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PubMed1988

The secondary structure of peptides derived from caseins: a circular dichroism study.

Three peptides have been formed by proteolytic digestion of individual casein proteins and their secondary structures characterised by far-UV circular dichroism (CD). Peptide alpha s1(1-23), residues 1-23 of alpha s1-casein, was generated by treatment of the parent protein with chymosin. Peptides beta(1-28) and beta(1-52), residues 1-28 and 1-52 of beta-casein, were plasmin- and chymotrypsin-generated fragments, respectively. Analysis of the CD spectra revealed that in aqueous solution all three peptides have secondary structures composed exclusively of beta-sheet and random coil. A limited amount of alpha-helix was formed in two of the three peptides upon treatment with high concentrations (greater than 40% (v/v] of 2,2,2-trifluoroethanol. Partial dephosphorylation (60%) of beta(1-28) and beta(1-52) by treatment with alkaline phosphatase resulted in homogeneous preparations, as judged by polyacrylamide gel electrophoresis, which exhibited increased hydrophobicity. This reduction in the level of phosphorylation of serine residues 15, 17, 18 and 19 led to increased propensity for helix formation in the peptides in the presence of 2,2,2-trifluoroethanol, but no alpha-helical structures were detected in the dephosphorylated peptides in the absence of 2,2,2-trifluoroethanol.

Amino Acids↗
PubMed1991

Characterization of phosphopeptide derived from bovine beta-casein: an inhibitor to intra-intestinal precipitation of calcium phosphate.

Casein phosphopeptide (CPP), a highly phosphorylated peptide fragment which inhibits the formation of hydroxyapatite crystal was isolated from pooled ileal contents of rats fed a semi-synthetic diet containing bovine beta-casein. The estimated amino acid sequence of the CPP was shorter than that of the trypsin-digested beta-casein but the core region consisting of consecutive bindings of phosphoserine was fully conserved. A moderate and exchangeable binding to Ca2+ of the CPP molecule well substantiates the high absorbability of calcium from milk and dairy products.

Amino Acid Sequence↗
PubMed1989

Random tyrosine and glutamic acid-containing polymers are very powerful inhibitors of casein kinase-2.

The random heteropolymers Glu/Tyr(4:1) and Glu/Tyr(1:1) that are widely used as substrates for tyrosine protein kinases, are very powerful competitive inhibitors of casein kinase-2, but not of casein kinase-1, with respect to the protein substrate, their Ki values being one to two orders of magnitude lower than those of polyglutamates of similar size. The inhibitory power is reduced if tyrosine is partially replaced by alanine, as in the polymer Glu/Ala/Tyr(6:3:1) and it disappears upon inclusion of lysine, the polymer Glu/Ala/Lys/Tyr(2:6:5:1) actually behaving as a stimulator. These data indicate that non-phosphorylatable hydroxylic residues in addition to acidic ones are required in order to optimize the binding of pseudo-substrates to the catalytic site of casein kinase-2.

Casein Kinases↗
PubMed1995

The protein kinase from mitotic human cells that phosphorylates Ser-209 on the casein kinase II beta-subunit is p34cdc2.

Casein kinase II is a highly conserved enzyme that is essential for viability. In cells, the casein kinase II beta-subunit is phosphorylated at an autophosphorylation site and at a site (Ser-209) that is maximally phosphorylated in mitotic cells. To identify protein kinase activities that phosphorylate Ser-209, we fractionated extracts from mitosis-arrested human Burkitt lymphoma MANCA cells. A single Ser-209 kinase activity was detected following each fractionation step. The Ser-209 kinase was purified to a specific activity of approx. 250 nmol/min per mg and efficiently phosphorylated histone H1, a synthetic peptide containing Ser-209 (Ser-209 peptide), myelin basic protein and casein. Immunoblot analysis demonstrated that all fractions containing Ser-209 kinase activity contained p34cdc2. Furthermore, depletion of the Ser-209 kinase activity with p13suc1-Sepharose and anti-p34cdc2 antiserum demonstrated conclusively that the isolated Ser-209 kinase is p34cdc2. These studies provide strong biochemical evidence that p34cdc2 is the enzyme that phosphorylates Ser-209 on the beta-subunit of CKII in mitotic cells. In addition, these results indicate that the Ser-209 peptide can be utilized as a specific reagent for the assay of p34cdc2 activity in mitotic extracts, since no other Ser-209 peptide kinase activities were detected.

Amino Acid Sequence↗
PubMed1991

Characterisation of the influenza virus associated protein kinase and its resemblance to casein kinase II.

The protein kinase activity associated with purified influenza virus has been examined. By use of a radiolabelled photoreactive ATP analogue (3'-O-(4-benzoyl) benzoyl adenosine triphosphate) a 47 kD polypeptide has been identified that binds ATP. A comparison of the sensitivity of the kinase activity and the 47 kDa polypeptide labelling to inhibitors indicate that the 47 kDa polypeptide is likely to represent the major protein kinase activity of the virus. The virus associated protein kinase phosphorylates the synthetic peptide RREEETEEE, a peptide substrate for casein kinase II. Antiserum directed against casein kinase II revealed a positive signal in immunoblots of purified virus. We propose that the major protein kinase activity associated with purified virus preparations is host cell casein kinase II.

Adenosine↗
PubMed1995

A combined casein-free-nicotinamide diet prevents diabetes in the NOD mouse with minimum insulitis.

We have previously shown that diabetes in the NOD mouse can be prevented if mice are placed from weaning on an infant formula diet in which the protein source is replaced with casein hydrolysate (Pregestimil) or soy protein (Prosobee), or if 1% nicotinamide is given in the drinking water. Nicotinamide somewhat suppresses insulitis but the hydrolysed casein formula does not. In this study, Prosobee was given concurrently with oral nicotinamide from weaning and their effects on the development of insulitis and diabetes measured. These effects were also assessed in mice given Prosobee alone from conception (day -20) or from weaning. Unlike the earlier experiments, a marked suppression of insulitis was observed when the diets and nicotinamide were given concurrently (mean insulitis scores +95% confidence intervals (back transformed): day 40 = 0.4% [0.03, 1.17] vs. 12.5% [2.52, 28.40] and at day 90 = 8.8% [3.65, 15.68] vs. 48.1% [33.89, 62.49], P = 0.0001). A similar suppression was observed on day 90 with Pregestimil combined with nicotinamide 7.3% [3.88, 11.70] vs. 43.8% [32.59, 55.35] (P = 0.0001). Qualitatively, introduction of Prosobee from conception appeared to elicit a greater degree of suppression of insulitis than when introduced from day 21. Insulitis lesions were examined immunohistochemically for CD4, CD8 and MAC-1 cells. The proportion of these cells was not different for any regime despite the great differences in total number of inflammatory cells in and around the islets of mice fed the combined diet. All the three dietary treatments (Prosobee from day -20, Prosobee from day 21, Prosobee+nicotinamide from day 21) resulted in substantial protection from diabetes in mice followed until 250 days. We conclude that the complete prevention of diabetes in the NOD mouse fed a casein-free diet together with nicotinamide is accompanied by marked inhibition of insulitis, which is not seen when either dietary agent is introduced alone. The somewhat greater suppression of insulitis in mice given the soy diet from conception compared to those fed from day 21 may indicate that even maternal diet during gestation may influence diabetes outcome in the offspring.

Animals↗
PubMed1993

Phosphorylation of two human neurochordins by mammalian casein kinase 1.

Neurochordins are a family of immunologically interrelated high-M(r) neural tissue glycoproteins which includes four major molecular species and several minor ones. Incubation of the total preparation of immunoaffinity-isolated neurochordins with ATP and rabbit casein kinase 1 resulted in phosphorylation of two neurochordin polypeptides, A and B3. The maximum levels of modification were 7-8 and 2 mol of 32P incorporated per 1 mol of polypeptide, respectively. Phosphoamino acid analysis of the phosphorylated neurochordins showed that casein kinase 1 modified exclusively serine residues in both polypeptides. Casein kinase 2 was not effective in phosphorylating neurochordins in vitro.

Adenosine Triphosphate↗
PubMed1994

Two monoclonal antibodies against prolactin-receptor are internalized in epithelial mammary cells without mimetic prolactin effect on casein secretion.

Prolactin exerts an early stimulatory effect on casein secretion which was qualified as a secretagogue effect. After binding to its receptor, the hormone transits intracellularly through the mammary epithelial cell. When this transit is slowed down the secretagogue effect does not occur. Different monoclonal antibodies which bind to the rabbit prolactin receptor have been previously developed. One of them (A917) mimics prolactin effect on casein gene expression. Another (M110) blocks this prolactin effect. In order to study the respective role of the hormone and its receptor, we have examined the binding of the two monoclonal antibodies (M110 and A917), labeled with biotin or colloidal gold, to the receptor of lactating rabbit mammary epithelial cells in incubation. Subsequently, the intracellular movement of these antibodies and the secretory response have been measured. Irrespective of the labeling (biotin or colloidal gold) or the preparation of tissues (fragments or enzymatically dissociated cells), M110 and A917 bound to the basal membrane of mammary epithelial cells. However, only M110 bound to apical membrane of dissociated cell when this membrane was in direct contact with the incubation medium, showing that the two antibodies discriminate the receptor located on the apical membrane. Following internalization, each antibody was carried via a peculiar pathway. M110 remained associated with the cells during a 1-h incubation, mainly in endosomes, multivesicular bodies and lysosomes like vesicles. In contrast, A917 was very quickly detectable in endosomes, multivesicular bodies and vesicles of the Golgi region and was carried throughout the cell to the lumen of the acini. M110 and A917 were extremely rare in secretory vesicles containing casein micelles.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1996

Antibacterial and immunostimulating casein-derived substances from milk: casecidin, isracidin peptides.

Apart from immunoglobulin A and G antibodies and plasma cells, milk also contains antibiotic/host protective peptides that are of value not only for maintenance of its nutritional integrity but also for protection of the newborn and, possibly, protection of the lactating mother. Among the first such peptides identified with casecidin; following chymosin digestion of casein at pH 6 or 7, casecidin inhibited in vitro staphylococci, sarcina, Bacillus subtilis, Diplococcus pneumoniae and Streptococcus pyogenes. Inhibition occurred at high concentrations, in vitro, compared with commercial antibiotics, and thus interest in casecidin languished. Work with casecidin was followed by investigation of a related refined non-immunogenic product of chymosin digestion of alpha s1-casein. This product consisted of the N -terminal segment (1-23) of alpha s1-casein B, named "isracidin", and was significantly effective in vivo at concentrations that were competitive with known antibiotics, as seen in the protection of mice against lethal infection by Staphylococcus aureus strain Smith. Field trials showed that injection of isracidin into the udder gave protection against mastitis in sheep and cows. Isracidin was both therapeutic and prophylactic and responses to its therapeutic effect produced long-term immune resistance. Isracidin protected mice against Candida albicans, by stimulation of both phagocytosis and immune responses. However, like other recently described milk-derived peptides, despite its clinical value, isracidin was overlooked because of the lack of commercial interest in the 1970s and early 1980s, in host-mediated non-specific resistance as a therapeutic approach to infection. Another problem that impeded commercial interest was the isomeric variation in isracidin peptides seen on a large-scale batch production for commercial use. It is hoped that this review of previous studies of the activity of isracidin action will revive interest in milk as an antibiotic source.

Adjuvants, Immunologic↗
PubMed1976

Model calculations of casein micelle size distributions.

A previously proposed model for the formation and structure of casein micelles from subunits of variable composition is used to calculate theoretical micelle size distributions. Using the fractional content of k-casein as the only variable but with a value near that observed in a sample of milk serum, the model successfully reproduces experimentally determined distributions. Predicted size distributions are quite sensitive to the value of the variable and shift toward smaller average size as the assumed fractional content k-casein gets larger. Also, there is a discontinuity in the distributions which predicts that there will be essentially no micelles with radii smaller than 25-30 nm. These predictions are all in accord with experimental observations. The good agreement between theory and experimenet supports the micelle structure suggested by the model.

Binding Sites↗
PubMed1980

A mechanism for the chymosin-induced flocculation of casein micelles.

The chymosin-induced flocculation of casein micelles of bovine milk can be explained and calculated in terms of three relationships, which are (i) the action of chymosin upon the kappa-casein of the micelles; (ii) the probability that a micelle, with a given proportion of its kappa-casein destroyed, will aggregate, and (iii) the aggregation of micelles by a Smoluchowski mechanism. Details of the calculations are given, and the theory is shown to be in good agreement with experimental observations of the dependence of the clotting time with variations in enzyme and substrate concentrations.

Animals↗
PubMed1989

Basic fibroblast growth factor stimulates the growth and inhibits casein accumulation in mouse mammary epithelial cells in vitro.

The effects of basic fibroblast growth factor (bFGF) on the growth and differentiation of mouse mammary epithelial cells in serum-free collagen gel culture were examined. Epithelial cells obtained from virgin or midpregnant mice grew when bFGF was added to medium containing either insulin at a concentration greater than or equal to 1 microgram/ml or somatomedin-C (Sm-C) at 150 ng/ml. This growth-promoting effect is of the same magnitude as, and additive with, the growth-promoting effect of epidermal growth factor (EGF) or mammogenic hormones. The sensitivity of the cells to EGF or mammogenic hormones was not altered by exposure to bFGF. The progeny cells resulting from growth stimulation by bFGF are capable of accumulating casein upon subsequent stimulation by prolactin (PRL), but accumulate less casein than cells grown in response to EGF. bFGF also appears to reduce casein accumulation if it is added to the cultures at the same time as PRL.

Animals↗
PubMed1989

The actions of forskolin, cholera toxin and iloprost on casein secretion by lactating doe mammary glands.

The secretagogue effects of prolactin (PRL) and of various agents acting on cAMP levels, forskolin, cholera toxin and iloprost (a stable analogue of prostaglandin I2) have been assessed in lactating doe mammary gland fragments in vitro. Forskolin (10 microM), cholera toxin (1 microgram/ml) and iloprost (10 mM) stimulated milk casein secretion. The effects of forskolin (10 microM) and cholera toxin (1 microgram/ml) were potentiated by PRL (10 micrograms/ml). Conversely, the action of iloprost (10 microM) was not amplified by PRL (10 micrograms/ml). Forskolin (10 microM) and cholera toxin (1 microgram/ml) stimulated the intracellular accumulation of cAMP. Neither PRL nor iloprost, at concentrations which stimulated casein secretion, modified the accumulation of cAMP. These results demonstrate that PRL does not act directly by any increase in intracellular cAMP levels. However, stimulating effects of forskolin and cholera toxin on casein secretion and intracellular cAMP levels suggest that various transduction signals are effective in the mammary cells.

Animals↗
PubMed1996

Cloning, sequencing and functional analysis of a truncated cDNA encoding red deer prolactin receptor: an alternative tyrosine residue mediates beta-casein promoter activation.

This study reports the isolation and in vitro characterisation of a truncated cDNA encoding the red deer long form prolactin receptor. The cDNA sequence predicts a protein of 557 amino acids which differs from the rat sequence by a 3' truncation of the cytoplasmic domain located 34 residues before the stop codon. The deer sequence shares the regions of homology which are important for maintenance of structural and functional integrity, high affinity binding and signal transduction. However, the truncated deer receptor lacks the most C-terminal tyrosine residue in the intracellular domain which is believed to be essential for activation of the beta-casein promoter. Transfection studies of the cervine cDNA into human 293 fibroblast cells confirmed the expression of a receptor that has high affinity binding to ovine prolactin (Ka = 0.65 x 10(9)M(-1) and Bmax = 548.6 fmol/mg protein). Co-transfection of CHO cells with expression vector encoding the cervine prolactin receptor cDNA along with a fusion gene containing the promoter region of beta-casein followed by beta-luciferase coding sequence led to 8.13 +/- 0.13-fold induction of luciferase enzyme activity in the presence of 400 ng/ml ovine prolactin. This was comparable to fold induction observed with the wild type long form rat prolactin receptor (6.37 +/- 0.48); macaque growth hormone receptor was without effect. Western blot analysis demonstrated tyrosine phosphorylation of the cervine receptor and the associated kinase Jak2 following stimulation with prolactin. This confirms that the cervine cDNA although truncated is fully functional and that Jak2 and an alternative tyrosine residue in the intracellular domain are involved in the signalling pathway leading to activation of the beta-casein promoter. Northern blot analysis provides evidence that the prolactin receptor in the liver is encoded by transcripts of approximately 2.5 and 3.5 kb. Comparison of Northern blots of different deer species suggests that the receptor is conserved amongst the Cervidae. Northern blot analysis of red deer testis suggests that this species expresses a second form of the receptor, encoded by a transcript of 1.7 kb, which may correspond to a smaller receptor form or a binding protein.

Amino Acid Sequence↗
PubMed1981

The chemical structure of neutral and acidic sugar chains obtained from bovine colostrum kappa-casein.

One neutral oligosaccharide alditol (tetrasacchariditol, 10%) and three acidic oligosaccharide alditols (a tri (28%), tetra (17%) and a pentasacchariditol (44%) were isolated from, colostrum kappa-casein taken 6 h after parturition. The neutral tetrasacchariditol and the acidic pentasacchariditol only contained a characteristic N-acetylglucosamine, and the latter was the main carbohydrate portion. The chemical structures were analyzed by methylation analysis with gas-liquid chromatography-mass spectrometry and by anomer analysis with 13C nuclear magnetic resonance, and were identified to be galactosyl-beta-1-3-[galactosyl-beta-1-4-N-acetylglucosaminyl-beta-1-6-]-N-acetylgalactosaminitol, N-acetylneuraminyl-alpha-2-3-galactosyl-beta-1-3-[galactosyl-beta-1-4-N-acetylglucosaminyl-beta-1-6-]-N-acetylgalactosaminitol, N-acetylneuraminyl-alpha-2-6-N-acetylgalactosaminitol. The former two were the novel carbohydrate chains of colostrum kappa-casein, but the latter two were identical with those which have been found in normal kappa-casein.

Animals↗
PubMed1988

Isolation and characterization of the Bos taurus beta-casein gene.

The expression of casein genes in the mammary cells is regulated by peptide and steroid hormones. To investigate the controlling mechanisms we have isolated and characterized the bovine beta-casein gene. The gene has the size of 8.6 kb, which is 7.8 times longer than the corresponding mRNA composed of nine exons. The genomic clones include additional 8.5-kb and 4.5-kb sequences of the 5'- and 3'-flanking regions. We have determined the sequences of the 5' and 3' ends of the gene and compared them with the respective sequences of the rat beta-casein gene. Conserved sequences are identical or homologous to the potential binding sites for nuclear factors and for glucocorticoid and progesterone receptors. The regulatory region contains two different TATA signals and a repeat sequence between them.

Animals↗
PubMed1987

Heat-stable (STa) enterotoxin of enterotoxigenic Escherichia coli: binding of the enterotoxin to coagulated milk and casein.

Oral or intragastric inoculation of the STa enterotoxin of Escherichia coli has been the standard laboratory test for that toxin. We demonstrated that the severity of the secretory response of 2-4-day-old mice to a single dose of the toxin was influenced by weaning of these mice. After oral application of 50-250 fmol of purified, radioiodinated STa toxin (12-13 Ci mmol-1) approximately 55-65% of the administered toxin bound to the stomach contents. Binding of the toxin did not destroy its biological activity. The binding was pH dependent; stomach contents bound 75% of the toxin at pH 2.3 and only 7.4% at pH 10.1. The principle in the stomach contents which bound the toxin was also demonstrated in murine and bovine milk. Further studies with renin-coagulated milk and commercial casein indicated that milk casein bound the toxin. Based on these findings, we speculate that in cases of food-poisoning involving casein-containing foods STa toxin may be present in the absence of cultivable enterotoxigenic E. coli.

Animals↗
PubMed1992

Exon skipping in human beta-casein.

Earlier amino acid alignments of mature beta-caseins showed that the human protein was shifted in alignment relative to other species, with amino acid deletions in the N-terminal region and others inserted in the C-terminal region. Our alignment, based on cDNA sequences and their translation products, has shown that the amino acid deletions correspond exactly to exon 3 in the other species. Cloning and sequencing of a segment of the human beta-casein gene between exons 2 and 4 revealed the presence of an intact exon 3 sequence in the gene. An interruption of the polypyrimidine tract adjacent to the 5' end of exon 3 sequence may account for the omission of the exon from human beta-casein mRNA.

Amino Acid Sequence↗