Disulphide bonds in casein micelle from milk.
Mammary epithelial cells synthesised and secreted caseins, the major milk proteins in most mammals, as large aggregates called micelles into the alveolar lumen they surround. We investigated the implication of the highly conserved cysteine(s) of kappa-casein in disulphide bond formation in casein micelles from several species. Dimers were found in all milks studied, confirming previous observation in ruminants. More importantly, the study of interchain disulphide bridges in mouse and rat casein micelles revealed that any casein possessing a cysteine is engaged in disulphide bond interchange; these species express four or five cysteine-containing caseins, respectively. We found that the main rodent caseins form both homo- and heterodimers. Additionally, disulphide bond formation among milk proteins was specific since the interaction of the caseins with cysteine-containing whey proteins was not observed in native casein micelles.
Institut National de la Recherche Agronomique, Laboratoire de Génomique et Physiologie de la Lactation, Jouy-en-Josas, F-78352, France.
Edwige
E
Bouguyon
Christian
C
Beauvallet
Jean-Claude
JC
Huet
Eric
E
Chanat
D000595:Amino Acid Sequence; D000818:Animals; D001665:Binding Sites; D002364:Caseins / Q000737:chemistry*; D017124:Conserved Sequence; D004220:Disulfides / Q000032:analysis / Q000737:chemistry*; D051379:Mice; D008807:Mice, Inbred BALB C; D008823:Micelles; D008892:Milk / Q000737:chemistry*; D008969:Molecular Sequence Data; D011485:Protein Binding; D011817:Rabbits; D051381:Rats; D017208:Rats, Wistar; D017386:Sequence Homology, Amino Acid; D013045:Species Specificity
D002364:Caseins; D004220:Disulfides; D008823:Micelles