Structural and functional aspects of three major glycoproteins of the human milk fat globule membrane.
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.
Peterson
J A
JA
Cancer Research Institute of Contra Costa, San Francisco, CA 94107, USA.
Scallan
C D
CD
Ceriani
R L
RL
Hamosh
M
M
D000890:Anti-Infective Agents; D000954:Antigens, Surface / Q000737:chemistry / Q000502:physiology; D000071797:Butyrophilins; D006017:Glycolipids / Q000737:chemistry*; D006023:Glycoproteins / Q000737:chemistry*; D006801:Humans; D066292:Lipid Droplets; D008562:Membrane Glycoproteins / Q000737:chemistry / Q000502:physiology; D008894:Milk Proteins / Q000737:chemistry; D008895:Milk, Human / Q000737:chemistry*; D018396:Mucin-1 / Q000737:chemistry / Q000502:physiology
D000890:Anti-Infective Agents; D000954:Antigens, Surface; D000071797:Butyrophilins; D006017:Glycolipids; D006023:Glycoproteins; C098942:MFGE8 protein, human; D008562:Membrane Glycoproteins; D008894:Milk Proteins; D018396:Mucin-1; C110367:milk fat globule