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PubMed1975

Preparation and properties of alpha S-casein from buffalo's milk.

Buffalo alpha S-casein (alpha-sb) was found to be heterogenous; on starch gel-urea electrophoresis 4 electrophoretic components were detected. The alpha-sb-fraction was isolated by urea and alcohol fractionation. A preparation containing only the 2 main components was obtained by chromatography on DEAE-cellulose. Its amino acid pattern was different from that of cow alpha s1-casein. The fraction was also free of carbohydrate, cystine and cysteine. Buffalo alpha-sb-casein was less stable than cow alpha s-casein in solutions containing Ca, and the maximum stability of the alpha s-/k-casein complex occurred at a lower Ca concentration.

Amino Acids↗
PubMed1975

Preparation and properties of beta-casein from buffalo's milk.

Beta-casein from individual buffalo's milk was found to be homogeneous by starch-gel electrophoresis. Beta-Casein was separated from buffalo's milk by the method of Warner (1944) and purified by DEAE-cellulose chromatography. Buffalo beta-casein possesses identical end-groups to those of cow beta-casein; namely N-terminal arginine and assuming a single polypeptide chain a possible C-terminal sequence of Ile-Ile-Val. However, the amino-acid composition and the trypic peptide patterns of the 2 proteins are not the same.

Amino Acid Sequence↗
PubMed1979

Post-secretory aggregation of caseins.

Particles as large as several micrometer diam. have been observed occasionally in normal milk and commonly in prepartum and postpartum colostrum. These particles can be dissociated by EDTA and their appearance closely resembles that of normal casein micelles. However, they are often too large to have been completely formed within the Golgi vesicles of mammary epithelium and hence some degree of post-secretory aggregation of caseins is thought to occur. Two possible mechanisms of post-secretory aggregation of caseins are: (1) a continuation of the normal processes of micelle assembly in the alveolus and (2) aggregation as a result of limited proteolysis of the caseins during the time the milk is in the mammary gland. Incubation of milk with fibrinolysin, however, failed to produce aggregation of normal micelles.

Animals↗
PubMed1979

The binding of beta-casein to hydroxyapatite: the effect of phosphate content and location.

The elution behaviour of beta-casein from columns of hydroxyapatite has been studied and the effect examined of the enzymic addition of an extra phosphate residue. When the additional phosphate is located near pre-existing phosphate residues stronger binding to hydroxyapatite is observed. When the additional phosphate is remote from the pre-existing phosphates no increase in strength of binding is observed. It is suggested that the clustering of phosphate residues which characterizes alphas- and beta-caseins can be rationalized on the basis that it facilitates co-operative interactions between these phosphates and the Ca phosphate of the casein micelle and/or basic residues within casein polypeptide chains.

Amino Acid Sequence↗
PubMed1989

Chemical characterization of bioactive peptides from in vivo digests of casein.

The in vivo formation of biologically active caseinopeptides was studied. It was proved that bioactive peptides were released in the small intestine of minipigs in the course of luminal digestion of diets containing bovine casein. An opioid peptide and a phosphopeptide were isolated from jejunal chyme and were chemically characterized. The opioid peptide has been identified as a fragment of beta-casein (60-70). This peptide, named beta-casomorphin-11, displayed substantial opioid activity in an opiate receptor-binding assay. The caseinophosphopeptide has been shown to be a fragment of alpha s1-casein (66-74). Casein-derived phosphopeptides exhibit a potent ability to form soluble complexes with Ca and trace elements. Evidence exists that casomorphins and caseinophosphopeptides participate in the regulation of nutrient entry.

Animals↗
PubMed1983

Breakdown of caseins by proteinases in bovine milks with high somatic cell counts arising from mastitis or infusion with bacterial endotoxin.

Milk obtained from cows which were either infected by clinical mastitis or had been subjected to intramammary infusion of Escherichia coli endotoxin possessed high counts of somatic cells and very high levels of proteinase activity which hydrolysed the caseins almost completely in a few hours at 37 degrees C. The rate of hydrolysis of beta-casein was slightly greater than that of alpha S1-casein, but in both cases hydrolysis was enhanced by 6 cycles of freezing and thawing to disrupt somatic cell membranes. A study of the relationship between proteinase activity and cell count suggested that only some of the proteinase activity originated in the somatic cells and also that the identity of the cells making up the total cellular population was important. Maximum proteolysis occurred at 50-60 degrees C, but the temperature-activity curve was a broad peak. Likewise the pH versus activity plot was very broad and was almost flat over the pH range 6-9. Experiments with a number of inhibitors of proteinases failed to give a clear cut pattern of inhibition. All evidence obtained was consistent with the view that several different enzymes with different pH and temperature optima and different specificities contributed to the overall hydrolysis of caseins in these milks. From electrophoretic band patterns one of these enzymes was clearly plasmin, but in high cell count milks other proteinases also became significant.

Animals↗
PubMed1998

Sequence analysis of Camelus dromedarius milk caseins.

Alpha s1-, alpha s2-, beta- and kappa-caseins from Somali camels (Camelus dromedarius) were purified by acid precipitation at pH 4.4, crudely separated into an alpha-CN and a beta-CN fraction and further purified by reversed-phase HPLC. Fragments of tryptic digests were sequenced. Amino acid patterns obtained were used to screen a cDNA library constructed from mRNA from lactating udder tissue. Full length clones corresponding to the four caseins were sequenced. The numbers of residues in the sequences deduced were alpha s1-CN 207, alpha s2-CN 178, beta-CN 217, kappa-CN 162. Percentage similarity to bovine proteins was alpha s1-CN A 39, alpha s2-CN 56, beta-CN 64, kappa-CN 56. Acid-precipitated casein of pooled milk was separated by reversed-phase HPLC and monitored at 220 nm, and its composition, estimated from peak integration, was (g/kg total casein) alpha s1-CN 220, alpha s2-CN 95, beta-CN 650, kappa-CN 35. Degrees of phosphorylation and glycosylation were determined by laser ionization mass spectrometry and sequence pattern analysis. Molecular masses determined were (kDa) alpha s1-CN A, 24.755 and 24.668; alpha s1-CN B, 25.293; alpha s2-CN 21.993; beta-CN, 24.900; kappa-CN 22.294-22.987. The pH values of the most probable isoelectric points were: alpha s1-CN A 6P 4.41, alpha s1-CN B 6P 4.40, alpha s2-CN 9P 4.58, beta-CN 4P 4.66, kappa-CN 1P, with ten sialic acid residues bound, 4.10.

Amino Acid Sequence↗
PubMed1998

Identification of a phosphopeptide in bovine alpha s1-casein digest as a factor influencing proliferation and immunoglobulin production in lymphocyte cultures.

Digestion of bovine alpha s1-casein with bovine trypsin produced peptide(s) with an inhibitory effect on concanavalin A-induced proliferation of mouse spleen cells. One of these peptides was isolated from the alpha s1-casein digest following ultrafiltration, hydroxyapatite chromatography and reversed-phase HPLC, and amino acid composition and sequence analyses showed it to be sequence 59-79 from the phosphoserine-rich region of alpha s1-casein. The isolated peptide significantly inhibited the concanavalin A-induced proliferation of mouse spleen cells and rabbit Peyer's patch cells, whereas it enhanced the lipopolysaccharide- and phytohaemagglutinin-induced proliferation of both cells. The peptide displayed mitogenic activity in the cell cultures without the commercial mitogen, and significantly enhanced immunoglobulin production. Moreover, residues 1-25 from the phosphoserine-rich region of bovine beta-casein had a similar effect on the proliferation of mouse spleen cells and rabbit Peyer's patch cells stimulated or not stimulated by the commercial mitogen. These results indicate that caseinophosphopeptides may act as a humoral immunostimulator in cell cultures.

Amino Acid Sequence↗
PubMed1983

Opioid activities and structures of alpha-casein-derived exorphins.

Exorphins, peptides with opioid activity, have previously been isolated from pepsin hydrolysates of alpha-casein [Zioudrou, C., Streaty, R. A., & Klee, W. A. (1979) J. Biol. Chem. 254, 2446-2449]. Analysis of these peptides shows that they correspond to the sequences 90-96, Arg-Tyr-Leu-Gly-Tyr-Leu-Glu, and 90-95, Arg-Tyr-Leu-Gly-Tyr-Leu, of alpha-casein. These peptides, as well as two of their analogues Tyr-Leu-Gly-Tyr-Leu-Glu (91-96) and Tyr-Leu-Gly-Tyr-Leu (91-95), have now been synthesized and characterized. Their opioid activity was examined by three different bioassays: (a) displacement of D-2-alanyl[tyrosyl-3,5-3H]enkephalin-(5-L-methioninamide) and [3H]dihydromorphine from rat brain membranes; (b) naloxone-reversible inhibition of adenylate cyclase in homogenates of neuroblastoma x glioma hybrid cells; (c) naloxone-reversible inhibition of electrically stimulated contractions of the mouse vas deferens. The synthetic peptide of sequence 90-96 was the most potent opioid in all three bioassays and its potency was similar to that of the isolated alpha-casein exorphins. The synthetic peptides were totally resistant to hydrolysis by trypsin and homogenates of rat brain membranes, but were partially inactivated by chymotrypsin and subtilisin. The difference in opioid activity of alpha-casein exorphins may be related to differences in conformational flexibility observed by NMR spectroscopy.

Adenylyl Cyclase Inhibitors↗
PubMed1989

Molecular cloning of the human casein kinase II alpha subunit.

A human cDNA encoding the alpha subunit of casein kinase II and a partial cDNA encoding the rat homologue were isolated by using a Drosophila casein kinase II cDNA probe. The 2.2-kb human cDNA contains a 1.2-kb open reading frame, 150 nucleotides of 5' leader, and 850 nucleotides of 3' noncoding region. Except for the first 7 deduced amino acids that are missing in the rat cDNA, the 328 amino acids beginning with the amino terminus are identical between human and rat. The Drosophila enzyme sequence is 90% identical with the human casein kinase II sequence, and there is only a single amino acid difference between the published partial bovine sequence and the human sequence. In addition, the C-terminus of the human cDNA has an extra 53 amino acids not present in Drosophila. Northern analysis of rat and human RNA showed predominant bands of 5.5, 3.1, and 1.8 kb. In rat tissues, brain and spleen had the highest levels of casein kinase II alpha subunit specific RNA, while skeletal muscle showed the lowest. Southern analysis of human cultured cell and tissue genomic DNA using the full-length cDNA probe revealed two bands with restriction enzymes that have no recognition sites within the cDNA and three to six bands with enzymes having single internal sites. These results are consistent with the possibility that two genes encode the alpha subunits.

Amino Acid Sequence↗
PubMed1989

Cloning and characterization of a cDNA encoding the beta subunit of human casein kinase II.

Previous studies [Summercorn et al. (1987) Proc. Natl. Acad. Sci. U.S.A. 84, 8834-8838; Klarlung & Czech (1988) J. Biol. Chem. 263, 15872-15875] have indicated that Balb/c 3T3 cells and 3T3-L1 adipocytes incubated with insulin show increased casein kinase II activity within minutes, implicating this serine/threonine kinase as an early step in an insulin signaling pathway. We recently reported the isolation of a cDNA encoding an alpha subunit of human casein kinase II [Meisner et al. (1989) Biochemistry 28, 4072-4076] as an initial step toward examining the regulation of this enzyme. We now describe a HepG2 cell casein kinase II beta subunit cDNA of 2.57 kb containing 96 bases of 5' untranslated sequence, 645 bases of open reading frame, and 1832 bases of 3' untranslated sequence with two polyadenylation consensus signal sequences and two poly(A) stretches. The open reading frame of the human beta subunit cDNA was 77% and 87% identical with the Drosophila sequence at the nucleotide and amino acid levels, respectively, and 99% identical with the bovine amino acid sequence. RNA analysis of HepG2 cell RNA utilizing HepG2 beta subunit cDNA fragments as probes revealed one major band migrating at 1.2 kb and two minor bands migrating at 3.0 and 4.2 kb. Results from DNA analysis of HepG2 genomic DNA, consistent with results utilizing Drosophila genomic DNA, suggest the presence of a single gene for the beta subunit of casein kinase II.

Amino Acid Sequence↗
PubMed2006

Dysbindin structural homologue CK1BP is an isoform-selective binding partner of human casein kinase-1.

Casein kinase-1 is a family of ubiquitous eukaryotic protein kinases that frequently function in tandem with the ubiquitin modification system to modulate protein turnover and trafficking. In Alzheimer's disease, these enzymes colocalize with ubiquitinated lesions, including neurofibrillary tangles and granulovacuolar degeneration bodies, suggesting they also play a role in disease pathogenesis. To identify binding partners that potentially regulate or recruit these enzymes toward disease lesions, a Sos-recruitment yeast two-hybrid screen was performed with human Ckidelta (the casein kinase-1 isoform most closely linked to granulovacuolar degeneration bodies) and a human brain cDNA library. All interacting clones contained a single open reading frame termed casein kinase-1 binding protein (CK1BP). On the basis of sequence alignments, CK1BP was a structural homologue of the acidic domain of dysbindin, a component of the dystrophin-associated protein complex and the biogenesis of lysosome-related organelles complex-1. CK1BP interacted with full-length Ckidelta, the isolated Ckidelta catalytic domain, Ckigamma2, -gamma3, and -epsilon in the yeast two-hybrid system, and bound Ckidelta and -epsilon in pulldown assays but did not interact with Ckialpha. Interaction with the Ckidelta catalytic domain led to concentration-dependent inhibition of protein kinase activity in the presence of protein substrates tau and alpha-synuclein. Although intact dysbindin did not bind any CK1 isoform, deletion of its coiled-coil domain yielded a protein fragment that behaved much like CK1BP in two-hybrid screens. These data suggest that the acidic domain of dysbindin and its paralogs in humans may function to recruit casein kinase-1 isoforms to protein complexes involved in multiple biological functions.

Amino Acid Sequence↗
PubMedDate not supplied

Transglutaminase-mediated protein immobilization to casein nanolayers created on a plastic surface.

An enzymatic method for covalent and site-specific immobilization of recombinant proteins on a plastic surface was explored. Using Escherichia coli alkaline phosphatase (AP) with a specific peptide tag (MKHKGS) genetically incorporated at the N-terminus as a model (NK-AP), microbial transglutaminase (MTG)-mediated protein immobilization was demonstrated. To generate a reactive surface for MTG, a 96-well polystyrene microtiter plate was physically coated with casein, a good MTG substrate. Successful immobilization of recombinant AP to the nanolayer of casein on the surface of the microtiter plate was verified by the detection of enzymatic activity. Since little activity was observed when wild-type AP was used, immobilization of NK-AP was likely directed by the specific peptide tag. When polymeric casein prepared by MTG was used as a matrix on the plate, the loading capacity of AP was increased about 2-fold compared to when casein was used as the matrix. Transglutaminase-mediated site-specific posttranslational modification of proteins offers one way of generating a variety of protein-based solid formulations for biotechnological applications.

Alkaline Phosphatase↗
PubMedDate not supplied

Shear characteristics, miscibility, and topography of sodium caseinate-monoglyceride mixed films at the air-water interface.

In this contribution, we are concerned with the study of structure, topography, and surface rheological characteristics (under shear conditions) of mixed sodium caseinate and monoglycerides (monopalmitin and monoolein) at the air/water interface. Combined surface chemistry (surface film balance and surface shear rheometry) and microscopy (Brewster angle microscopy, BAM) techniques have been applied in this study to mixtures of insoluble lipids and sodium caseinate spread at the air-water interface. At a macroscopic level, sodium caseinate and monoglycerides form an heterogeneous and practically immiscible monolayer at the air-water interface. The images from BAM show segregated protein and monoglyceride domains that have different topography. At surface pressures higher than that for the sodium caseinate collapse, this protein is displaced from the interface by monoglycerides. These results and those derived from interfacial shear rheology (at a macroscopic level) appear to support the idea that immiscibility and heterogeneity of these emulsifiers at the interface have important repercussions on the shear characteristics of the mixed films, with the alternating flow of segregated monoglyceride domains (of low surface shear viscosity, etas) and protein domains (of high etas) across the canal.

Air↗
PubMedDate not supplied

Calcium-induced changes to the molecular conformation and aggregate structure of beta-casein at the air-water interface.

The influence of calcium on interactions of beta-casein at the air-water interface has been studied by several techniques, including interfacial rheology, atomic force microscopy (AFM), infrared reflectance-absorbance spectroscopy (IRRAS), and zeta potential measurements. In the absence of calcium, a weak interfacial gel forms after about 2.5 h. Also in the absence of calcium, the adsorbed beta-casein film exhibits some degree of both intra- and intermolecular structural organization. For example, IRRAS spectra show a measurable amount of alpha-helix content, and AFM images indicate the presence of interfacial aggregates with a characteristic lateral length scale of 20-30 nm, which we interpret as hemimicelles. Upon the addition of calcium, particularly at Ca:beta-casein molar ratios above approximately 5:1, a stronger interfacial gel forms more quickly; for example, the interfacial shear moduli increase twice as rapidly. Also under these conditions (5:1 Ca:beta-casein ratio) there is little evidence of structural organization; i.e., the alpha-helix peaks are very weak, and AFM images show a disordered, but continuous film, without distinct hemimicelles. On the basis of these findings, we hypothesize that calcium binding destabilizes the coupled intra- and intermolecular structural organization, and that the loss of organization permits more rapid interfacial gelation. These phenomena are characteristic of the air-water interface; they are not accompanied by analogous structural changes in bulk solution.

Adsorption↗
PubMed2001

Ethanol-dependent heat-induced dissociation of casein micelles.

The dissociation of casein micelles when heated to approximately 65 degrees C in the presence of ethanol [1:1 mixture (v/v) of milk and 65% (w/w) aqueous ethanol] was investigated using L* values and transmission measurements. Mixtures of milk and ethanol became transparent on heating, which suggests dissociation of casein micelles. Results of experiments using confocal laser scanning microscopy, light scattering (static and dynamic), and dialysis to examine the changes of milk during heating in the presence of ethanol supported the assertion that such treatments result in dissociation of casein micelles, as did studies of model beta-casein micellar systems.

Animals↗
PubMed2004

Immunochemical detection of formylated gamma(2)-casein in cheese.

An immunochemical approach has been developed to detect the use of formaldehyde as a bacteriostatic agent in dairy products. A synthetic peptide, reproducing the first five amino acid residues of the gamma(2)-casein sequence, was formylated to generate the novel haptenic structure, already well-recognized in formaldehyde-treated milk and arising out of molecular rearrangement after the addition of formaldehyde to the alpha-amino group of the histidine residue at the N terminus of gamma(2)-casein. A polyclonal antibodies preparation produced against the formylated peptide adduct proved to be a highly specific analytical tool for detecting the formylated adduct of gamma(2)-casein in formaldehyde-treated milk. Polyclonal antibodies obtained against the unmodified peptide were able to detect selectively residual native gamma(2)-casein in ripened cheese.

Antibodies↗
PubMed2004

Identification of angiotensin-I-converting enzyme inhibitory peptides derived from sodium caseinate hydrolysates produced by Lactobacillus helveticus NCC 2765.

Angiotensin-I-converting enzyme (ACE) inhibitory activity was identified in milk proteins fermented with Lactobacillus (Lb.) helveticus NCC 2765 (Nestle Culture Collection, Vers-chez-les-Blanc, Switzerland). Hydrolyzing sodium caseinate for 1 and 2 h inhibited ACE activity, as measured by an in vitro ACE inhibition test. The hydrolysates with the highest ACE inhibitory potential were fractionated by gel permeation chromatography and their low molecular weight fractions collected. These fractions were subsequently subfractionated by reverse-phase high-pressure liquid chromatography. Several hydrophobic subfractions showed high ACE inhibitory potential, and their peptide composition was determined using an ion trap mass spectrometer equipped with an elctrospray ionization source. Analysis of the low molecular weight fraction identified 14 peptides with known antihypertensive activity and 1 with previously described opioid activity. On the basis of the peptide composition of active subfractions, two potentially active novel sequences were defined, and the following synthetic peptides were synthesized: FVAPFPEVFG (alphaS1 39-48), ENLLRFFVAPFPEVFG (alphaS1 33-48), NENLLRFFVAPFPEVFG (alphaS1 32-48), LNENLLRFFVAPFPEVFG (alphaS1 31-48), NLHLPLPLL (beta 147-155), ENLHLPLPLL (beta 146-155), and VENLHLPLPLL (beta 145-155). The ACE inhibitory potential of these synthetic peptides was assessed, and IC50 values were determined. NLHLPLPLL (beta 147-155), which was the only synthetic peptide also present in the sodium caseinate hydrolysates, and NENLLRFFVAPFPEVFG (alphaS1 32-48) showed the highest inhibition of ACE activity, with IC50 values of 15 and 55 microM, respectively. Furthermore, the stability of all synthetic peptides was assessed using an in vitro model simulating gastric digestion. The beta-casein-derived peptides remained intact following the successive hydrolysis by pepsin and pancreatin, whereas alphaS1-casein-derived peptides were degraded by pepsin.

Amino Acid Sequence↗