Caseins of various origins and biologically active casein peptides and oligosaccharides: structural and physiological aspects

Kappacin, a novel antibacterial peptide from bovine milk

Caseinomacropeptide (CMP) is a heterogeneous C-terminal fragment (residues 106 to 169) of bovine milk kappa-casein composed of glycosylated and phosphorylated forms of different genetic variants. We have demonstrated that CMP has growth-inhibitory activity against the oral opportunistic pathogens Streptococcus mutans and Porphyromonas gingivalis and against Escherichia coli. CMP was fractionated using reversed-phase high-performance liquid chromatography (RP-HPLC), and each fraction was tested for activity against S. mutans in a 96-well-plate broth assay. Fractions were characterized by N-terminal sequence analysis and mass spectrometry. The active form of CMP was shown to be the nonglycosylated, phosphorylated kappa-casein (residues 106 to 169) [kappa-casein(106--169)], which we have designated kappacin. Endoproteinase Glu-C was used to hydrolyze CMP, and the generated peptides were separated using RP-HPLC and gel filtration-HPLC and then tested for activity against S. mutans. The peptide Ser(P)(149)kappa-casein-A(138--158) was the only peptide generated by endoproteinase Glu-C digestion that exhibited growth-inhibitory activity. Peptides corresponding to the sequences of the inhibitory peptide Ser(P)(149)kappa-casein-A(138--158) and its nonphosphorylated counterpart kappa-casein-A(138--158) were chemically synthesized and tested for antibacterial activity. The synthetic Ser(P)(149) kappa-casein-A(138--158) displayed growth-inhibitory activity against S. mutans (MIC, 59 microg/ml [26 microM]). The nonphosphorylated peptide, however, did not inhibit growth at the concentrations tested, indicating that phosphorylation is essential for activity.

MALDI-PSD-MS analysis of the phosphorylation sites of caseinomacropeptide

Caseinomacropeptide (CMP) is a 64 amino acid polypeptide corresponding to kappa-casein 106-169. CMP naturally exists in several forms due to extensive posttranslational modifications including glycosylation and phosphorylation. The aglycosylated, phosphorylated form of CMP has been shown to exhibit antibacterial activity. The aim of this study was to use matrix assisted laser desorption/ionization post source decay mass spectrometry (MALDI-PSD-MS) to identify the phosphorylation sites in the CMP sequence. CMP was isolated from a chymosin digest of casein by HPLC and then digested with endoproteinase Glu-C to generate peptides suitable for MALDI-PSD-MS analysis. This analysis showed that CMP is fully phosphorylated at Ser(149) and only partially phosphorylated at Ser(127.) Dehydroalanyl residues corresponding to the phosphoserines of CMP were detected upon MALDI-PSD-MS analysis suggesting that the phosphoryl bond in phosphoserine is very labile during PSD analysis such that the phosphoryl group may be lost before backbone fragmentation.

Susceptibility to trypsinolysis of esterified milk proteins

Methyl-, ethyl- and propyl-esters of beta-lactoglobulin, alpha-lactalbumin and beta-casein were prepared and then hydrolyzed with trypsin in various conditions. Resulting hydrolysates were analysed by SDS electrophoresis and RP-HPLC. The degree of hydrolysis of esterified samples was generally lower than those of the non-modified proteins. The highest degrees of hydrolysis were obtained at pH 7--8 with native and esterified protein samples. beta-Lactoglobulin propyl ester and beta-casein methyl ester yielded the lowest degrees of hydrolysis. Ethyl- and propyl-esters of beta-casein showed high resistance towards tryptic attack, even after 20 h of hydrolysis. SDS electrophoretic patterns of tryptic hydrolysates of native proteins showed bands corresponding to low molecular weights. Tryptic hydrolysates of esterified proteins showed bands with higher sizes. RP-HPLC profiles of tryptic hydrolysates of esterified samples showed peaks with longer elution times than those obtained with native proteins, indicating the presence of more hydrophobic peptide populations. A peptic pre-treatment improved tryptic action on esterified proteins. It resulted in a better resolution of RP-HPLC profiles and in a complete disappearance of the protein after 20 h tryptic hydrolysis.

Purification of novel peptide antibiotics from human milk

A strategy was established for the identification of novel antimicrobial peptides from human milk. For the generation of bioactive peptides human milk was acidified and proteolyzed with pepsin simulating the digest in infants stomachs. Separation of proteins and resulting fragments was performed by means of reversed-phase chromatography detecting the antimicrobial activity of each fraction using a sensitive radial diffusion assay. In order to avoid the purification of the known abundant antimicrobial milk protein lysozyme, it was identified in HPLC fractions by its enzymatic activity and by matrix-assisted laser desorption ionization-mass spectrometry (MALDI-MS). On condition that lysozyme was not detectable and antibacterial activity of HPLC fractions was caused by a peptide, which was confirmed by proteolytic cleavage leading to a loss of activity, further purification was performed by consecutive chromatographic steps guided by the antibacterial assay. Using this strategy, an as yet unknown casein fragment exhibiting antimicrobial activity was purified in addition to antimicrobial lactoferrin fragments. The new antimicrobial peptide resembles a proteolytic fragment of human casein-K (residues 63-117) and inhibits the growth of gram-positive, gram-negative bacteria, and yeasts. Our results confirm that antimicrobially-active peptides are liberated from human milk proteins during proteolytic hydrolysis and may play an important role in the host defense system of the newborn.

Effects of dietary protein types on immune responses and levels of infection with Eimeria vermiformis in mice

The present study reports the dietary effects of bovine alpha whey fraction, bovine casein and soy protein isolate on the immune responsiveness of C57BL/6J mice infected with Eimeria vermiformis. During the patent period, mice fed alpha whey fraction had significantly higher blood total white cell, CD4+ and CD8+ lymphocyte counts and higher Con A-stimulated IFN-gamma production by spleen cells than those fed other protein sources, but there was no significant difference in output of faecal oocysts. Casein-fed mice had significantly higher levels of Con A- stimulated IFN-gamma production and a lower output of faecal oocysts than soy-fed mice. The study demonstrated that dietary proteins have different impacts on immune responsiveness and level of parasitic infection in the gut; however, the mechanisms affecting level of infection are not clear. These effects appeared not to be solely related to nutritional properties of the diets. Further research into the underlying immune mechanisms and possible direct interactions between bioactive proteins and the parasite E. vermiformis should be fruitful.

Biological activities of bovine glycomacropeptide

Biological activity of bovine kappa-caseino glycomacropeptide (GMP) has received much attention in recent years. Research has focused on the ability of GMP to bind cholera and Escherichia coli enterotoxins, inhibit bacterial and viral adhesion, suppress gastric secretions, promote bifidobacterial growth and modulate immune system responses. Of these, protection against toxins, bacteria, and viruses and modulation of the immune system are the most promising applications.

Opioid peptides encrypted in intact milk protein sequences

Opioid agonistic and antagonistic peptides which are inactive within the sequence of the precursor milk proteins can be released and thus activated by enzymatic proteolysis, for example during gastrointestinal digestion or during food processing. Activated opioid peptides are potential modulators of various regulatory processes in the body. Opioid peptides can interact with subepithelial opioid receptors or specific luminal binding sites in the intestinal tract. Furthermore, they may be absorbed and then reach endogenous opioid receptors.

Production of angiotensin-I-converting-enzyme-inhibitory peptides in fermented milks started by Lactobacillus delbrueckii subsp. bulgaricus SS1 and Lactococcus lactis subsp. cremoris FT4

Two fermented milks containing angiotensin-I-converting-enzyme (ACE)-inhibitory peptides were produced by using selected Lactobacillus delbrueckii subsp. bulgaricus SS1 and L. lactis subsp. cremoris FT4. The pH 4.6-soluble nitrogen fraction of the two fermented milks was fractionated by reversed-phase fast-protein liquid chromatography. The fractions which showed the highest ACE-inhibitory indexes were further purified, and the related peptides were sequenced by tandem fast atom bombardment-mass spectrometry. The most inhibitory fractions of the milk fermented by L. delbrueckii subsp. bulgaricus SS1 contained the sequences of beta-casein (beta-CN) fragment 6-14 (f6-14), f7-14, f73-82, f74-82, and f75-82. Those from the milk fermented by L. lactis subsp. cremoris FT4 contained the sequences of beta-CN f7-14, f47-52, and f169-175 and kappa-CN f155-160 and f152-160. Most of these sequences had features in common with other ACE-inhibitory peptides reported in the literature. In particular, the beta-CN f47-52 sequence had high homology with that of angiotensin-II. Some of these peptides were chemically synthesized. The 50% inhibitory concentrations (IC(50)s) of the crude purified fractions containing the peptide mixture were very low (8.0 to 11.2 mg/liter). When the synthesized peptides were used individually, the ACE-inhibitory activity was confirmed but the IC(50)s increased considerably. A strengthened inhibitory effect of the peptide mixtures with respect to the activity of individual peptides was presumed. Once generated, the inhibitory peptides were resistant to further proteolysis either during dairy processing or by trypsin and chymotrypsin.

Biochemical properties of regulatory peptides derived from milk proteins

Biologically active peptides derived from milk proteins are inactive within the sequence of the precursor proteins but can be released by enzymatic proteolysis. Based on structure-activity studies, peptides with a defined bioactivity show common structural features. Moreover, many milk protein-derived peptides reveal multifunctional bioactivities. Bioactive peptide fragments originating from milk proteins should be taken into account as potential modulators of various regulatory processes in the body. Opioid peptides are opioid receptor ligands with agonistic or antagonistic activities. Angiotensin converting enzyme (ACE) inhibitory peptides can exert an antihypertensive effect. Immunomodulating casein peptides have been found to stimulate the proliferation of human lymphocytes and the phagocytic activities of macrophages. Antimicrobial peptides have been shown to kill sensitive microorganisms. Antithrombotic peptides inhibit the fibrinogen binding to a specific receptor region on the platelet surface and also inhibit aggregation of platelets. Casein phosphopeptides can form soluble organophosphate salts and may function as carriers for different minerals, especially calcium. In relation to their mode of action, bioactive peptides may reach target sites (e.g., receptors, enzymes) at the luminal side of the intestinal tract or after absorption, in peripheral organs. The physiological significance of bioactive peptides as exogenous regulatory substances is not yet fully understood. Nevertheless, several bioactive peptides derived from milk proteins have been shown to exert beneficial physiological effects. Milk-derived peptides were already produced on an industrial scale and as a consequence these peptides have been considered for application both as dietary supplements in "functional foods" and as drugs.

Opioid peptides derived from hemoglobin: hemorphins

Investigation of hemoglobin peptic hydrolysate has revealed the presence of biologically active peptides with affinity for opioid receptors. Two peptides, VV-hemorphin-7 and LVV-hemorphin-7, were resolved by a combination of size exclusion and reversed phase HPLC. A new spectroscopic method based on the second order derivative spectra analysis of aromatic amino acids has been developed. This method allows qualitative and quantitative evaluation of hemorphins generated by peptic hemoglobin hydrolysis. Using this method, a kinetic study of hemorphins appearance has been undertaken. In this paper, we also evidenced the generation of VV-hemorphin-7 from globin by peritoneal macrophages. In regard to this result, the putative physiological role of hemorphins is discussed.

Bioactive milk peptides: a prospectus

Bioactive peptides have been identified within the amino acid sequences of native milk proteins. Hydrolytic reactions, such as those catalyzed by digestive enzymes, result in their release. These peptides directly influence numerous biological processes evoking behavioral, gastrointestinal, hormonal, immunological, neurological, and nutritional responses. The specific bioreactions associated with each physiological class have been well characterized. Herein, we review the scientific literature and attempt to stimulate consideration of the continued use of bioactive peptides and their expanded development as a commercial product. Several applications have already evolved. For example, phosphopeptides derived from casein fractions are currently used as both dietary and pharmaceutical supplements. Potentially, the addition of bioactive peptides to food products could improve consumer safety as a result of their antimicrobial properties. Lastly, bioactive peptides may function as health care products, providing therapeutic value for either treatment of infection or prevention of disease.

Detection of casein fragments in an invertebrate and in a vertebrate using in situ hybridization

Using a non-radioactive in situ hybridization procedure it has been demonstrated that both invertebrates such as the mollusc Mytilus galloprovincialis and lower vertebrates such as the fish Cyprinus carpio express bovine alphaS1- and kappa-casein homologous mRNAs. In particular, positive results were found in molluscan immunocytes, and in cells located in different fish tissues: intestine, endocrine pancreas and kidney. These findings suggest that the casein genes are highly conserved throughout evolution.

Hormones in Foods: Presence of Enterostatin-Like Immunoreactivities in Bovine Milk

Enterostatins, pentapeptides (Val-Pro-Asp-Pro-Arg [VPDPR], Val-Pro-Gly-Pro-Arg, Ala-Pro-Gly-Pro- Arg [APGPR], and others) derived from the amino terminus of procolipase, are endogenous to a variety of tissues and body fluids including brain, gut, blood, cerebrospinal fluid, and urine. The administration of exogenous peptides has been shown to elicit a variety of biologic activities, including a decrease in dietary fat preference and pancreatic insulin secretion. Since milk is a rich source of a variety of bioactive substances, especially peptides, we investigated the presence of enterostatin-like immunoreactivity in bovine milk. We measured enterostatins-APGPR and VPDPR-in milk from a herd of 19 cows randomly selected from the Louisiana State University Department of Dairy Science Research Herd in Baton Rouge; the results of this study show a mean peptide concentration in raw milk of 33.7 ± 2.9 ng/ml for APGPR and of 104.5 ± 16.3 ng/ml for VPDPR. A further chromatographic characterization of the nature of APGPR- and VPDPR-like immunoreactivities suggested the endogenous peptides share a common epitope with APGPR or VPDPR but are not APGPR or VPDPR. Unlike APGPR or VPDPR, the endogenous peptides were heat-labile and therefore their values were much lower in pasteurized milk.

Catalytic DNA- and RNA-hydrolyzing antibodies from milk of healthy human mothers

Various catalytically active antibodies (Abs), or abzymes, have been detected recently in the sera of patients with autoimmune pathologies, in whom their presence is probably associated with autoimmunization. Normal humans are generally not considered to have abzymes, since no obvious immunizing factors are present. Here is shown by different methods that IgG from the milk of normal females possesses both DNase and RNase activities. The activities were also present in the IgG F(ab')2 and Fab fragments. Affinity modification of IgG by the chemically reactive derivative of an oligonucleotide led to preferential modification of the L chain of IgG. After separation of the subunits by sodium dodecyl sulfate electrophoresis in a gel containing DNA, an in-gel assay showed DNase activity in the L chain. The L chain separated by affinity chromatography on DNA-cellulose was catalytically active. These findings speak in favor of the generation of catalytic Abs by the immune system of healthy mothers. It is known that the treatment of adults with DNases and RNases offers protection from viral and bacterial diseases. Since breast milk protects the infants from infections until the immune system is developed, this raises the possibility that catalytic Abs like nucleases, may possess a protective role.

Iron and oxidized beta-casein in the lavages of hyperoxic Fischer-344 rats

We reported previously that Fischer-344 (F344) rats were more susceptible to hyperoxic lung injury than were Sprague Dawley (SD) rats. In the present study we exposed adult male F344 and SD rats to >95% oxygen for up to 48 h, and measured lung wet-to-dry weight ratios and lavage protein concentrations as indices of lung injury. In addition, we measured nonheme iron contents in the lung subcellular fractions and in bronchoalveolar lavages (BAL), and we derivatized samples from the subcellular compartments and lavages with 2,4-dinitrophenylhydrazine (DNPH), separated the proteins electrophoretically, and detected DNPH-derivatized proteins by western blotting. After 48 h of hyperoxia, BAL protein and nonheme iron concentrations were higher in F344 rats than in SD rats (2.17+/-0.77 versus 0.17+/-0.17 mg/ml, and 1.61+/-0.45 versus 0.45+/-0.18 nmol/ml, respectively, both P<0.05). In addition, two DNPH-reactive proteins of about 40 and 120 kDa were identified in the lavage fluids of hyperoxic F-344 rats that were not observed similarly in hyperoxic SD rats or in air-breathing rats of either strain. N-terminal amino acid sequences of the two DNPH-reactive proteins 100% identical over 16 residues to rat beta-casein, which is a potent neutrophil chemotaxin, and has been reported to be a product of cytotoxic T-lymphocytes. There were no significant alterations in iron contents in lung subcellular fractions in either strain of rat as a consequence of hyperoxia-exposure, nor were there any significant alterations in DNPH-reactive carbonyls, as determined by western blotting. These data suggest that increased iron concentrations in the airspaces reflect altered iron homeostasis, which may contribute to the greater susceptibility of F344 rats than SD rats to hyperoxic lung injury. The identification of oxidized beta-casein in the BAL of the hyperoxic F344 rats suggests a role for cytotoxic T-lymphocytes in hyperoxic lung inflammation and injury, although the nature of this possible involvement is not known at this time.

DNA-hydrolyzing activity of the light chain of IgG antibodies from milk of healthy human mothers

Various catalytically active antibodies or abzymes have been detected recently in the sera of patients with several autoimmune pathologies, where their presence is most probably associated with autoimmunization. Normal humans are generally considered to have no abzymes, since no obvious immunizing factors are present. Recently we have shown that IgG (its Fab and F(ab)2 fragments) from the milk of normal humans possesses DNase activity. Here we demonstrate for the first time that the light chain of IgG catalyzes the reaction of DNA hydrolysis. These findings speak in favor of the generation of abzymes in the tissue of healthy mothers, and since a mother's breast milk protects her infant from infections until the immune system is developed, they raise the possibility that these abzymes may contribute to this protective role.

Apoptosis in human leukemic cells induced by lactoferricin, a bovine milk protein-derived peptide: involvement of reactive oxygen species

We examined the activity of bovine lactoferricin (Lfcin-B), a peptide derived from a bovine milk protein lactoferrin (LF-B), to induce apoptosis in THP-1 human monocytic leukemic cells. Treatment with Lfcin-B at up to 50 micrograms/ml induced cell death in THP-1 cells in dose- and time-dependent manner, showing apparent morphological changes, hypodiploid forms of genomic DNA and apoptotic DNA fragmentation, whereas LF-B was inactive even at a high dose (500 micrograms/ml). The apoptosis-inducing effect of Lfcin-B increased with reduction of serum concentration, but was inhibited by addition of Zn2+, a inhibitor of Ca2+/Mg(2+)-dependent endonucleases in a dose-dependent manner. Furthermore, Lfcin-B-induced apoptosis in THP-1 cells was completely abolished by addition of antioxidants such as N-acetyl-L-cysteine (NAC) and glutathione (GSH), but not by various cytokines and mitogen which can activate monocytic cells. In addition, THP-1 cells treated with Lfcin-B, but not LF-B, showed high levels of intracellular reactive oxygen species (ROS) from the early period (20 min) of Lfcin-B treatment. And the production of ROS by Lfcin-B was dependent upon the dose of Lfcin-B added. These results suggested that Lfcin-B, a LF-B-derived peptide, but not LF-B itself, is able to induce apoptosis in THP-1 human monocytic tumor cells, and that its apoptosis-inducing activity is related to the pathway mediated by production of the intracellular ROS and activation of Ca2+/Mg(2+)-dependent endonucleases.

Plasminogen activation system in human milk

BACKGROUND

Plasmin is the major endogenous protease present in milk. The level of plasmin activity is controlled by the availability of the precursor plasminogen and by the levels of plasminogen activators and inhibitors. Recently, a differential distribution of tissue-type plasminogen activator (t-PA) and urokinase-type plasminogen activator (u-PA) has been demonstrated in bovine milk. To assess whether this distribution pattern is a general feature, the occurrence of components of the plasminogen activation system in different fractions of human milk was investigated.

METHODS

Milk samples were separated into the following fractions; milk fat, skim milk, and milk cells by centrifugation. The different fractions were detected for the presence of plasminogen and plasminogen activators by immunoblotting and zymography. The distribution of t-PA and u-PA was investigated by ligand binding analysis. t-PA-catalyzed plasminogen activation was examined by a coupled chromogenic assay.

RESULTS

A differential distribution of plasminogen, t-PA, and u-PA was found. Casein micelles were found to exhibit t-PA and plasminogen binding activity, whereas the u-PA receptor was identified as the u-PA binding component in the cell fraction. Furthermore, human casein enhanced t-PA-catalyzed plasminogen activation, comparable to the enhancing effect obtained with fibrinogen fragments.

CONCLUSION

The finding of a differential distribution of u-PA and t-PA in milk suggests that the two activators may have different physiological functions, which involve protection against invading microorganisms and maintenance of patency and fluidity in the ducts of mammary gland, respectively.

Biologically active factors in bovine milk and dairy byproducts: influence on cell culture

Substantial progress has been made in our knowledge of the biological properties of mammal milks. Many nutritional, biochemical, immunological, or other biological properties have been studied in mature or industrially processed bovine milk as well as in human milk and colostrum. This article is a critical review of selected publications covering (1) the use of bovine milk or dairy byproducts (processed acid and enzymatic whey fractions) as a serum substitute for cell cultures, (2) specific factors in bovine milk and industrially processed milk the affect cell proliferation, and (3) the known functional and biological roles of two whey proteins: beta-lactoglobulin and the PP3 component.

Physical mapping of the murine casein locus reveals the gene order as alpha-beta-gamma-epsilon-kappa

The murine casein locus has been characterized by long-range restriction mapping and the analysis of large fragment genomic clones. Cloned sequences from five mouse casein genes (alpha, beta, gamma, epsilon, kappa) were used to screen a murine (strain 129) genomic library in a bacterial artificial chromosome vector (BAC). Of the nine clones isolated, two contained three casein genes alpha, beta, gamma and gamma, epsilon, kappa, respectively. The following combinations were found in other clones: alpha + beta, beta + gamma; and gamma + epsilon. Thus, the gene order in the locus can be deduced to be alpha-beta-gamma-epsilon-kappa. This order was confirmed by restriction analysis of the clones. A contig map of the clones and flanking sequences has been established by characterizing seven BAC clones, which together span approximately 470 kb. Long-range restriction analysis of genomic DNA indicates that the murine casein locus is confined to a 250-kb partial Xho I fragment. The alpha and beta casein genes were shown to be arranged in a tail-to-tail orientation.

Role of the O-phosphoserine clusters in the interaction of the bovine milk alpha s1-, beta-, kappa-caseins and the PP3 component with immobilized iron (III) ions

alpha s1- and beta-Caseins have a sequence cluster -Ser(P)-Ser(P)-Ser(P)-Glu-Glu- which is not present in kappa-casein and the whey PP3 component. The affinity of these phosphoproteins for the iron(III)-iminodiacetic acid (IDA) complex immobilized on Sepharose was studied as a function of pH, urea concentration, calcium ion concentration, enzymatic dephosphorylation and temperature. The affinity of the three polyphosphorylated proteins (alpha s1- and beta-caseins, PP3) was similar. The sequence cluster was not a specific recognition pattern of the iron(III) ion. These three proteins presented a site of high affinity and a site of weak affinity. kappa-Casein, which had only one Ser(P) residue, presented only the site of weak affinity. Their primary site which was absent after dephosphorylation or calcium ion addition required the presence of at least two Ser(P) residues close in space. Their secondary site was sensitive to the presence of urea. It was sensitive to pH variation for PP3 and kappa-casein. The study of the affinity of a few free amino acids towards iron(III)-IDA showed that the secondary site involved tryptophan and tyrosine residues for alpha s1- and beta-caseins, histidine residues for PP3 and cysteine residues for kappa-casein.

Oxidation of bovine beta-casein by hypochlorite

We recently observed two 2,4-dinitrophenylhydrazine (DNPH)-reactive proteins of 40 and 120 kDa in the bronchoalveolar lavage fluids of rats exposed to >95% O(2) for 48 h. The N-terminal sequences of these proteins were both identical over 16 amino acids with rat beta-casein, which, in addition to its more common association with milk, is produced by cytotoxic T-lymphocytes, and has been found to have proinflammatory properties. Because of the inflammatory response that accompanies hyperoxic lung injury, we investigated the oxidation of bovine beta-casein by HOCl. Following exposure to HOCl at 4 degrees C for 15 min, derivatization with DNPH, washing, and digestion with trypsin, the resultant peptides were separated by reverse-phase HPLC. One peptide isolated from a peak absorbing at 365 nm was identified as AVP(Y*)PQR, corresponding to amino acids 177-183 of bovine beta-casein. Analysis of the peptide by both electrospray and matrix assisted laser desorption ionization (MALDI) mass spectrometry identified a molecular ion MH+ of 1008.5 Da, which represents an increase of 178 Da from the calculated monoisotopic MH+ of the unmodified peptide of 830.45 Da. Daughter ion spectra of the doubly charged parent ion of the peptide further support the oxidation of the tyrosine to the quinone methide, with subsequent conversion to the corresponding hydrazone with DNPH. A second pair of products were identified as arising from oxidation of Y(193) within the tryptic peptide constituted by amino acids 184-202, and the corresponding chymotryptic cleavage side product, 191-202. Exposure of beta-casein to increasing amounts of HOCl revealed that M and Y residues were the most susceptible, although bovine beta-casein contains no C, and a single W, which would not be detected by our methods. The approach described in the present report can be used to evaluate the contributions of distinct mechanisms of oxidation in other experimental or pathological models.

Presence of casein immunoreactive epitopes in molluscs, fish and frog

The presence of a group of peptides derived from milk proteins (caseins) was examined by immunocytochemistry in various tissues from invertebrates and lower vertebrates. Phagocytic hemocytes from different species of molluscs, and cells located in the intestine wall or in related glands of invertebrates and lower vertebrates showed immunoreactivity to antibodies to whole casein and related fragments. Several functional tests (cell migration, inhibition test, phagocytosis) using these peptides were performed on the mollusc hemocytes. Only ovine caseinoglycopeptide was able to increase the phagocytic activity of the hemocytes towards bacteria.

Modulation of immune responses by bovine beta-casein

The present reports the influence of bovine beta-casein on in vitro and in vivo immune responses. Bovine beta-casein showed an inhibitory effect on ovine neutrophil chemotaxis but had an enhancing effect on superoxide production by neutrophils. In response to mitogenic stimulation, the proliferative response of both T and B lymphocytes was significantly enhanced by beta-casein. While beta-casein had no significant effects on IFN gamma production by ovine blood lymphocytes, and TNF alpha production and MCH Class II antigen expression by ovine bronchoalveolar macrophages, it enhanced IL-1 beta production by the macrophages, beta-casein also had no influence on bovine NK cell activity against a virally-infected cell line. Interestingly, beta-casein was found to reduce the adjuvant effect of matrix immune stimulating complexes (ISCOM) on anti-ovalbumin antibody response in mice when given intramuscularly. Taken together, the results suggest that bovine beta-casein had selective modulating effects in vitro on both innate and adaptive immune responses in ruminants, whereas systemic administration of beta-casein, that might have a depressive effect on adjuvant activity, requires further study.

Kinetic of in vitro generation of some hemorphins: early release of LVV-hemorphin-7, precursor of VV-hemorphin-7

Bovine globin has been hydrolysed by pepsin to different degrees of hydrolysis. Analysis of the hydrolysates, by reversed-phase high-performance liquid chromatography (RP-HPLC), shows the release of LVV- and VV-hemorphin-7. LVV-hemorphin-7 was the first generated, at a degree of hydrolysis (DH), as low as 4%. In contrast, VV-hemorphin-7 was produced later. Our study clearly shows that VV-hemorphin-7 is issued directly from LVV-hemorphin-7, since this later completely disappeared during hydrolysis. This work allows us to suggest a possible pathway for in vivo hemorphins appearance.

Remodeling of mouse milk glycoconjugates by transgenic expression of a human glycosyltransferase

The mammary gland is a unique biosynthetic tissue that produces a variety of species-specific glycoconjugates, but the factors regulating the production of specific glycoconjugates are not well understood. To explore the underlying regulation, a fusion gene containing a cDNA encoding the human alpha 1,2-fucosyltransferase (alpha 1,2FT), which generates the H-blood group antigen, flanked by the murine whey acidic protein promoter and a polyadenylation signal, was introduced into mice. Milk samples from transgenic animals contained soluble forms of the alpha 1,2FT, as revealed by Western blots of milk samples using an anti-alpha 1,2FT antiserum and by the demonstration of alpha 1,2FT enzyme activity. Milk from transgenic animals also contained large quantities of 2'-fucosyllactose (Fuc alpha 1-2Gal beta 1-4Glc) and modified glycoproteins containing the H-antigen, whereas milk from control animals lacked these glycoconjugates. Expression levels of 2'-fucosyllactose were high in most animals and represented 1/3 to nearly 1/2 of the total milk oligosaccharides. These results demonstrate that heterologous transgenic expression of a glycosyltransferase can result in the expression of both the transgene and its secondary gene products and that the structures of milk oligosaccharides can be remodeled depending on expression of the appropriate enzyme. Furthermore, these results suggest that the lactating mammary gland may be a unique biosynthetic reactor for the production of biologically active oligosaccharides and glycoconjugates.

Casocidin-I: a casein-alpha s2 derived peptide exhibits antibacterial activity

Here we report the isolation and characterization of an antibacterial peptide from bovine milk inhibiting the growth of Escherichia coli, and Staphylococcus carnosus. The primary structure of the peptide was revealed as a 39-amino-acid-containing fragment of bovine alpha s2-casein (position 165-203) by means of Edman amino acid sequencing and mass spectrometry. Since human milk does not contain any casein-alpha s2, these findings could explain the different influence of human and bovine milk on the gastrointestinal flora of the suckling.

Apoptosis induced by a human milk protein

To the breast-fed infant, human milk is more than a source of nutrients; it furnishes a wide array of molecules that restrict microbes, such as antibodies, bactericidins, and inhibitors of bacterial adherence. However, it has rarely been considered that human milk may also contain substances bioactive toward host cells. While investigating the effect of human milk on bacterial adherence to a human lung cancer cell line, we were surprised to discover that the milk killed the cells. Analysis of this effect revealed that a component of milk in a particular physical state--multimeric alpha-lact-albumin--is a potent Ca(2+)-elevating and apoptosis-inducing agent with broad, yet selective, cytotoxic activity. Multimeric alpha-lactalbumin killed all transformed, embryonic, and lymphoid cells tested but spared mature epithelial elements. These findings raise the possibility that milk contributes to mucosal immunity not only by furnishing antimicrobial molecules but also by policing the function of lymphocytes and epithelium. Finally, analysis of the mechanism by which multimeric alpha-lactalbumin induces apoptosis in transformed epithelial cells could lead to the design of antitumor agents.

Inhibition of mitogen-induced proliferative responses of lymphocytes by bovine kappa-caseinoglycopeptides having different carbohydrate chains

Bovine kappa-caseinoglycopeptides (i.e. residues 106-169, CGP) were prepared from kappa-casein digested with rennin and a commercial whey protein concentrate. CGP from whey protein concentrate was further divided into seven CGP fractions having different carbohydrate compositions using FPLC. Unfractionated CGP inhibited lipopolysaccharide (LPS)- and phytohaemagglutinin (PHA)-induced proliferative responses of mouse spleen cells and rabbit Peyer's patch cells. The unfractionated CGP also inhibited antibody responses to sheep red blood cells in mouse spleen cell cultures. However, seven CGP fractions having zero to five N-acetylneuraminic acid (NANA) residues had different inhibitory effects on both LPS- and PHA-induced proliferative responses of mouse spleen cells. The inhibitory effect on PHA-induced proliferative responses increased with increasing numbers of NANA residues, whereas that on LPS-induced proliferation was highest with the CGP fraction having two NANA residues. Both inhibitory effects decreased significantly after neuraminidase or chymotrypsin digestion. These findings indicate that both the carbohydrate (particularly the NANA residues) and the polypeptide portions are essential for inhibitory effects on LPS- and PHA-induced proliferative responses of mouse spleen cells.

Inhibition of proliferative responses of mouse spleen lymphocytes and rabbit Peyer's patch cells by bovine milk caseins and their digests

The modulating effect of bovine milk casein components and their digests on the proliferative responses of mouse spleen lymphocytes and rabbit Peyer's patch cells induced or not induced by mitogens has been studied with a colorimetric assay using 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide. All the casein components and their digests tested had little mitogenic effect on the proliferative responses of mouse spleen lymphocytes and rabbit Peyer's patch cells. Intact kappa-casein significantly inhibited the proliferative responses of mouse spleen lymphocytes and Peyer's patch cells induced by mitogens such as lipopolysaccharide from Salmonella typhimurium, concanavalin A, phytohaemagglutinin and pokeweed mitogen. In contrast, intact alpha s1-casein and beta-casein had little effect. kappa-Casein had an inhibitory effect after digestion by pancreatin or trypsin, but not after pepsin or chymotrypsin digestion. Both pancreatin and trypsin digests of alpha s1-casein and beta-casein significantly inhibited the proliferative responses of mouse spleen lymphocytes and rabbit Peyer's patch cells induced by mitogens, whereas pepsin and chymotrypsin digests of both caseins were without effect. Moreover, the trypsin digest of each casein component had an inhibitory effect on mouse spleen lymphocyte proliferation in the absence of mitogen. Since trypsin is a major proteinase in pancreatin, the substrate specificity of trypsin seems to be important for the formation of the inhibitory peptides from casein components. These observations suggest that intact kappa-casein and some peptides formed from milk casein components by the action of trypsin may suppress the immune responsiveness of neonates.

Peptic hemoglobin hydrolysis in an ultrafiltration reactor at pilot plant scale generates opioid peptides

Two hemorphins, peptides with opioid activity, have been isolated from a pepsin hydrolysate of bovine hemoglobin, by use of gel permeation (GP) and reverse phase (RP) high-performance liquid chromatography (HPLC). Their primary structure and accurate molecular weights, determined by amino acid analysis and fast atom bombardment (FAB) mass spectrometry, were identical to fragments 31-40 (LVV-hemorphin-7) and 32-40 (VV-hemorphin 7) of the beta-chain of bovine hemoglobin. Two other peptides, 34-40 (hemorphin-7) and 34-41 (hemorphin-8) of the beta-chain of bovine hemoglobin, have been synthesized and studied. The opioid potency of these peptides, exhibited by the use of electrically stimulated muscle of isolated guinea pig ileum (GPI), were significant and comparable with some others previously described. Studies of opioid activities and primary structure of hemorphins led us to postulate the important role of arginine and phenylalanine in opioid potency.

Bioactive peptides derived from milk proteins. Structural, physiological and analytical aspects

The primary function of dietary proteins is to supply the body adequately with indispensable amino acids and organic nitrogen. Little attention has been paid up to date to milk proteins, in particular caseins, that are currently the main source of biologically active peptides, although other animal as well as vegetable proteins are known to contain potentially bioactive sequences. Such regulatory peptides can be released by enzymatic proteolysis of caseins in vitro and in vivo and may act as potential physiological modulators of metabolism during the intestinal digestion of the diet. It has been proved that bioactive peptides derived from caseins, such as beta-casomorphins and phosphopeptides, can be released during gastrointestinal passage. It is also evident that peptides originating from food proteins should be taken into account as potential modulators of various regulatory processes in the body. The possible regulatory effects concern nutrient uptake (phosphopeptides, casomorphins), postprandial hormone secretion (casomorphins), immune defense (immunopeptides, casokinins, casomorphins) and neuroendocrine information transfer (casokinins). The advances in the research field of bioactive peptides are driven by a molecular understanding of biological processes, and analytical techniques are a critical component of this understanding. Different up-to-date methods, including peptide synthesis and immunochemistry, have been applied to the chemical characterization of bioactive peptides. Especially casein derived peptides have already found interesting applications, both as dietary supplements (phosphopeptides) and as pharmaceutical preparations (phosphopeptides, beta-casomorphins). The question of 'what kinds of bioactive peptides are beneficial and desirable as food constituents or as drugs' should be always carefully examined. However, the possibilities for the design of dietary products and 'natural' drugs look promising.

The effect of milk and casein proteins on the adherence of Streptococcus mutans to saliva-coated hydroxyapatite

Experiments sought to determine the nature of the binding of milk proteins to hydroxyapatite (HA) and to saliva-coated hydroxyapatite (sHA), and to determine the effect of milk and casein on the adherence of Streptococcus mutans GS-5 to sHA. The binding of radiolabelled alpha-casein to HA was reduced when incubated simultaneously with parotid saliva, and enhanced in the presence of milk. The binding of beta- and kappa-casein to HA was unaffected by the presence of parotid saliva and enhanced by the presence of milk. The in vitro bacterial adherence of Strep. mutans GS-5 to sHA beads was reduced when beads were coated with milk instead of buffer, or when bacteria were added to sHA in the presence of milk instead of buffer. Casein proteins (alpha, beta, kappa) added to sHA simultaneously with bacteria inhibited the adherence of Strep. mutans GS-5 to sHA. kappa-Casein, when bound to sHA, inhibited streptococcal adherence to sHA; alpha- and beta-casein, when bound to sHA, had no effect on streptococcal adherence. Fractionation of kappa-casein by anion-exchange chromatography revealed the anti-adherence activity of kappa-casein was mediated primarily by a 40,000 mol. wt. glycoprotein-containing fraction. These data show that milk, particularly kappa-casein fractions, can modulate the adherence of Strep. mutans GS-5 to SHA surfaces in vitro.

Characterization of the oligopeptides of Parmigiano-Reggiano cheese soluble in 120 g trichloroacetic acid/l

The non-protein nitrogen (NPN) of samples of Parmigiano-Reggiano cheese ripened for 6 and 15 months was fractionated by ion-exchange chromatography on a Cu(2+)-Chelex column to separate oligopeptides from free amino acids. Peptide components were isolated by reversed-phase HPLC and identified by fast atom bombardment-mass spectrometry (FAB-MS). Only the NPN fraction of 6 month old cheese samples contained enough peptides to be further characterized. On the basis of FAB-MNS spectral results, 39 oligopeptides were identified, the main components being phosphopeptides. Two sets of both intact and partly dephosphorylated peptides, accounting for a total of 19 phosphopeptides, were formed by the hydrolysis of beta-casein and belonged to regions 1-20 and 6-28 of beta-casein. The formation and potential role of these peptides in cheese is discussed.

The plasminogen activation system in bovine milk: differential localization of tissue-type plasminogen activator and urokinase in milk fractions is caused by binding to casein and urokinase receptor

We have analyzed the occurrence of components of the plasminogen activation system in bovine milk. Zymographic analyses showed that tissue-type plasminogen activator (t-PA) occurred in association with casein micelles, partially as a complex with type-1 plasminogen activator inhibitor (PAI-1), whereas urokinase-type plasminogen activator (u-PA) was confined to milk leukocytes. Whey contained a component with a plasminogen dependent proteolytic activity which was shown to be plasma prekallikrein (PPK). The u-PA in the milk leukocytes was shown to be bound to urokinase receptor (u-PAR). A purification to near-homogeneity of the bovine u-PAR was undertaken. Investigating the novel t-PA binding to casein micelles by ligand blotting and Sepharose immobilized casein, multimeric forms of kappa-casein and dimeric alpha s2-casein were identified as t-PA binding components. The kappa-casein gene and the fibrinogen gene are believed to have evolved from a common ancestor. Thus, the recent finding that casein enhances t-PA catalyzed plasminogen activation (Marcus, G., Hitt, S., Harvey, S.R. and Tritsch, G.L. (1993) Fibrinolysis 7, 229-236), and the observed t-PA/casein binding suggests that the casein micelle, which also contains plasminogen, may serve as a matrix for t-PA-catalyzed plasminogen activation in milk.

A cell culture model to identify biologically active peptides generated by bacterial hydrolysis of casein

Consumption of fermented dairy foods has been linked to reduced incidence of colon cancer in population groups. Recently, biologically active compounds have been isolated from these products. Bacterial proteinases, produced by dairy starter cultures, generate a variety of peptides from casein. Some of these casein-derived peptides are likely to alter intestinal cell kinetics. Effects on colon cell kinetics because of the presence of casein-derived peptides may be a mechanism through which fermented dairy foods reduce the risk of colon cancer. We have used two intestinal cell lines (IEC-6 cells, derived from normal rat intestine, and Caco-2 cells, derived from human colon adenocarcinoma) to identify casein peptides that affect intestinal cell kinetics. Cell culture media containing casein were inoculated with three commercial starter cultures and incubated for 4, 8, or 24 h. The bacteria-conditioned media were then filter-sterilized and incubated with the intestinal cells for 6 or 24 h. Rates of [3H]thymidine incorporation and cell cycle kinetics determined by flow cytometry were affected by the culture-modified media in both cell lines. The IEC-6 cells tended to reduce, and Caco-2 cells to increase, rates of cell division after exposure to the media. Intestinal cell response varied among the starter cultures. The results support the use of intestinal cell cultures to identify casein peptides generated by dairy starter cultures, which affect intestinal cell kinetics.

Conserved phosphorylation of serines in the Ser-X-Glu/Ser(P) sequences of the vitamin K-dependent matrix Gla protein from shark, lamb, rat, cow, and human

The present studies demonstrate that matrix Gla protein (MGP), a 10-kDa vitamin K-dependent protein, is phosphorylated at 3 serine residues near its N-terminus. Phosphoserine was identified at residues 3, 6, and 9 of bovine, human, rat, and lamb MGP by N-terminal protein sequencing. All 3 modified serines are in tandemly repeated Ser-X-Glu sequences. Two of the serines phosphorylated in shark MGP, residues 2 and 5, also have glutamate residues in the n + 2 position in tandemly repeated Ser-X-Glu sequences, whereas the third, shark residue 3, would acquire an acidic phosphoserine in the n + 2 position upon phosphorylation of serine 5. The recognition motif found for MGP phosphorylation, Ser-X-Glu/Ser(P), has been seen previously in milk caseins, salivary proteins, and a number of regulatory peptides. A review of the literature has revealed an intriguing dichotomy in the extent of serine phosphorylation among secreted proteins that are phosphorylated at Ser-X-Glu/Ser(P) sequences. Those phosphoproteins secreted into milk or saliva are fully phosphorylated at each target serine, whereas phosphoproteins secreted into the extracellular environment of cells are partially phosphorylated at target serine residues, as we show here for MGP and others have shown for regulatory peptides and the insulin-like growth factor binding protein 1. We propose that the extent of serine phosphorylation regulates the activity of proteins secreted into the extracellular environment of cells, and that partial phosphorylation can therefore be explained by the need to ensure that the phosphoprotein be poised to gain or lose activity with regulated changes in phosphorylation status.(ABSTRACT TRUNCATED AT 250 WORDS)

Specific binding sites on human phagocytic blood cells for Gly-Leu-Phe and Val-Glu-Pro-Ile-Pro-Tyr, immunostimulating peptides from human milk proteins

Two immunostimulating peptides were isolated from human milk proteins by enzymatic digestion, the tripeptide GLF and the hexapeptide VEPIPY. These peptides increased the phagocytosis of human and murine macrophages and protected mice against Klebsiella pneumoniae infection. The present study showed that this activity may be correlated to the presence of specific binding sites on human blood phagocytic cells. The receptor molecules implicated were different for the two peptides. [3H]GLF specifically bound to PMNL and monocytes, whereas [3H]VEPIPY only bound to monocytes. The leukemic promyelocytic cell line HL-60 differentiated into granulocytes or into macrophages (depending on inducer used) coroborated these results. Specific binding of [3H]GLF on plasma membrane preparations of human PMNL (20 degrees C) was saturable and Scatchard analysis indicated two classes of binding sites: high-affinity sites of Kd 2.3 +/- 1.0 nM and Bm 60 +/- 9 fmol/mg protein and low-affinity sites of Kd 26.0 +/- 3.5 nM and Bm 208 +/- 45 fmol/mg protein. [3H]GLF binding was inhibited in a concentration-dependent manner by various analogous peptides, such as LLF, GLY, LLY and RGDGLF, but not by RGD, RGDS, VEPIPY and the chemotactic peptide f-Met-Leu-Phe (f-MLF). Only at high concentrations the direct analog MLF competed with labeled GLF. An important inhibitory effect was also observed with C1q component of the complement whereas C3 and BSA were uneffective. Specific binding of [3H]VEPIPY on monocyte membranes (20 degrees C) was saturable and Scatchard analysis was consistent with one class of binding sites of Kd 3.7 +/- 0.3 nM and Bm 150 +/- 6 fmol/mg protein.

Isolation and characterization of two opioid peptides from a bovine hemoglobin peptic hydrolysate

Two opioid peptides were isolated from a bovine hemoglobin hydrolysate, by use of gel permeation (GP) and reverse phase (RP) high performance liquid chromatography (HPLC). Their primary structure and accurate molecular weights, determined by amino acid analysis and fast atom bombardment (FAB) mass spectrometry, were identical to fragments 31-40 (LVV-hemorphin-7) and 32-40 (VV-hemorphin 7) of the beta-chain of bovine hemoglobin. The same fragments occur in human hemoglobin in positions 32-41 and 33-41 of the beta-chain, respectively. The opioid potency of these peptides, exhibited by use of electrically stimulated muscle of isolated guinea-pig ileum (GPI), were significant and comparable with some others previously described. In addition, the location of the two opioid peptides, VV-hemorphin-7 and LVV-hemorphin-7, revealed the existence of a "strategic zone" both in the bovine and human beta-chains of hemoglobin.

Effects of tripeptides derived from milk proteins on polymorphonuclear oxidative and phosphoinositide metabolisms

The tripeptide GLF (glycyl-leucyl-phenylalanine) was isolated from human milk proteins. This peptide increased phagocytosis by human and murine macrophages and protected mice against Klebsiella pneumoniae infection. Specific binding sites on human polymorphonuclear leukocytes (PMNs) have been demonstrated recently. The aim of the present research was to study the action of this peptide on rat and human PMN oxidative burst and to investigate the consequences of cell stimulation on polyphosphoinositide hydrolysis. A biphasic stimulating concentration-dependent effect of GLF on PMN chemiluminescence and superoxide anion generation was demonstrated. One of the peaks of the oxidative response occurred around 10(-9) M, which correlates with the Kd of high affinity receptors of GLF. The other maximum, around 10(-4) M, might be due to the hydrophobic nature of the tripeptide. O2- generation mimicked the phorbol myristate acetate response: after a lag period of 2-5 min, O2- release gradually increased for 10-15 min until a plateau was reached. Furthermore, GLF enhanced phosphoinositide breakdown with maximal IP3 production at 10(-7) M. Various analogs of GLF were synthesized in order to define the relative importance of the different amino acids and their position in the tripeptide molecule: glycyl-phenylalanine-leucine was devoid of biological properties but enhanced the activity of GLF on the metabolic burst at high concentrations; peptides leucyl-leucyl-phenylalanine and leucyl-leucyl-tyrosine, which displaced GLF from its specific membrane receptors, exerted stimulating effects on PMN oxidative and phosphoinositide metabolisms. It is quite conceivable that these short peptides, which may be generated in the newborn during digestion and which are able to stimulate phagocytic cells, are implicated in the defense of the neonate immature organism against infection.