfamily receptors and an intracellular domain with homology to developmentally regulated proteins. Lactadherin is a laterally mobile cell adhesion molecule that interacts with integrins and has a novel means of membrane-association involving specific binding to phosphatidylserine. The structural and functional aspects of these glycoproteins are discussed with regard to their role in human milk for breast-fed infants.

PMID: 11787681 [PubMed - indexed for MEDLINE]