Primary sequence of kappa-casein

Genotoxicity Study of Glycopeptide (G-7%NANA)

Glycomacropeptide (GMP), a whey protein of milk, has functions including differentiation and development of nervous system, and anticancer and antiviral effects. To develop new functions, N-acetylneuraminic acid (NANA) containing 7% sialic acid was separated from GMP to produce G-7%NANA. N-glycolylneuraminic acid (Neu5Gc) is another type of sialic acid separated from GMP, which has been linked to immune disorders and chronic inflammation-mediated diseases. Therefore, safety was a concern in the use of G-7%NANA in functional foods. To ensure safety, in this study, three genetic toxicity tests on G-7%NANA were conducted. In the reverse mutation test using Salmonella typhimurium TA98, TA100, TA1535, TA1537, and Escherichia coli WP2uvrA, and in the chromosome aberration test using CHO-K1 cells, no significant differences from negative control were found at all dose levels. Similarly, no dose-related differences were evident compared to negative control in the micronucleus test using ICR mice. There was no evidence of G-7%NANA-related genetic toxicity.

Repeated dose 90-day oral toxicity test of G-7% NANA in rats: An application of new criterion for toxicity determination to test article-induced changes

G-7% NANA is N-acetylneuraminic acid(NANA) containing 7% sialic acid isolated from glycomacropeptide (GMP), a compound of milk. Since NANA is likely to have immunotoxicity, the need to ensure safety for long-term administration has been raised. In this study, a 90-day repeated oral dose toxicity test was performed in rats using G-7% NANA in the dosages of 0, 1250, 2500 and 5000 mg/kg/day.A toxicity determination criterion based on the significant change caused by the administration of the substancewas developed for estimating NOEL, NOAEL and LOAELapplied to this study. When analyzing the immunological markers, no significant changes were observed, even if other significant changes were observed in the high dose group. In accordance with the toxicity determination criterion developed, the NOEL in male and female has been determined as 2500 mg/kg/day, and the NOAEL in females has been determined as 5000 mg/kg/day. The toxicity determination criterion, applied for the first time in the repeated dose toxicity tests, could provide a basis for distinguishing NOEL and NOAEL more clearly; nevertheless, the toxicity determination criterion needs to be supplemented by adding differentiating adverse effects and non-adverse effects based on more experiences of the repeated dose toxicity tests.

Recombinant analogs of a novel milk pro-apoptotic peptide, lactaptin, and their effect on cultured human cells

We recently isolated and characterized a human milk peptide, lactaptin, which induced apoptosis of cultured human MCF-7 cells. Lactaptin was identified as a proteolytic fragment of human kappa-casein. Here, we generated two recombinant analogs of the peptide, RL1 and RL2, containing truncated and complete amino acid sequences of lactaptin, respectively. Analogs were produced in E.coli, purified and assayed for biological activity on cultured human MCF-7 cells. RL1 was shown to induce only a small decrease in cell viability, whereas RL2 lowered the viability of MCF-7 cells by 60%. This reduction in MCF-7 cell viability was associated with apoptosis, which was indicated by phosphatidilserine externalization and caspase-7 activation. The viability of A549 and Hep-2 cells was also reduced by RL2, albeit to a lesser degree than seen with MCF-7 cells; this reduced viability was not accompanied by apoptosis. Non-malignant human mesenchymal stem cells (MSC) were completely resistant to RL2 action.

Localization of glycosylated κ-casein in bovine casein micelles by lectin-labelled gold granules

The localization of glycosylated k-casein in isolated bovine casein micelles was investigated at the ultrastructural level with gold granules labelled with the Ricinus communis lectin specific for galactose. No evidence was obtained for the presence of glycosylated k-casein on the surface of glutaraldehyde-fixed micelles whether or not they had been treated with neuraminidase. Glycosylated k-casein was mainly located in the bridging network interconnecting the micelles and appeared to be loosely associated with the micelles. When thin sections of micelles were marked, no clear-cut evidence was observed for the presence of intramicellar glycosylated k-casein.

Nomenclature of the Proteins of Cows’ Milk—Sixth Revision

This report of the American Dairy Science Association Committee on the Nomenclature, Classification, and Methodology of Milk Proteins reviews changes in the nomenclature of milk proteins necessitated by recent advances of our knowledge of milk proteins. Identification of major caseins and whey proteins continues to be based upon their primary structures. Nomenclature of the immunoglobulins consistent with new international standards has been developed, and all bovine immunoglobulins have been characterized at the molecular level. Other significant findings related to nomenclature and protein methodology are elucidation of several new genetic variants of the major milk proteins, establishment by sequencing techniques and sequence alignment of the bovine caseins and whey proteins as the reference point for the nomenclature of all homologous milk proteins, completion of crystallographic studies for major whey proteins, and advances in the study of lactoferrin, allowing it to be added to the list of fully characterized milk proteins.

Glycosylation of kappa-casein. I. Localization and characterization of sialyltransferase in bovine mammary gland

A sialyltransferase (CMP-N-acetylneuraminate:D-galactosyl-glycoprotein N-acetylneuraminyltransferase, EC 2.4.99.1) which attaches N-acetylneuraminic acid to the terminal end of the carbohydrate chain of kappa-casein was found to be concentrated in Golgi apparatus-enriched fractions of bovine mammary gland. Maximum sialyltransferase activity was obtained at pH 5.5 and 37 degrees C in the presence of 1 mM dithiothreitol and Triton X-100. A Km of 0.19 mg asialo-kappa-casein/ml (0.01 mM) was obtained for the sialyltransferase. Native kappa-casein also served as acceptor for N-acetylneuraminic acid transferase of Golgi apparatus-enriched fractions although at a slower rate than did asialo-kappa-casein. The sialyltransferase has a divalent cation requirement for maximum activity which was best satisfied by the presence of 10 mM Mn2+.

Interaction of sodium dodecyl sulfate and of non-ionic detergents with S-carboxyamidomethyl-k-casein

Sodium dodecyl sulfate binds to S-carboxyamidomethyl-k-casein in a highly cooperative manner at a concentration near the critical micelle concentration, showing a strong dependence on ionic strength. The maximum number of sodium dodecyl sulfate molecules bound is attained above the critical micelle concentration, and is very close to the micelle aggregation number in the absence of protein. The binding sites on the protein for sodium dodecyl sulfate are localized mainly on para-k-casein part, which is a hydrophobic fragment of k-casein produced by rennin attack. The mode of the action of sodium dodecyl sulfate on S-carboxyamidomethyl-k-casein resembles that of several integral membrane proteins, rather than of water soluble proteins. On considering possible situations, it is suggested that the unusual interaction of S-carboxyamidomethyl-k-casein with sodium dodecyl sulfate is responsible for an anomalous migration of reduced k-casein observed in sodium dodecyl sulfate polyacrylamide gel electrophoresis. Further, the suggestion was made by the binding studies of sodium dodecyl sulfate and non-ionic detergents that the sites which were involved in self-association of S-carboxyamidomethyl-k-casein participated in the binding sites of detergents.

Molecular weights of three mouse milk caseins by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and kappa-like characteristics of a fourth casein

Caseins of mouse milk are phosphoproteins which precipitate at pH 4.6, stain blue with "Stains-all," and stain red with "Stains-all" following alkaline phosphatase digestion. Four caseins were separated electrophoretically in sodium dodecyl sulfate-polyacrylamide gels varying from 8.5 to 15% acrylamide. Molecular weights for three of these proteins were 43,200, 27,700, and 25,900. The molecular weights determined for bovine alphas1 and beta caseins by this method were similar to those previously obtained by other methods. A fourth mouse casein contained carbohydrate, phosphorus, and sialic acid. This protein was rennin-sensitive and behaved anomalously on sodium dodecyl sulfate polyacrylamide gels, as did bovine kappa-casein. Because of similarities with bovine kappa-casein, it was designated with "kappa-casein" of mouse milk.