A quantitative calcium phosphate nanocluster model of the casein micelle: the average size, size distribution and surface properties

Holt, Carl

doi:10.1007/s00249-021-01533-5

Cited by 32 publications

(23 citation statements)

References 148 publications

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“…Among proteins that have been tested for delivery systems, milk protein (e.g., casein) has proven an efficient encapsulation material owing to its structural and functional properties [ 4 , 5 , 6 ]. The milk protein, casein, exhibits an unfolded conformation required to form a thermodynamically stable complex with amorphous calcium phosphate [ 7 ]. In their native state, casein micelles are polydisperse, spherical particles with a mean diameter of 160 nm [ 8 ].…”

Section: Introductionmentioning

confidence: 99%

Effect of Transglutaminase Post-Treatment on the Stability and Swelling Behavior of Casein Micro-Particles

Gebhardt

Khanna

Schulte

et al. 2022

IJMS

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Casein microparticles are produced by flocculation of casein micelles due to volume exclusion of pectin and subsequent stabilization by film drying. Transglutaminase post-treatment alters their stability, swelling behavior, and internal structure. Untreated particles sediment due to their size and disintegrate completely after the addition of sodium dodecyl sulfate. The fact that transglutaminase-treated microparticles only sediment at comparable rates under these conditions shows that their structural integrity is not lost due to the detergent. Transglutaminase-treated particles reach an equilibrium final size after swelling instead of decomposing completely. By choosing long treatment times, swelling can also be completely suppressed as experiments at pH 11 show. In addition, deswelling effects also occur within the swelling curves, which enhance with increasing transglutaminase treatment time and are ascribed to the elastic network of cross-linked caseins. We propose a structural model for transglutaminase-treated microparticles consisting of a core of uncross-linked and a shell of cross-linked caseins. A dynamic model describes all swelling curves by considering both casein fractions in parallel. The characteristic correlation length of the internal structure of swollen casein microparticles is pH-independent and decreases with increasing transglutaminase treatment time, as observed also for the equilibrium swelling value of uncross-linked caseins.

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Section: Introductionmentioning

confidence: 99%

Effect of Transglutaminase Post-Treatment on the Stability and Swelling Behavior of Casein Micro-Particles

Gebhardt

Khanna

Schulte

et al. 2022

IJMS

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“…Schematic illustration of casein micelles as extracellular condensates containing intrinsically disordered caseins, CaP nanoclusters and small ions such as Ca 2+ . An expanded snapshot of the liquid droplet‐like structure near the surface of one of the CaP nanoclusters in the multivalent model of casein micelles [11,14] is also shown. Droplet‐promoting regions involved in transient interactions between the caseins, such as those predicted by the FuzDrop method (Figs 3 and 5), are shown in blue.…”

Section: Discussionmentioning

confidence: 99%

“…Fuzziness is a feature of these complexes as their conformations and interaction properties can adapt to the cellular context and thus can change with cellular conditions [9,39]. The association of the intrinsically disordered caseins, for example, to form casein micelles, can take place via multiple contact sites of different sequence motifs and thus can be described by multivalency [11,14]. Along these lines, the interactions between the caseins within the casein micelle are multivalent and involve SLiMs.…”

Section: Multivalent Interactions Between Intrinsically Disordered Pr...mentioning

confidence: 99%

“…The application to caseins of the concepts developed for intrinsically disordered proteins has led to a detailed and multivalent binding model of casein micelles that accounts accurately for their size, substructure, polydispersity and composition [3,6,[10][11][12][13][14]. According to these studies, about 70% of the casein molecules within casein micelles are bound directly to the CaP nanoclusters through their CaP-SLiMs, whereas the rest are considered to be free of direct linkages.…”

Section: Introduction: Caseins and Casein Micellesmentioning

confidence: 99%

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Are casein micelles extracellular condensates formed by liquid‐liquid phase separation?

et al. 2022

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Casein micelles are extracellular polydisperse assemblies of unstructured casein proteins. Caseins are the major component of milk. Within casein micelles, casein molecules are stabilised by binding to calcium phosphate nanoclusters and, by acting as molecular chaperones, through multivalent interactions. In the light of such interactions, we discuss whether casein micelles can be considered as extracellular condensates formed by liquid-liquid phase separation. We analyse the sequence, structure and interactions of caseins in comparison with proteins forming intracellular condensates. Furthermore, we review the similarities between caseins and small heat-shock proteins whose chaperone activity is linked to phase separation of proteins. By bringing these observations together, we describe a regulatory mechanism for protein condensates, as exemplified by casein micelles.

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“…[5,6] Caseins are organized into approximately spherical colloidal structures called casein micelles (CMs) with sizes distributed between 50 and 100 nm. [7] In cow's milk, they consist of four inherently disordered proteins (𝛼 S1 -, 𝛼 S2 -, 𝛽and 𝜅-caseins) and colloidal calcium phosphate, which is distributed throughout the micelle in the form of calcium phosphate nanoclusters. [8,9] Caseins can be described as block copolymers due to their binding behavior to hydrophobic surfaces and the fact that their primary structure has well-defined hydrophilic and hydrophobic regions.…”

Section: Introductionmentioning

confidence: 99%

Fine Structure and Swelling Properties of Fibers from Regenerated Rennet‐Treated Casein Micelles

Thill

Schmidt

Jana

et al. 2022

Macro Materials & Eng

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Regenerated fibers from rennet‐treated casein micelles can be produced with a defined width and homogeneous surface morphology using a two‐substance nozzle integrated in a spinning setup. Extrusion is carried out under standard conditions in a coagulation buffer with 100 × 10−3 m CaCl2 at 60 °C. Electron microscopic images of dried fibers show a fine structure consisting of µm‐sized strands running parallel to the fiber axis and radially outward. Confocal fluorescence microscopy lifetime images show that the strands are rich in free calcium, which is released upon swelling in deionized water and diffuses out of the fiber. Fibers made with only 50 × 10−3 m calcium chloride swell at a higher rate to larger equilibrium swelling values because of fewer stabilizing calcium bridges. In HCl, initial swelling of the fibers is followed by deswelling to a defined equilibrium state with a densely packed casein matrix, as indicated by fluorescence microscopy images. Because of the large number of dissolved calcium contacts and the residual charges on the casein, swelling in HCl occurs very quickly. Elastic contributions of the network and released ions lead to deswelling of the fiber, which occurs fastest for those with 100 × 10−3 m CaCl2 due to the high proportion of free ions.

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A quantitative calcium phosphate nanocluster model of the casein micelle: the average size, size distribution and surface properties

Cited by 32 publications

References 148 publications

Effect of Transglutaminase Post-Treatment on the Stability and Swelling Behavior of Casein Micro-Particles

Effect of Transglutaminase Post-Treatment on the Stability and Swelling Behavior of Casein Micro-Particles

Are casein micelles extracellular condensates formed by liquid‐liquid phase separation?

Fine Structure and Swelling Properties of Fibers from Regenerated Rennet‐Treated Casein Micelles

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