Table 2.
Properties of major human milk fat globule membrane (MFGM) proteins.
| Protein | Molecular weight (kDa) | Location in milk fraction | Function | Difference with bovine MFGM | Change over lactation | Glycosylated (Y/N) | Resistance to digestion |
|---|---|---|---|---|---|---|---|
| Butyrophilin subfamily 1 member A1 (BTN1A1) | 56 | MFGM | Milk fat globule secretion, immune system | Higher in human than in bovine MFGMa | Higher in mature MFGM than in colostrum MFGMa,c | Y | Rapidly digested in the infant stomachf but more resistant to pepsin compared to XORg; well digested by trypsin and by pronase Eh |
| Mucin 1 (MUC 1/PAS 0) | 250-450 | MFGM | Immune protection | Lower in human than in bovine MFGM, but not significant (P > 0.05)b | No significant change reported in human MFGM; but in bovine MFGM higher at d7 (7.7-fold) compare to colostrumd | Y | Significantly resistant to gastric digestion and may survive to the distal gutf,i; detected in feces of breastfed infants |
| Mucin 4 (MUC 4) | 232 | MFGM | Immune protection | Higher in human MFGM (P < 0.05); not detected in bovine MFGMb | No significant change reportedc | Y | Not specified, but likely be resistant to digestion due to the heavy glycosylation as glycoproteins tend to be resistant to proteases relative to non-glycoproteinsj |
| Xanthine oxidase (XDH/XO, XOR) | 145 | MFGM | Milk fat globule secretion, immune system | Lower in human than in bovine MFGMe; but not significant in another study (P > 0.05)b | Highest at 6 months during 12 months lactationc | Y | Resistant to hydrolysis by trypsin and partially attacked by pronase Eh |
| Lactadherin (PAS VI/VII, MFG-E8) | 43 | MFGM | Immune system | Lower in human than in bovine MFGM (P < 0.05)b | No significant change reportedc | Y | Resistant to human neonatal gastric juice digestion at pH 4 (bovine lactadherin)i; detected intact in gastric aspirate samples of preterm-infantsf; resistant to hydrolysis by trypsin and partially attacked by pronase Eh |
| Cluster of differentiation 14 (CD14) | 40 | MFGM | Immune system | Higher in human than in bovine MFGM (P < 0.05)b ; CD36 was dominant in bovine MFGMd | Not specified | Y | Resistant to pepsinj |
| Adipophilin (ADPH) | 52 | MFGM | Milk fat globule secretion | Not specified | No significant change reported in human MFGM; but in bovine MFGM 3.4-fold upregulated at day 7 compared to colostrumd | N | Well digested by trypsin and by pronase Eh |
| Fatty-acid binding protein (FABP) | 13 | Whey and MFGM | Fatty acid transport, milk fat globule lipid synthesis, | Higher in human than in bovine MFGM (no P value reported)e | Higher at later lactationc | N | Not specified |