Primary structure of kappa-casein isolated from mares' milk.
In this work the purification and the complete primary structure of kappa-casein from equine milk are reported for the first time. Mares' milk casein was separated by RP-HPLC into four fractions. Complete primary sequence was obtained by sequence analysis of the protein in the fastest eluting peak isolated by chromatography. This sequence was 95% identical to that reported for the C-terminal portion of the zebras' kappa-casein and showed high similarity with kappa-caseins from sources other than Equidae, confirming that this protein was indeed kappa-casein in equine milk. The presence of post-translational modifications in equine kappa-casein was investigated by mass spectroscopy, after enzymic dephosphorylation. Two main components were found, the smaller component being more abundant. Equine kappa-casein was recognized by a lectin specific for one of the glucosidic bonds in the saccharide moiety of bovine kappa-casein. Sequence comparison with prevision studies showed that the distribution of charged and hydrophobic regions in equine kappa-casein was similar, but not identical, to that found in the bovine protein; these regions are associated with the role of kappa-casein in the formation and stabilization of the micellar structure of casein in milk.
Iametti
B S
BS
Dipartimento di Scienze Molecolari Agroalimentari, Università degli Studi di Milano, Italy. stefania.iametti@unimi.it
Tedeschi
G
G
Oungre
E
E
Bonomi
F
F
D000595:Amino Acid Sequence; D000818:Animals; D002364:Caseins / Q000032:analysis / Q000737:chemistry* / Q000302:isolation & purification; D002851:Chromatography, High Pressure Liquid; D005260:Female; D006736:Horses / Q000378:metabolism*; D013058:Mass Spectrometry; D008823:Micelles; D008892:Milk / Q000737:chemistry*; D008894:Milk Proteins / Q000032:analysis / Q000737:chemistry; D008969:Molecular Sequence Data; D020539:Sequence Analysis, Protein / Q000662:veterinary
D002364:Caseins; D008823:Micelles; D008894:Milk Proteins