Epitope characterization of a supramolecular protein assembly with a collection of monoclonal antibodies: the case of casein micelle

Polymorphism and molecular characteristics of the CSN1S2 gene in river and swamp buffalo

The αS2-casein (αS2-CN) is a member of the casein family associated with milk traits in ruminants, but so far the buffalo CSN1S2 gene has not been well understood. In this work, the polymorphisms of CSN1S2 in river and swamp buffalo were detected using direct sequencing of polymerase chain reaction (PCR) products. As a result, 13 single nucleotide polymorphisms (SNPs) were identified in the coding sequence (CDS) of CSN1S2 in two types of buffalo, of which eight SNPs were non-synonymous. The amino acid changes caused by c.580T>C and c.642C>G may affect the function of buffalo αS2-CN. A total of 11 CSN1S2 CDS haplotypes were defined, and accordingly 11 variants of buffalo αS2-CN were inferred and named. The CSN1S2 CDSs of both types of buffalo were 669 nucleotides, which encoded a precursor of 222 amino acids (AAs), and the first 15 AAs constitute a signal peptide. The composition and physicochemical characteristics of two types of buffalo αS2-CNs were similar but slightly different from those of cattle αS2-CN. The αS2-CN mature peptides of buffalo and the species of Bos genus contained a casein domain, and their secondary structures were highly consistent, indicating that they are functionally similar. The results here provide initial insights into the variation, characteristics and biological function of buffalo CSN1S2.

Effect of multi-frequency power ultrasound (MFPU) treatment on enzyme hydrolysis of casein

Effect of multi-frequency power ultrasound (MFPU) pretreatments on the degree of hydrolysis (DH) and mechanism of casein during alcalase enzymolysis was investigated. Results showed that MFPU pretreatment in tri-frequency 20/40/60 kHz mode significantly (p < 0.05) improved the DH value of casein. Variation of intrinsic fluorescence spectrum indicated the unfolding and degradation of casein occurred after MFPU pretreatment. Fourier transform infrared spectra showed that α-helix and β-sheet content of MFPU pretreated casein decreased, while β-turn and random coil content increased. Surface topography and nanostructures of caseins were found modified after MFPU pretreatments by the analysis of scanning electron microscopy (SEM) and atomic force microscopy (AFM). The SEM analysis also indicated that the enzymolysis residues of casein pretreated by MFPU were smaller than untreated samples. In conclusion, the MFPU can be used as an efficient pretreatment method to promote the enzymolysis of casein.

Magnetic bead and gold nanoparticle probes based immunoassay for β-casein detection in bovine milk samples

In this work, a double-probe based immunoassay was developed for rapid and sensitive determination of β-casein in bovine milk samples. In the method, magnetic beads (MBs), employed as supports for the immobilization of anti-β-casein polyclonal antibody (PAb), were used as the capture probe. Colloidal gold nanoparticles (AuNPs), employed as a bridge for loading anti-β-casein monoclonal antibody (McAb) and horseradish peroxidase (HRP), were used as the amplification probe. The presence of β-casein causes the sandwich structures of MBs-PAb-β-casein-McAb-AuNPs through the interaction between β-casein and the anti-β-casein antibodies. The HRP, used as an enzymatic-amplified tracer, can catalytically oxidize the substrate 3,3',5,5'-tetramethylbenzidine (TMB), generating optical signals that are proportional to the quantity of β-casein. The linear range of the immunoassay was from 6.5 to 1520ngmL(-1). The limit of detection (LOD) was 4.8ngmL(-1) which was 700 times lower than that of MBs-antibody-HRP based immunoassay and 6-7 times lower than that from the microplate-antibody-HRP based assay. The recoveries of β-casein from bovine milk samples were from 95.0% to 104.3% that had a good correlation coefficient (R(2)=0.9956) with those obtained by an official standard Kjeldahl method. For higher sensitivity, simple sample pretreatment and shorter time requirement of the antigen-antibody reaction, the developed immunoassay demonstrated the viability for detection of β-casein in bovine milk samples.

Enzyme-antibody dual labeled gold nanoparticles probe for ultrasensitive detection of κ-casein in bovine milk samples

A dual labeled probe was synthesized by coating gold nanoparticles (AuNPs) with anti-κ-CN monoclonal antibody (McAb) and horseradish peroxidase (HRP) enzyme on their surface. The McAb was used as detector and HRP was used as label for signal amplification catalytically oxidize the substrate. AuNPs were used as bridges between the McAb and HRP. Based on the probe, an immunoassay was developed for ultrasensitive detection of κ-CN in bovine milk samples. The assay has a linear response range within 4.2-560 ng mL(-1). The limit of detection (LOD) was 4.2 ng mL(-1) which was 10 times lower than that of traditional McAb-HRP based ELISA. The recoveries of κ-CN from three brand bovine milk samples were from 95.8% to 111.0% that had a good correlation (R(2)=0.998) with those obtained by official standard Kjeldahl method. For higher sensitivity and as simple as the traditional ELISA, the developed immunoassay could provide an alternative approach for ultrasensitive detection of κ-CN in bovine milk sample.

A rapid immunomagnetic beads-based immunoassay for the detection of β-casein in bovine milk

An immunomagnetic beads-based enzyme-linked immunosorbent assay (IMBs-ELISA) was developed for the detection of β-casein in bovine milk. Immunomagnetic beads (IMBs) were employed as the solid phase. The anti-β-casein monoclonal antibody (McAb) bound to IMBs was used as capture probe and an anti-β-casein polyclonal antibody (PcAb), labelled with horseradish peroxidase (HRP), was employed as detector probe. Three reaction and two washing steps were needed. Each reaction needed 10 min or less, which significantly shortened detection compared with classic sandwich ELISA. β-Casein in bovine milk was detected across a linear range (2-128 μg mL(-1)). Application results were in accordance with the Kjejdahl method, which suggests the IMBs-ELISA is rapid and reliable for the detection of β-casein in bovine milk.

A simple competitive enzyme-linked immunosorbent assay for the specific detection of the multiphosphorylated 1–25 β-casein fragment

A specific and simple competitive enzyme-linked immunosorbent assay (ELISA) was developed to determine bovine β-casein phosphopeptides (β-CPP) in casein phosphopeptides (CPP) or CPP complexes such as casein phosphopeptide amorphous calcium phosphate complexes added into dairy products. The method combines sample pretreatment designed for CPP enrichment and anti-β-CPP(f(1–25)) monoclonal antibody 1A5 (mAb 1A5). The mAb 1A5 bound specifically to the tryptic phosphopeptides from β-casein but not from αs1- or αs2-casein. Reactivity was also influenced by the extent of the phosphorylated form of serine residues. Based on the sequence-specific recognition and contribution of phosphorylated serine residues, the epitope of mAb 1A5 was found to reside within the cluster motif Ser(P)-Ser(P)-Ser(P)-Glu-Glu and the surrounding residues in β-CPP. The competitive ELISA developed here can be used as an alternative to specialised and expensive techniques such as mass spectrometry. In particular, it is suitable for the measurement of CPP or CPP complexes in dairy products, which contain closely related endogenous molecular species.

In vivo digestion of infant formula in piglets: protein digestion kinetics and release of bioactive peptides

The first months of life correspond to a key period in human life where dramatic physiological changes (establishment of microbiota, development of the immune system, etc.) occur. In order to better control these changes it is necessary to understand the behaviour of food in the gastrointestinal tract of the newborn. Infant formula is the only food for the newborn when breast-feeding is impossible. The kinetics of digestion of milk proteins and the nature of the peptides liberated in the small intestine throughout infant formula digestion have never been extensively investigated so far and were therefore studied using the piglet as a model of the newborn child. Piglets were fed infant formula by an automatic delivery system during 28 d, and slaughtered 30, 90 and 210 min after the last meal. Contents of stomach, proximal and median jejunum and ileum were collected and characterised. The extent of β-lactoglobulin (β-lg), α-lactalbumin (α-la) and casein proteolysis was monitored by inhibition ELISA, SDS-PAGE, immunoblotting and MS. At 30 min after the last meal, caseins were shown to be extensively hydrolysed in the stomach. Nevertheless, peptides originating mainly from β-caseins (from 509 to 2510 Da) were identified in the jejunum and ileum of the piglets. β-Lg partially resisted gastric digestion but completely disappeared in the stomach after 210 min. α-La had a similar behaviour to that of β-lg. Two large peptides (4276 and 2674 Da) generated from β-lg were present in the ileum after 30 and 210 min and only one (2674 Da) after 90 min.

Allergenic and immunogenic potential of cow's milk β-lactoglobulin and caseins evidenced without adjuvant in germ-free mice

SCOPE

In most animal models of allergy, the development of an IgE response requires the use of an adjuvant. Germ-free (GF) mice exhibit Th2-polarized antibody responses combined with defective immunosuppressive mechanisms. The sensitizing potential of milk proteins was investigated in GF mice in the absence of adjuvant.

METHODS AND RESULTS

β-lactoglobulin (BLG) and whole casein (CAS) allergenicity was evaluated by means of intraperitoneal injections without adjuvant. Injections of BLG induced significant IgE and IgG1 responses in GF mice, while CAS injections provoked the production of IgG1 toward κ- and αS1-caseins. No significant antibody response was evidenced in conventional (CV) mice. After in vitro BLG-reactivation, IL-4, IL-5, IL-13 and IFN-γ productions by splenocytes were higher in GF mice than in CV mice. Heat-treatment decreased BLG allergenicity as indicated by the absence of IgE production in GF mice. However, heat-treatment increased protein immunogenicity and led to the production of anti-BLG and anti-κ-casein IgG1 in both GF and CV mice. This correlated with enhanced productions of IL-4, IL-5 and IL-13 in BLG-reactivated splenocytes from CV mice.

CONCLUSION

Gut colonization by commensal bacteria appeared then to significantly reduce the susceptibility of mice toward the intrinsic allergenic and immunogenic potential of milk proteins.

Topography of the casein micelle surface by surface plasmon resonance (SPR) using a selection of specific monoclonal antibodies

Several theoretical models of the casein micelle structure have been proposed in the past, but the exact organization of the four individual caseins (α(s1), α(s2), β, and κ) within this supramolecular structure remains unknown. The present study aims at determining the topography of the casein micelle surface by following the interaction between 44 monoclonal antibodies specific for different epitopes of α(s1)-, α(s2)-, β-, and κ-casein and the casein micelle in real time and no labeling using a surface plasmon resonance (SPR)-based biosensor. Although the four individual caseins were found to be accessible for antibody binding, data confirmed that the C-terminal extremity of κ-casein was highly accessible and located at the periphery of the structure. When casein micelles were submitted to proteolysis, the C-terminal extremity of κ-casein was rapidly hydrolyzed. Disintegration of the micellar structure resulted in an increased access for antibodies to hydrophobic areas of α(s1)- and α(s2)-casein.

Molecular and immunological characterization of Fasciola antigens recognized by the MM3 monoclonal antibody

Fascioliasis is a re-emerging parasitosis produced by liver flukes of the genus Fasciola. In this study we used protein fingerprinting (PMF) and MS/MS analysis to investigate the Fasciola secretory antigens that are recognized by mAb MM3. The results showed that mAb MM3 binds to several Fasciola cathepsins L1 and L2, but also co-purifies a Kunitz-type protein previously described in F. hepatica, which appears to bind to Fasciola cathepsins L. After identifying the target antigens for mAb MM3, we cloned and expressed a cathepsin L1 isoform in E. coli (gb|FR848428), which after refolding exhibited the MM3-recognized epitope and displayed cysteine protease activity. Using native, folded-recombinant and denatured-recombinant Fasciola cathepsins L as targets, we demonstrated that during F. hepatica infections in sheep, antibody responses to linear and conformational epitopes present on cathepsins L are promoted. However, the antibody response to linear epitopes was only detected in significant amounts in animals suffering from repeated infections. A different antibody response to linear and conformational epitopes also appears to occur in rabbits immunized with native or recombinant unfolded cathepsins, as sera from animals immunized with the latter did not react with native cathepsins and vice versa. In addition, the ELISA inhibitions showed that the MM3 epitope is not recognized by rabbits, which explains the usefulness of these species for producing capture antibodies for use in MM3-ELISA assays.

Immune activation by casein dietary antigens in bipolar disorder

OBJECTIVES

  Inflammation and other immune processes are increasingly linked to psychiatric diseases. Antigenic triggers specific to bipolar disorder are not yet defined. We tested whether antibodies to bovine milk caseins were associated with bipolar disorder, and whether patients recognized different epitopes of the casein protein than control individuals.

METHODS

  Anti-bovine casein immunoglobulin G (IgG) levels were measured with solid-phase immunoassays in 75 individuals with bipolar disorder and 65 controls. Epitope recognition was evaluated in immunoassays by cross neutralization with anti-bovine casein polyclonal antibodies of defined reactivity. Group-specific reactivity and associations with symptom severity scores were detected with age-, gender-, and race-controlled regression models.

RESULTS

  Individuals with bipolar disorder had significantly elevated anti-casein IgG (t-test, p ≤0.001) compared to controls. Casein IgG seropositivity conferred odds ratios of 3.97 for bipolar disorder [n=75, 95% confidence interval (CI): 1.31-12.08, p ≤0.015], 5.26 for the bipolar I subtype (n=56, 95% CI: 1.66-16.64, p ≤0.005), and 3.98 for bipolar disorder with psychosis (n=54, 95% CI: 1.32-12.00, p ≤0.014). Lithium and/or antipsychotic medication did not significantly affect anti-casein IgG levels. Casein IgG measures correlated with severity of manic (R(2) =0.15, 95% CI: 0.05-0.24, p ≤0.02) but not depressive symptoms. Unlike controls, sera from individuals with bipolar disorder did not inhibit binding of casein-reactive animal sera (t-test/χ(2) , p ≤0.0001).

CONCLUSIONS

  Anti-casein IgG associations with bipolar I diagnoses, psychotic symptom history, and mania severity scores suggest that casein-related immune activation may relate to the psychosis and mania components of this mood disorder. Case-control differences in epitope recognition implicate disease-related alterations in how the casein molecule is digested and/or how resulting casein-derived structures are rendered immunogenic.

Subunit and whole molecule specificity of the anti-bovine casein immune response in recent onset psychosis and schizophrenia

Previous studies show increased antibody levels to bovine casein in some individuals with schizophrenia. The immunogenicity of specific domains of bovine casein varies among people with milk sensitivities and thus could vary among different neuropsychiatric disorders. Using ELISAs and immunoblotting, we characterized IgG class antibody specificity to whole bovine casein and to the alpha(s), beta, and kappa subunits in individuals with recent onset psychosis (n=95), long-term schizophrenia (n=103), and non-psychiatric controls (n=65). In both patient groups, we found elevated IgG to casein proteins, particularly to whole casein and the alpha(s) subunit (p<or=0.0001). Odds ratios of casein seroprevalence for recent onset psychosis (age-, gender-, race-, smoking-adjusted) were significant for whole casein (8.13, p<or=0.0001), and the alpha(s) (7.89, p<or=0.0001), beta (5.23, p<or=0.001) and kappa (5.70, p<or=0.0001) subunits. Odds ratios for long-term schizophrenia were significant for whole casein (7.85, p<or=0.0001), and the alpha(s) (4.78, p<or=0.003) and kappa (4.92, p<or=0.004) subunits. Within the recent onset group, odds ratios were particularly significant for a subgroup of people with psychotic disorders that included major depressive disorders (8.22-16.48, p<or=0.0001). In a different recent onset subgroup (schizophrenia-spectrum disorders), PANSS scores for negative symptoms were correlated with casein antibody levels for the alpha(s) and kappa subunits (p<or=0.001-0.01). Immunoblotting patterns also exhibited group specificity, with kappa predominant in recent onset and alpha(s) in schizophrenia (Fisher's Exact Test, p<or=0.001). The elevated IgG and unique patterns of antibody specificity to bovine casein among diagnostic groups provide a rationale for clinical trials to evaluate efficacies of dietary modifications in individuals with neuropsychiatric diseases.