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Structural Properties of Casein Micelles with Adjusted Micellar Calcium Phosphate Content.

ABSTRACT: Micellar calcium phosphate (MCP) content of skim milk was modified by pH adjustment followed by dialysis. Turbidity, casein micelle size and partitioning of Ca and caseins between the colloidal and soluble phases of milk were determined. Protein structure was characterised by Fourier transform infrared (FTIR) spectroscopy and proton nuclear magnetic resonance (¹H NMR), whereas organic and inorganic phosphorus were studied by phosphorus-31 nuclear magnetic resonance (³¹P NMR). The sample with the lowest MCP content (MCP7) exhibited the smallest particle size and turbidity, measuring 83 ± 8 nm and 0.08 ± 0.01 cm^-1, respectively. Concentrations of soluble caseins increased with decreasing MCP levels. At ~60% MCP removal, FTIR analysis indicated a critical stage of structural rearrangement and ³¹P NMR analysis showed an increase in signal intensity for Ca-free Ser-P, which further increased as MCP concentration was further reduced. In conclusion, this study highlighted the importance of MCP in maintaining micellar structure and its impact on the integrity of casein micelle.

SUBMITTER: Ahmadi E

PROVIDER: S-EPMC10815582 | biostudies-literature | 2024 Jan

REPOSITORIES: biostudies-literature

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Structural Properties of Casein Micelles with Adjusted Micellar Calcium Phosphate Content.

Ahmadi Elaheh E Markoska Tatijana T Huppertz Thom T Vasiljevic Todor T

Foods (Basel, Switzerland) 20240119 2

Micellar calcium phosphate (MCP) content of skim milk was modified by pH adjustment followed by dialysis. Turbidity, casein micelle size and partitioning of Ca and caseins between the colloidal and soluble phases of milk were determined. Protein structure was characterised by Fourier transform infrared (FTIR) spectroscopy and proton nuclear magnetic resonance (<sup>1</sup>H NMR), whereas organic and inorganic phosphorus were studied by phosphorus-31 nuclear magnetic resonance (<sup>31</sup>P NMR ...[more]

PMID: 38275688

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Project description:BackgroundStreptococcus mutans is a common cariogenic bacterium in the oral cavity involved in plaque formation. Casein phosphopeptide-amorphous calcium phosphate (CPP-ACP) has been introduced into tooth mousse to encourage remineralization of dental enamel. The aim of this research was to study the effect of tooth mousse containing CPP-ACP (GC Tooth Mousse®) or CPP-ACP with 0.2% fluoride (CPP-ACPF; GC Tooth Mousse Plus®; GCP) on S. mutans planktonic growth and biofilm formation.MethodsS. mutans was cultivated in the presence of different dilutions of the tooth mousse containing CPP-ACP or CPP-ACPF, and the planktonic growth was determined by ATP viability assay and counting colony-forming units (CFUs). The resulting biofilms were examined by crystal violet staining, MTT metabolic assay, confocal laser scanning microscopy (CLSM), and scanning electron microscope (SEM).ResultsThe CPP-ACP tooth mousse (GC) at a dilution of 5-50 mg/ml (0.5-5%) did not inhibit planktonic growth, and even increased the ATP content and the number of viable bacteria after a 24 h incubation. The same was observed for the CPP-ACPF tooth mousse (GCP), except for the higher concentrations (25 and 50 mg/ml) that led to a drop in the bacterial count. Importantly, both compounds significantly decreased S. mutans biofilm formation at dilutions as low as 1.5-3 mg/ml. 12.5 mg/ml GC and 6.25 mg/ml GCP inhibited biofilm formation by 90% after 4 h. After 24 h, the MBIC90 was 6.25 mg/ml for both. CLSM images confirmed the strong inhibitory effect GC and GCP had on biofilm formation when using 5 mg/ml tooth mousse. SEM images of those bacteria that managed to form biofilm in the presence of 5 mg/ml tooth mousse, showed alterations in the bacterial morphology, where the streptococci appear 25-30% shorter on the average than the control bacteria.ConclusionOur data show that the tooth mousse containing CPP-ACP reduces biofilm formation of the cariogenic bacterium S. mutans without killing the bacteria. The use of natural substances which inhibit biofilm development without killing the bacteria, has therapeutic benefits, especially in orthodontic pediatric patients.

Project description:In recent years, the development of nanoreactors, such as micellar nanoreactors (MNRs) for catalytic transformations, has gained significant attention due to their potential in enhancing reaction rates, selectivity, efficiency, and, as importantly, the ability to conduct organic chemistry in aqueous solutions. Among these, the copper(I)-catalyzed azide-alkyne cycloaddition (CuAAC) reaction represents a pivotal transformation and is widely used in the synthesis of bioconjugates, pharmaceuticals, and advanced materials. This study aims toward advancing our understanding of the design and utilization of polymeric amphiphiles containing tris-triazole ligands as an integral element for CuAAC reactions within MNRs. Specifically, our investigation delves into three critical factors that influence the reaction rate within MNRs: hydrophobicity, architectural configuration of the polymeric ligands, and their concentration. Utilizing the high molecular precision of dendritic amphiphiles, we synthesized polymeric ligands with two distinct architectures, namely, PEG-ditris-triazole amphiphile (DTA) and PEG-monotris-triazole amphiphile (MTA), and explored their CuAAC reactivity through coassembly with commercially available Pluronic P123 amphiphiles. The results indicate that the architecture and the concentration of the polymeric ligands play more dominant roles in influencing the reaction rate than the hydrophobicity of the dendritic blocks. Notably, while MNRs assembled from solely DTA showed a dampened reaction rate, spiking P123 micelles with DTA yielded an MNR with significantly faster rates. Moreover, P123 MNRs spiked with the synthesized MTA demonstrated increased CuAAC reaction rates compared to those spiked with the DTA, and they even outperformed the widely used Tris(benzyltriazolylmethyl)amine ligand. These findings provide valuable insights into the design principles of polymer-based ligands for constructing reactive MNRs and other types of nanoreactors for efficient catalytic transformations.

Project description:Milk alpha-, beta- and kappa-casein proteins assemble into casein micelles in breast epithelial cells. The glycomacropeptide (GMP) tails of kappa-casein that extend from the surface of the micelle are key to assembly and aggregation. Aggregation is triggered by stomach pepsin cleavage of GMP from para-kappa-casein (PKC). While one casein micelle model emphasizes the importance of hydrophobic interactions, another focuses on polar residues. We performed an evolutionary analysis of kappa-casein primary sequence and predicted features that potentially impact on protein interactions. We noted more rapid change in the earlier period (166 to 60 Ma). Pepsin and plasmin cleavage sites were avoided in the GMP, which may partly explain its amino acid composition. Short tandem repeats have led to modest expansions of PKC, and to large GMP expansions, suggesting the GMP is less length constrained. Amino acid compositional constraints were assessed across species. Polarity and hydrophobicity properties were insufficient to explain differences between PKC and GMP. Among polar residues, threonine dominates the GMP, compared to serine, probably reflecting its preference for O-glycosylation over phosphorylation. Glutamine, enriched in the bovine PQ-rich region, is not positionally conserved in other species. Among hydrophobic residues, isoleucine is clearly preferred over leucine in the GMP, and patches of hydrophobicity are not markedly positionally conserved. PKC tyrosine and charged residues showed stronger conservation of position, suggesting a role for pi-interactions, seen in other structurally dynamic protein membraneless assemblies. Independent acquisitions of cysteines are consistent with a trend of increasing stabilization of multimers by covalent disulphide bonds, over evolutionary time. In conclusion, kappa-casein compositional and positional constraints appear to be influenced by modification preferences, protease evasion and protein-protein interactions.

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Structural Properties of Casein Micelles with Adjusted Micellar Calcium Phosphate Content.

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Structural Properties of Casein Micelles with Adjusted Micellar Calcium Phosphate Content.

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