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PubMed1999

Alternative nonallelic deletion is constitutive of ruminant alpha(s1)-casein.

Multiple forms of alpha(s1)-casein were identified in the four major ruminant species by structural characterization of the protein fraction. While alpha(s1)-casein phenotypes were constituted by a mixture of at least seven molecular forms in ovine and caprine species, there were only two forms in bovine and water buffalo species. In ovine and caprine forms the main component corresponded to the 199-residue-long form, and the deleted proteins differed from the complete one by the absence of peptides 141-148, 110-117, or Gln78, or a combination of such deletions. The deleted segments corresponded to the sequence regions encoded by exons 13 and 16, and by the first triplet of exon 11 (CAG), suggesting that the occurrence of the short protein forms is due to alternative skipping, as previously demonstrated for some caprine and ovine phenotypes. The alternative deletion of Gln78 in alpha(s1)-casein, the only form common to the milk of all the species examined and located in a sequence region joining the polar phosphorylation cluster and the hydrophobic C-terminal domain of the protein, may play a functional role in the stabilization of the milk micelle structure.

Alleles↗

PubMed2003

Biochemical and pharmacological aspects of two bradykinin-potentiating peptides obtained from tryptic hydrolysis of casein.

Peptides that display bradykinin-potentiating activity have been obtained from a number of distinct sources, such as snake venoms, fibrinogen, and casein. This paper describes the characterization of two new peptides generated by tryptic hydrolysis of casein. No homology was found with other known vasoactive or vasopotentiating peptides, especially by the lack of Ile-Pro-Pro motif. The peptides EMPFPK and YPVEPFTE, corresponding to the gamma casein sequence (108-113 and 114-121, respectively), displayed a selective potentiating activity on isolated guinea pig ileum for bradykinin. Besides, the octapeptide YPVEPFTE showed an in vitro competitive inhibitor effect on angiotensin-converting enzyme and thimet oligopeptidase and presented an opiate-like activity, increasing two times the latence time in the hot-plate assay. The results suggest that the isolated bioactive peptides act on conversion and/or inactivation of endogenous peptides by enzymes such as angiotensin-converting enzyme and thimet oligopeptidase by modifying several systemic responses such as blood-pressure regulation and in pain response.

Amino Acid Sequence↗

PubMed2003

The effect of graded levels of dietary casein, with or without methionine supplementation, on glutathione concentration in unstressed and endotoxin-treated rats.

Glutathione (GSH) concentration was measured in rats fed either graded levels of dietary casein (experiment 1; 180 g, 120 g, 80 g, or 60 g protein/kg diet) or graded levels of dietary casein, supplemented with methionine to equalize dietary sulfur amino acid content to that seen in an 180 g/kg casein diet supplemented with 0.3 g L-methionine/kg diet (experiment 2; 180 g protein +0.3 g L-methionine, 80 g protein +6.70 g L-methionine, or 60 g protein +7.45 g L-methionine/kg diet). Rats were given an inflammatory challenge by intraperitoneal injection of endotoxin (lipopolysaccharide from Escherichia coli), and were compared with ad libitum and pair-fed controls. Glutathione concentration in various organs (liver, lung, spleen, and thymus) decreased in animals fed the low-protein diets (80 g or 60 g/kg diet). Addition of the sulfur amino acid, methionine, to the low-protein diets restored glutathione concentrations in animals fed ad libitum and prevented the fall in GSH concentration, which occurred in lung, spleen, and thymus in response to the endotoxin. Despite the similarity in the amount of sulfur amino acid consumed between the groups fed the 180 g protein +0.3 g L-methionine and the 60 g protein +7.45 g L-methionine/kg diet, in experiment 2, hepatic GSH concentration significantly increased in the latter group, in animals fed ad libitum and in the endotoxin-treated animals, but not in the pair-fed controls.

Amino Acids, Sulfur↗

PubMed2006

Evidence of a novel biomarker, alphas1-Casein, a milk protein, in benign prostate hyperplasia.

Benign prostate hyperplasia (BPH) is a common disease in elderly men. Although it is a non-malignant disease, it has a significant detrimental impact on the quality of life in patients with late-stage disease. Owing to the lack of specific markers, diagnosis of early-stage BPH has been proven unsuccessful. Recently, using two-dimensional electrophoresis, we identified a group of prostatic secretory proteins that are specifically produced by BPH cells (Xu et al., Electrophoresis 2003; 24: 1311). In this study, we investigated the potential diagnostic value of one of the secretory proteins, alphas1-Casein, in BPH by inmmunohistological staining of normal, BPH and prostate cancer tissues. We found that 90% (20 out of 22) of BPH tissues showed moderate to strong alphas1-Casein protein expression whereas none of the normal tissues (0 out of 10) and less than 10% of the prostate cancer tissues (3 out of 30) showed similar staining intensity. Our results suggest that alphas1-Casein may be a potential biomarker for early identification of BPH patients.

Adenocarcinoma↗

PubMed2001

Cation-dependent structural features of beta-casein-(1-25).

Complete sequence-specific, proton-resonance assignments have been determined for the calcium phosphate-stabilizing tryptic peptide beta-casein-(1-25) containing the phosphorylated sequence motif Ser(P)(17)-Ser(P)-Ser(P)-Glu-Glu(21). Spectra of the peptide have been recorded, in separate experiments, in the presence of excess ammonium ions, sodium ions and calcium ions, and of the dephosphorylated peptide in the presence of excess sodium ions. We observed significant changes to chemical shifts for backbone and side-chain resonances that were dependent upon the nature of the cation present. Medium-range nuclear Overhauser effect (nOe) enhancements, characteristic of small structured regions in the peptide, were observed and also found to be cation dependent. The secondary structure of the peptide was characterized by sequential and medium-range (i, i+2/3/4, which denotes an interaction between residue i and residue i+2, i+3 or i+4 in the peptide) nOe connectivities, and Halpha chemical shifts. Four structured regions were identified in the calcium-bound peptide: residues Arg(1) to Glu(4) were involved in a loop-type structure, and residues Val(8) to Glu(11), Ser(P)(17) to Glu(20) and Glu(21) to Thr(24) were implicated in beta-turn conformations. Comparison of the patterns of medium-range nOe connectivities in beta-casein-(1-25) with those in alpha(S1)-casein-(59-79) suggest that the two peptides have distinctly different conformations in the presence of calcium ions, despite having a high degree of sequential and functional similarity.

Amino Acid Sequence↗

PubMed1975

Multiple protein kinases from human lymphocytes. Identification enzymes phosphorylating exogenous histon and casein.

1. Cell-free lysates of human peripheral blood lymphocytes contained two casein kinase activities and two histone kinase activities, which could be separated by chromatography on DEAE-Sephadex. 2. Neither of the casein kinase activities were stimulated by cyclic AMP. The major activity was eluted from DEAE-Sephadex between 0.4 and 0.45M-KCl, had a molecular weight of approx. 130,000 (sucrose density gradients) and was stimulated by KCl (maximum 150mM). It also formed higher-molecular-weight aggregates when centrifuged in sucrose gradients containing 150mM-KCl. The minor activity was not retained by DEAE-Sephadex, had a molecular weight of approx. 50,000 and was not stimulated by KCl. 3. The major histone kinase activity was stimulated by cyclic AMP and was eluted from the DEAE-Sephadex column between 0.05 and 0.2M-KCl. The other activity was not stimulated by cyclic AMP and was insensitive to the rabbit muscle protein kinase inhibitor. 4. Evidence was obtained suggesting that the lymphocyte casein kinases were located primarily in the nuclei.

Caseins↗

PubMed1985

A 1H-n.m.r. study of casein micelles.

The 1H-n.m.r. spectrum of casein micelles consists of a small number of moderately sharp (linewidth approx. 60 Hz) resonances superimposed on the envelope of very broad lines expected for particles of this size. These sharp lines resemble, in chemical shift and relative intensity, the spectrum of the isolated 'macropeptide' released from the micelles by treatment with chymosin. The sharp lines in the casein micelle spectrum are further sharpened by addition of chymosin and broadened markedly by addition of ethanol. These observations are consistent with the proposal that the 'macropeptide' (the C-terminal 64 residues of K-casein) forms flexible 'hairs' on the surface of the micelles.

Animals↗

PubMed1987

Peptide substrates for chymosin (rennin). Interaction sites in kappa-casein-related sequences located outside the (103-108)-hexapeptide region that fits into the enzyme's active-site cleft.

The role of individual amino acid residues in the 98-102 and 111-112 regions of bovine kappa-casein in its interaction with the milk-clotting enzyme chymosin (rennin) was investigated. to this end the tryptic 98-112 fragment of kappa-casein was modified in its N- and/or C-terminal part by chemical (guanidation, ethoxyformylation, repeated Edman degradation) and enzymic (carboxypeptidase) treatments. Further, use was made of short synthetic kappa-casein analogues in which His-102 had been replaced by Pro or Lys. All peptides and their derivatives were tested comparatively at various pH values for their ability to act as chymosin substrates via specific cleavage of the peptide bond at position 105-106. The results indicate that in the alternating 98-102 sequence (His-Pro-His-Pro-His) the His as well as the Pro residues contribute to the substrate activity with no predominant role of any one of these groups. Another interaction site is formed by the Lys residue at position 111 of the substrate. A model of the enzyme-substrate complex is proposed. Herein the 103-108 fragment of the substrate, to be accommodated within the enzyme's active-site cleft, is brought into position by electrostatic binding (via His-98, His-100, His-102 and Lys-111) near the entrance of the cleft. These interactions are strongly supported by Pro residues at positions 99, 101, 109 and 110 of the substrate, which act as stabilizers of the proper conformation of the substrate in the enzyme-substrate complex.

Amino Acids↗

PubMed1989

Kinetics of inhibition by 5,6-dichloro-1-beta-D-ribofuranosylbenzimidazole on calf thymus casein kinase II.

The adenosine analogue 5,6-dichloro-1-beta-D-ribofuranosylbenzimidazole (DRB) is a specific inhibitor for RNA polymerase II transcription in vivo and in vitro [Tamm + Sehgal (1978) Adv. Virus Res. 22, 187-258; Zandomeni & Weinmann (1984) J. Biol. Chem. 259, 14804-14811]. The effect on RNA polymerase II-specific transcription seems to be mediated by its inhibition of nuclear casein kinase II [Zandomeni, Carrera-Zandomeni, Shugar & Weinmann (1986) J. Biol. Chem. 261, 3414-3419]. Inhibition studies indicated that DRB acted as a mixed-type inhibitor with respect to casein and as a competitive inhibitor with respect to the nucleotide phosphate donor substrates. The DRB inhibition constant is 7 microM for the calf thymus casein kinase II, with regard to both ATP and GTP.

Animals↗

PubMed1993

Phosphorylation by casein kinase II affects the interaction of caldesmon with smooth muscle myosin and tropomyosin.

Smooth muscle caldesmon was phosphorylated by casein kinase II, and the effects of phosphorylation on the interaction of caldesmon and its chymotryptic peptides with myosin and tropomyosin were investigated. The N-terminal chymotryptic peptide of caldesmon of molecular mass 27 kDa interacted with myosin. Phosphorylation of Ser-73 catalysed by casein kinase II resulted in a 2-fold decrease in the affinity of the native caldesmon (or its 27 kDa N-terminal peptide) for smooth muscle myosin. At low ionic strength, caldesmon and its N-terminal peptides of molecular masses 25 and 27 kDa were retarded on a column of immobilized tropomyosin. Phosphorylation of Ser-73 led to a 2-4-fold decrease in the affinity of caldesmon (or its N-terminal peptides) for tropomyosin. Thus phosphorylation of Ser-73 catalysed by casein kinase II affects the interaction of caldesmon with both smooth muscle myosin and tropomyosin.

Animals↗

PubMed1994

Full activation of a nuclear species of protein phosphatase-1 by phosphorylation with protein kinase A and casein kinase-2.

Bovine thymus nuclei contain a species of protein phosphatase-1 (PP-1N alpha) that can be partially activated by phosphorylation of an associated inhibitory polypeptide, NIPP-1, with protein kinase A [Beullens, Van Eynde, Bollen and Stalmans (1993) J. Biol. Chem. 268, 13172-13177]. Here it is shown that PP-1N alpha can also be activated 4-fold by phosphorylation of NIPP-1 with casein kinase-2. The effects of protein kinase A and casein kinase-2 were additive, yielding an enzyme with an activity close to that of the free catalytic subunit. Casein kinase-2 introduced up to 1.2 phosphate groups into purified NIPP-1 on serine and threonine residues. This phosphorylation was associated with a 14-fold increase in the concentration of NIPP-1 required for 50% inhibition of the type-1 catalytic subunit. The kinase-mediated inactivation of NIPP-1 could be reversed by incubation with the catalytic subunit of protein phosphatase-2A.

Animals↗

PubMed1994

Transforming growth factor-beta 1 inhibits casein secretion from differentiating mammary-gland explants but not from lactating mammary cells.

Transforming growth factor-beta (TGF beta) is important in the maturation and function of the mammary gland and is present in milk. We have examined whether, in addition to inhibiting lactogenesis, TGF beta exerts acute regulatory effects on lactating mammary cells. The isoform TGF beta 1 at 5 and 50 ng/ml suppressed the onset of lactation and the subsequent production of beta-casein by differentiating mouse mammary explants from pregnant mice. By contrast, it did not inhibit protein synthesis or secretion from acini isolated from lactating-mouse mammary gland or protein secretion from explants from lactating mice. These data indicate that TGF beta inhibits the onset of casein secretion, but is not an acute regulator of casein synthesis or secretion from differentiated lactating mammary cells.

Animals↗

PubMed1996

Characterization of the effects of Ca2+ depletion on the synthesis, phosphorylation and secretion of caseins in lactating mammary epithelial cells.

We have examined the effects of depleting lumenal Ca2+ on the synthesis, phosphorylation and secretion of caseins in lactating mouse mammary cells by using inhibitors of the endoplasmic reticulum Ca(2+)-ATPase or the ionophore ionomycin in the absence of external Ca2+. Treatment with these drugs resulted in a transient increase in the cytosolic Ca2+ concentration due to Ca2+ mobilization. Protein synthesis over a 1 h period was substantially inhibited by Ca2+ depletion, but in a pulse-chase protocol secretion of pre-synthesized proteins was unaffected by Ca2+ depletion. Analysis of polysome profiles showed that Ca2+ depletion resulted in a loss of polysomes, consistent with an inhibition of initiation of protein synthesis. Neither treatment with Ca(2+)-ATPase inhibitors to deplete endoplasmic reticulum Ca2+ nor treatment with ionomycin/EGTA had any effect on an early phase of phosphorylation of alpha- or beta/gamma-caseins, but Ca2+ depletion resulted in a decrease in a late phase of casein phosphorylation. These results indicate that lumenal Ca2+ is required to maintain protein synthesis in lactating mammary cells but is not required for protein secretion, and that Ca2+ accumulation in the Golgi cisternae is required for a late but not for an early phase of casein phosphorylation.

Animals↗

PubMed1999

A single nucleotide deletion resulting in a premature stop codon is associated with marked reduction of transcripts from a goat beta-casein null allele.

A null beta-casein allele (CSN2O) was investigated in Creole and Pyrenean goats producing milk devoid of beta-casein (CSN2). Northern blot analyses of total mammary RNA showed much lower amounts of CSN2 transcripts that were similar in size to the wild-type counterpart. The amount of CSN2O mRNA was roughly 5% of the amount of mRNA obtained at the same age and stage of lactation from CSN2A/A goats. Comparative sequence analyses of full-length CSN2O and CSN2A cDNAs showed that both alleles were of similar size, but allele CSN2O had a one-nucleotide deletion in the 5' end of exon 7, which introduces a premature stop codon. The open reading frame of allele CSN2O encodes a shortened polypeptide of 72 amino acids, compared to 223 amino acids for caprine pre beta-casein A. Comparative analyses of RT-PCR products suggested that alleles CSN2O and CSN2A might also differ in the amount and relative ratio of minor deleted CSN2 transcripts. The lower amount of CSN2O mRNA was associated with the occurrence of the premature stop codon which may mediate a rapid decay of CSN2O mRNA and promote skipping of nucleotide stretches containing premature nonsense triplets.

Alleles↗

PubMed1997

Specific peptides of casein pancreatic digestion enhance the production of tetanus toxin.

Casein pancreatic digest is the basic bacterial growth medium used for diphtheria, botulinum and tetanus toxin vaccine production. It is known that the variation in the peptide content of the casein digest directly affects final toxin yields. In this study, the identification and sequences of eight peptides, four to eight amino acids in length, of casein pancreatic digestion, which seem to be involved in the enhancement of tetanus toxin production, are described. They all contain one or two residues of proline/molecule and a predominance of hydrophobic amino acid residues. The most active peptides show a general structure of Pro-aromatic-Pro, and this pattern resembled the motif displayed by bradykinin-potentiating peptides found in snake venoms. By analogy with the mechanism of bradykinin potentiation through inhibition of the proteolytic degradation of bradykinin, it is suggested that the six peptides identified here could protect the tetanus toxin from proteolysis, once secreted by the bacteria.

Animals↗

PubMed1998

Reconstruction of the proteolytic pathway for use of beta-casein by Lactococcus lactis.

Amino acid auxotrophous bacteria such as Lactococcus lactis use proteins as a source of amino acids. For this process, they possess a complex proteolytic system to degrade the protein(s) and to transport the degradation products into the cell. We have been able to dissect the various steps of the pathway by deleting one or more genes encoding key enzymes/components of the system and using mass spectrometry to analyse the complex peptide mixtures. This approach revealed in detail how L. lactis liberates the required amino acids from beta-casein, the major component of the lactococcal diet. Mutants containing the extracellular proteinase PrtP, but lacking the oligopeptide transport system Opp and the autolysin AcmA, were used to determine the proteinase specificity in vivo. To identify the substrates of Opp present in the casein hydrolysate, the PrtP-generated peptide pool was offered to mutants lacking the proteinase, but containing Opp, and the disappearance of peptides from the medium as well as the intracellular accumulation of amino acids and peptides was monitored in peptidase-proficient and fivefold peptidase-deficient genetic backgrounds. The results are unambiguous and firmly establish that (i) the carboxyl-terminal end of beta-casein is degraded preferentially despite the broad specificity of the proteinase; (ii) peptides smaller than five residues are not formed in vivo; (iii) use of oligopeptides of 5-10 residues becomes only possible after uptake via Opp; (iv) only a few (10-14) of the peptides generated by PrtP are actually used, even though the system facilitates the transport of oligopeptides up to at least 10 residues. The technology described here allows us to monitor the fate of individual peptides in complex mixtures and is applicable to other proteolytic systems.

Amino Acid Sequence↗

PubMed1996

Down-regulation of anti-CD3 antibody-induced IL-4 production by bovine caseins hydrolysed with Lactobacillus GG-derived enzymes.

A prerequisite for systemic hyporesponsiveness to dietary antigens is their processing in the gut. This study investigated whether bovine caseins degraded by enzymes of an intestinal bacterial strain, Lactobacillus GG (ATCC 53103), could regulate the cytokine production by anti-CD3 antibody-induced peripheral blood mononuclear cells of 14 atopic patients, aged 5-29 (mean, 16) months. Purified casein up-regulated the interleukin-4 and interferon-gamma production, P = 0.008 and P = 0.008, respectively. Conversely, Lactobacillus GG-degraded casein down-regulated the interleukin-4 production, P = 0.003, with no effect on interferon-gamma. These results indicate that intestinal bacteria may modify immunomodulatory properties of native food proteins and introduce a promising tool to provide protection from potentially harmful dietary antigens at a young age.

Adolescent↗

PubMed2003

Roles of OsCKI1, a rice casein kinase I, in root development and plant hormone sensitivity.

Casein kinases are critical in cell division and differentiation across species. A rice cDNA fragment encoding a putative casein kinase I (CKI) was identified via cDNA macroarray under brassinosteroid (BR) treatment, and a 1939-bp full-length cDNA, OsCKI1, was isolated and found to encode a putative 463-aa protein. RT-PCR and Northern blot analysis indicated that OsCKI1 was constitutively expressed in various rice tissues and upregulated by treatments with BR and abscisic acid (ABA). Enzymatic assay of recombinant OsCKI1 proteins expressed in Escherichia coli showed that the protein was capable of phosphorylating casein. The physiological roles of OsCKI1 were studied through antisense transgenic approaches, and homozygous transgenic plants showed abnormal root development, including fewer lateral and adventitious roots, and shortened primary roots as a result of reduced cell elongation. Treatment of wild-type plants with CKI-7, a specific inhibitor of CKI, also confirmed these functions of OsCKI1. Interestingly, in transgenic and CKI-7-treated plants, exogenously supplied IAA could restore normal root development, and measurement of free IAA content in CKI-deficient primary and adventitious roots revealed altered auxin content, indicating that OsCKI1 is involved in auxin metabolism or that it may affect auxin levels. Transgenic plants were less sensitive than control plants to ABA or BR treatment during germination, suggesting that OsCKI1 may be involved in various hormone-signaling pathways. OsCKI1-GFP fusion studies revealed the localization of OsCKI1 to the nucleus, suggesting a possible involvement in regulation of gene expression. In OsCKI1-deficient plants, differential gene expression was investigated using cDNA chip technology, and results indicated that genes related to signal transduction and hormone metabolism were indeed with altered expression.

Amino Acid Sequence↗