1
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The self-association properties of partially dephosphorylated bovine beta-casein. Food Hydrocoll 2023. [DOI: 10.1016/j.foodhyd.2022.108019] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
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2
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Sun Y, Tai Z, Yan T, Dai Y, Hemar Y, Li N. Unveiling the structure of the primary caseinate particle using small-angle X-ray scattering and simulation methodologies. Food Res Int 2021; 149:110653. [PMID: 34600655 DOI: 10.1016/j.foodres.2021.110653] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/30/2021] [Revised: 08/11/2021] [Accepted: 08/17/2021] [Indexed: 11/27/2022]
Abstract
The low-resolution structure of casein (CN) clusters in sodium caseinate (NaCas) solution and its conformational dynamics were obtained by size-exclusion chromatography (SEC), analytical ultracentrifugation (AUC), small-angle X-ray scattering (SAXS), and molecular dynamics (MD) simulations. The results of sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) and native PAGE revealed that the casein clusters consisted predominantly of α- and β-CN complexes, and a trace amount of κ-CN. The AUC analysis indicated that the casein clusters were composed of 34.6% of casein monomers, 19.2%, 20.4%, and 25.8% of complexes with molar weight (Mw) of ~50.3, ~70.6, and ~133 kDa, respectively. The volume fractions of components in casein clusters were quantified as 64.3% of αs1-β-αs2-CN, 22.3% of αs1-CN, 8.5% of αs2-CN, and 4.4% of αs1-αs2-CN, respectively. The ensemble optimization method (EOM) gave a fitting result where αs1-β-αs2-CN species coexisted in ~35.3% under compact conformation and ~64.7% in elongated conformation in solution. The three-dimensional structures of αs1-β-αs2-CN from EOM showed a good overlay on the casein clusters ab initio model obtained from DAMMIN and DAMMIX program. MD simulations revealed that αs1-β-αs2-CN underwent a conformational change from the elongated state into the compact state within the initial 200 ns of simulations. The addition of nonionic surfactants affected little the backbone-to-backbone interactions in the formation of the casein clusters. We propose that αs1-CN, β-CN, αs2-CN, and κ-CN associated in consecutive steps into casein clusters, and a trace of κ-CN may be located at the surface of the assemblies limiting the growth of casein aggregates.
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Affiliation(s)
- Yang Sun
- College of Vocational and Technical Education, Yunnan Normal University, Yieryi Avenue, No. 298, 650092 Kunming, Yunnan, People's Republic of China.
| | - Zhonghong Tai
- College of Vocational and Technical Education, Yunnan Normal University, Yieryi Avenue, No. 298, 650092 Kunming, Yunnan, People's Republic of China
| | - Tingting Yan
- College of Vocational and Technical Education, Yunnan Normal University, Yieryi Avenue, No. 298, 650092 Kunming, Yunnan, People's Republic of China
| | - Yiqi Dai
- College of Vocational and Technical Education, Yunnan Normal University, Yieryi Avenue, No. 298, 650092 Kunming, Yunnan, People's Republic of China
| | - Yacine Hemar
- Catalyst Tec Limited., 16 Beatrice Tinsley Cresecnt, Rosedale 0632, Auckland, New Zealand; International Joint Research Laboratory for Functional Dairy Protein Ingredients, U.S.-China, People's Republic of China
| | - Na Li
- National Facility for Protein Science in Shanghai, Zhangjiang Lab, Shanghai Advanced Research Institute, CAS, No.333, Haike Road, Shanghai, Shanghai 201210, People's Republic of China.
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3
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Li M, Auty MA, Crowley SV, Kelly AL, O'Mahony JA, Brodkorb A. Self-association of bovine β-casein as influenced by calcium chloride, buffer type and temperature. Food Hydrocoll 2019. [DOI: 10.1016/j.foodhyd.2018.09.035] [Citation(s) in RCA: 20] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
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4
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Smialowska A, Matia-Merino L, Ingham B, Carr A. Effect of calcium on the aggregation behaviour of caseinates. Colloids Surf A Physicochem Eng Asp 2017. [DOI: 10.1016/j.colsurfa.2017.02.074] [Citation(s) in RCA: 15] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/20/2022]
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5
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Secondary structure and colloidal stability of beta-casein in microheterogeneous water-ethanol solutions. Food Hydrocoll 2017. [DOI: 10.1016/j.foodhyd.2016.09.011] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
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6
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Turovsky T, Portnaya I, Kesselman E, Ionita-Abutbul I, Dan N, Danino D. Effect of temperature and loading on the structure of β-casein/ibuprofen assemblies. J Colloid Interface Sci 2015; 449:514-21. [DOI: 10.1016/j.jcis.2015.02.030] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/08/2014] [Revised: 02/10/2015] [Accepted: 02/10/2015] [Indexed: 01/07/2023]
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7
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Kerkhofs S, Leroux F, Allouche L, Mellaerts R, Jammaer J, Aerts A, Kirschhock CEA, Magusin PCMM, Taulelle F, Bals S, Van Tendeloo G, Martens JA. Single-step alcohol-free synthesis of core–shell nanoparticles of β-casein micelles and silica. RSC Adv 2014. [DOI: 10.1039/c4ra03252g] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
β-Casein is wrapped in a thin shell of SiO2 under biocompatible conditions forming hybrid core–shell nanoparticles.
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Affiliation(s)
- Stef Kerkhofs
- Centre for Surface Chemistry and Catalysis
- KU Leuven
- Heverlee, Belgium
| | - Frederic Leroux
- Electron Microscopy for Materials Science (EMAT)
- UAntwerp, Belgium
| | - Lionel Allouche
- Service de R.M.N
- Institut de Chimie
- Université de Strasbourg
- France
| | - Randy Mellaerts
- Centre for Surface Chemistry and Catalysis
- KU Leuven
- Heverlee, Belgium
| | - Jasper Jammaer
- Centre for Surface Chemistry and Catalysis
- KU Leuven
- Heverlee, Belgium
| | - Alexander Aerts
- Centre for Surface Chemistry and Catalysis
- KU Leuven
- Heverlee, Belgium
| | | | | | - Francis Taulelle
- Centre for Surface Chemistry and Catalysis
- KU Leuven
- Heverlee, Belgium
- Tectospin
- Institut Lavoisier
| | - Sara Bals
- Electron Microscopy for Materials Science (EMAT)
- UAntwerp, Belgium
| | | | - Johan A. Martens
- Centre for Surface Chemistry and Catalysis
- KU Leuven
- Heverlee, Belgium
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8
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Effect of calcium ions on both the co-assembly of αs-casein with soy phosphatidylcholine and the novel functionality of their complex particles. Food Hydrocoll 2014. [DOI: 10.1016/j.foodhyd.2013.03.018] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/13/2023]
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9
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Ossowski S, Jackson A, Obiols-Rabasa M, Holt C, Lenton S, Porcar L, Paulsson M, Nylander T. Aggregation behavior of bovine κ- and β-casein studied with small angle neutron scattering, light scattering, and cryogenic transmission electron microscopy. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2012; 28:13577-13589. [PMID: 22924693 DOI: 10.1021/la302416p] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/01/2023]
Abstract
In the native bovine casein micelle the calcium sensitive caseins (α(S1)-, α(S2)- and β-casein) sequester amorphous calcium phosphate in nanometer-sized clusters, whereas the calcium-insensitive κ-casein limits the growth of the micelle. In this paper, we further investigate the self-association of κ- and β-casein, which are two of the key proteins that control the substructure of the milk casein micelle, using neutron and light scattering techniques and cryogenic transmission electron microscopy. Results demonstrate that κ-casein can, apart from the known self-assembly, form amyloid-like fibrils already at temperatures of 25 °C when subject to agitation. This extended aggregation behavior of κ-casein is inhibited by β-casein, as reported by others. These findings have implications for the structure and stability of casein micelles. The neutron scattering data was used to gain information on the self-assembly structure of κ-casein. β-Casein shows similar self-association behavior as κ-casein, but unlike κ-casein, the self-association exhibits temperature dependence within the studied temperatures (6 and 25 °C). Here, we will discuss our extended study of the known self-assembly of casein in the context of the fibrillation of κ-casein.
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Affiliation(s)
- Sofie Ossowski
- Division of Physical Chemistry, Lund University, P.O. Box 124, SE-221 00 Lund, Sweden.
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10
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Bachar M, Mandelbaum A, Portnaya I, Perlstein H, Even-Chen S, Barenholz Y, Danino D. Development and characterization of a novel drug nanocarrier for oral delivery, based on self-assembled β-casein micelles. J Control Release 2012; 160:164-71. [DOI: 10.1016/j.jconrel.2012.01.004] [Citation(s) in RCA: 98] [Impact Index Per Article: 8.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/16/2011] [Revised: 01/05/2012] [Accepted: 01/06/2012] [Indexed: 12/14/2022]
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11
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Le Parc A, Leonil J, Chanat E. AlphaS1-casein, which is essential for efficient ER-to-Golgi casein transport, is also present in a tightly membrane-associated form. BMC Cell Biol 2010; 11:65. [PMID: 20704729 PMCID: PMC2928771 DOI: 10.1186/1471-2121-11-65] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/06/2010] [Accepted: 08/12/2010] [Indexed: 11/10/2022] Open
Abstract
BACKGROUND Caseins, the main milk proteins, aggregate in the secretory pathway of mammary epithelial cells into large supramolecular structures, casein micelles. The role of individual caseins in this process and the mesostructure of the casein micelle are poorly known. RESULTS In this study, we investigate primary steps of casein micelle formation in rough endoplasmic reticulum-derived vesicles prepared from rat or goat mammary tissues. The majority of both alphaS1- and beta-casein which are cysteine-containing casein was dimeric in the endoplasmic reticulum. Saponin permeabilisation of microsomal membranes in physico-chemical conditions believed to conserve casein interactions demonstrated that rat immature beta-casein is weakly aggregated in the endoplasmic reticulum. In striking contrast, a large proportion of immature alphaS1-casein was recovered in permeabilised microsomes when incubated in conservative conditions. Furthermore, a substantial amount of alphaS1-casein remained associated with microsomal or post-ER membranes after saponin permeabilisation in non-conservative conditions or carbonate extraction at pH11, all in the presence of DTT. Finally, we show that protein dimerisation via disulfide bond is involved in the interaction of alphaS1-casein with membranes. CONCLUSIONS These experiments reveal for the first time the existence of a membrane-associated form of alphaS1-casein in the endoplasmic reticulum and in more distal compartments of the secretory pathway of mammary epithelial cells. Our data suggest that alphaS1-casein, which is required for efficient export of the other caseins from the endoplasmic reticulum, plays a key role in early steps of casein micelle biogenesis and casein transport in the secretory pathway.
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Affiliation(s)
- Annabelle Le Parc
- INRA, UR1196 Génomique et Physiologie de la Lactation, Domaine de Vilvert, F-78352 Jouy-en-Josas cedex, France
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12
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Moitzi C, Portnaya I, Glatter O, Ramon O, Danino D. Effect of temperature on self-assembly of bovine beta-casein above and below isoelectric pH. Structural analysis by cryogenic-transmission electron microscopy and small-angle X-ray scattering. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2008; 24:3020-3029. [PMID: 18327957 DOI: 10.1021/la702802a] [Citation(s) in RCA: 48] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/26/2023]
Abstract
beta-Casein is one of the main proteins in milk, recently classified as an intrinsically unstructured protein. At neutral pH, it is composed of a highly polar N-terminus domain and a hydrophobic C-terminus tail. This amphiphilic block-copolymer-like structure leads to self-organization of the protein monomers into defined micelles. Recently, it has been shown that at room temperature, beta-casein also self-organizes into micelles in an acidic environment, but the effect of temperature on the micelles' formation and properties at the low pH regime were not explored. In the present study, we used two complementary techniques, cryogenic-transmission electron microscopy (cryo-TEM) and small-angle X-ray scattering (SAXS), to characterize at high-resolution the micelles' shape, dimensions, and aggregation numbers and to determine how these properties are affected by temperature between 1 and 40 degrees C. Two different regimes were studied: highly acidic pH where the protein is cationic, and neutral pH, where it is anionic. We found that flat disk-like micelles with low aggregation numbers formed at low temperature in the two pH regimes. Close to neutral pH increase in temperature involves a transition in the micelles' shape and dimensions from flat disks to bulky, almost spheroidal micelles, coupled with a sharp increase in the micelles' aggregation number. In contrast, no effects on the micelles' morphology or aggregation number were detected in the acidic environment within the entire temperature range studied. The self-organization into disk micelles and the lack of effect of temperature in the acidic environment are linked to the unstructured character of the protein and to the charge distribution map. The latter indicates that below the isoelectric pH (pI), beta-casein loses the distinct separation of hydrophobic and hydrophilic domains, thereby suggesting that it may no longer be considered as a classical head-tail block-copolymer amphiphile as in neutral pH.
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Affiliation(s)
- Christian Moitzi
- Institute of Chemistry and Physical Chemistry, University of Graz, Graz A-8010, Austria
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13
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Portnaya I, Ben-Shoshan E, Cogan U, Khalfin R, Fass D, Ramon O, Danino D. Self-assembly of bovine beta-casein below the isoelectric pH. JOURNAL OF AGRICULTURAL AND FOOD CHEMISTRY 2008; 56:2192-8. [PMID: 18303844 DOI: 10.1021/jf072630r] [Citation(s) in RCA: 54] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/13/2023]
Abstract
Beta-casein is an intrinsically unstructured amphiphilic protein that self-assembles into micelles at neutral pH. This paper reports that beta-casein self-organizes into micelles also under acidic conditions. The protein association behavior and micelle characteristics at pH 2.6, well below the p I, are presented. The pH was found to strongly affect the micelle shape and dimensions. Cryogenic transmission electron microscopy (cryo-TEM) experiments revealed disk-like micelles of 20-25 nm in length and approximately 3.5 nm in height in acidic conditions. An aggregation number of 6 was determined by sedimentation equilibrium under these conditions. Isothermal titration calorimetry experiments verified the association below the p I and allowed determination of the micellization enthalpy, the critical micellar concentration, and the micellization relative cooperativity (MR). Small-angle X-ray scattering results at concentrations below the critical micellization concentration (CMC) suggest that the monomeric protein is likely in a premolten globule state at low pH. Calculations of the protein charge at acidic and neutral pH reveal a similar high net charge but considerable differences in the charge distribution along the protein backbone. Overall the results show that beta-casein is amphiphilic at low pH, but the distribution of charge along the protein chain creates packing constraints that affect the micelle organization, leading at concentrations above the CMC to the formation of disk micelles.
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Affiliation(s)
- Irina Portnaya
- Department of Biotechnology, Technion - Israel Institute of Technology, 32000, Israel
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14
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Modifications of the charges at the N-terminus of bovine β-casein: Consequences on its structure and its micellisation. Food Hydrocoll 2007. [DOI: 10.1016/j.foodhyd.2006.03.007] [Citation(s) in RCA: 35] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
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15
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Abstract
The addition of Congo red (CR) dye to diluted raw skim milk resulted in a red shift indicative of the presence of fibril-like structures. Thioflavin T (ThT) is another dye that very specifically binds to protein fibrils, and when added to undiluted raw skim milk, the classic 485 nm fluorescence peak of a ThT-fibril complex was observed. Repeating these experiments with various raw milk components showed that the CR red shift and ThT fluorescence peak were due to the presence of casein micelles, and to a lesser extent, sodium caseinate. Fluorescent peaks were also observed when ThT was added to solutions of purified alpha(S)- and kappa-casein, but not beta-casein, in 0.5 M HEPES buffer (pH = 6.8). The addition of 25 mM Ca(2+) had no effect on beta-casein fluorescence, and significantly reduced the kappacasein peak. However, adding 25 mM Ca(2+) to alpha(S)-casein produced a turbid solution and a 6-fold increase in fluorescence, indicating that the aggregates formed contain fibril-like structure. Casein micelle images obtained by transmission electron microscopy showed the presence of short (7 to 10 nm) fibers cross-linked by dense aggregate junction zones. The observed fibers closely resemble protofibrils, intermediate structures that are observed during the formation of amyloid fibrils.
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Affiliation(s)
- R W Lencki
- Department of Food Science, University of Guelph, Guelph, Ontario, Canada N1G 2W1.
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16
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Burova TV, Grinberg NV, Grinberg VY, Usov AI, Tolstoguzov VB, Kruif CGD. Conformational Changes in ι- and κ-Carrageenans Induced by Complex Formation with Bovine β-Casein. Biomacromolecules 2006; 8:368-75. [PMID: 17291059 DOI: 10.1021/bm060761f] [Citation(s) in RCA: 40] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
The formation of electrostatic complexes between beta-casein and iota- and kappa-carrageenans is well-known. However, the molecular mechanism of the complexation has yet to be determined, particularly with respect to the conformational changes of the interacting macromolecules. High-sensitivity differential scanning calorimetry was used to study beta-casein/carrageenan mixtures at different pH values (3.0 to 7.5), ionic strengths (0.03 and 0.15 M), and various molar protein/polysaccharide ratios (3-400). The effects of these variables on the temperature, enthalpy, and width of the helix-coil transition of iota- and kappa-carrageenans were investigated. Neither pH nor the protein/polysaccharide ratio influenced the transition temperature of either carrageenan in the complexes. However, the transition enthalpy of both carrageenans in complexes with beta-casein decreased to zero with both decreasing pH and increasing protein/polysaccharide ratio. This may reflect an unwinding of the polysaccharide double helix induced by beta-casein, a conformational change which is fully reversible in conditions of sufficiently high ionic strength. The interaction of beta-casein with iota- and kappa-carrageenans was approximated in terms of the model of binding of large ligands to macromolecules, that provides the binding constants for these biopolymers.
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Affiliation(s)
- Tatiana V Burova
- N.M. Emanuel Institute of Biochemical Physics, Russian Academy of Sciences, Vavilov St. 28, 119991, Moscow, Russia.
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Portnaya I, Cogan U, Livney YD, Ramon O, Shimoni K, Rosenberg M, Danino D. Micellization of bovine beta-casein studied by isothermal titration microcalorimetry and cryogenic transmission electron microscopy. JOURNAL OF AGRICULTURAL AND FOOD CHEMISTRY 2006; 54:5555-61. [PMID: 16848545 DOI: 10.1021/jf060119c] [Citation(s) in RCA: 78] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/10/2023]
Abstract
The association behavior, critical micellization concentration (CMC), and enthalpy of demicellization (DeltaHdemic) of bovine beta-casein were studied, for the first time by isothermal titration calorimetry, in a pH 7.0 phosphate buffer with 0.1 ionic strength and in pure water. In the buffer solutions, the CMC decreased asymptotically from 0.15 to 0.006 mM as the temperature was raised from 16 to 45 degrees C. DeltaHdemic decreased with increasing temperature between 16 and 28 degrees C but increased from 28 to 45 degrees C. Thermodynamic analysis below 30 degrees C is consistent with the Kegeles shell model, which suggests a stepwise association process. At higher temperatures, this model exhibits limitations, and the micellization becomes much more cooperative. The CMC values in water, measured between 17 and 28 degrees C, decreased with increasing temperature and, expectedly, were higher than those found in the buffer solutions. beta-Casein micelles were visualized and characterized, for the first time in their hydrated state, using advanced digital-imaging cryogenic transmission electron microscopy. The images revealed small, oblate micelles, about approximately 13 nm in diameter. The micelles shape and dimensions remained nearly constant in the temperature range of 24-35 degrees C.
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Affiliation(s)
- Irina Portnaya
- Department of Biotechnology and Food Engineering and Russell Berrie Nanotechnology Institute, Technion-Israel Institute of Technology, Haifa, 32000 Israel
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18
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Panouillé M, Durand D, Nicolai T. Jamming and Gelation of Dense β-Casein Micelle Suspensions. Biomacromolecules 2005; 6:3107-11. [PMID: 16283734 DOI: 10.1021/bm050438x] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
The rheology of dense suspensions of beta-casein micelles is investigated at pH 6. For a given temperature, the viscosity increases dramatically at a critical concentration (Cc) of about 100 g/L due to jamming of the micelles. For a given concentration close to and above Cc, the viscosity of dense suspensions decreases strongly with increasing temperature because Cc increases. The suspensions show weak shear thickening followed by strong shear thinning. At lower pH, that is, closer to the isoelectric point, spontaneous gelation is observed, which is favored by lowering the temperature and addition of sodium polyphosphate. The gelation process is studied at pH 5.5 by rheology and light scattering.
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Affiliation(s)
- Maud Panouillé
- Polymères, Colloïdes, Interfaces, Unite mixté de recherche, Centre National de la Recherche Scientifique, Université du Maine, 72085 le Mans Cedex 9, France
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19
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Computer simulation of proteins: adsorption, gelation and self-association. Curr Opin Colloid Interface Sci 2004. [DOI: 10.1016/j.cocis.2004.09.005] [Citation(s) in RCA: 45] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
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20
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Livney YD, Schwan AL, Dalgleish DG. A Study of β-Casein Tertiary Structure by Intramolecular Crosslinking and Mass Spectrometry. J Dairy Sci 2004; 87:3638-47. [PMID: 15483147 DOI: 10.3168/jds.s0022-0302(04)73502-x] [Citation(s) in RCA: 52] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
The objective of this study was to obtain experimental evidence to extend the discussion on the 3-D structure of beta-casein (beta-CN). The approach involved the preparation of homobifunctional crosslinkers, bis(sulfosuccinimidyl) derivatives of dicarboxylic acids of several lengths, which specifically react with primary amines of lysinyl residues or the N-terminal in the protein. The intramolecular crosslinks formed were determined by enzymatic digestion and by matrix-assisted laser desorption and ionization time-of-flight mass spectrometry combined with comparison against the theoretical digestion patterns. This procedure allowed the measurement of distances between the crosslinked residues. Ten different masses arising from 8 different specific intramolecular crosslinks were identified. Of these, 5 crosslinks were in good agreement with a published model (Kumosinski et al., 1993). Two other crosslinks each connected 2 residues that are much closer together, according to the model, than the maximum length of the crosslink. However, one of the crosslinks apparently connected 2 residues that are predicted by the model to be 16.7 A farther apart than the crosslink's stretched length. This disparity might be explained by structural flexibility. The structure expressed by the model is probably one of several energetically favorable conformations of the beta-CN molecule, whose structure is best described as rheomorphic rather than either a fixed structure or a random coil.
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Affiliation(s)
- Y D Livney
- Department of Food Science, University of Guelph, ON, Canada N1G 2W1
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21
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O'Connell J, de Kruif C. β-Casein micelles; cross-linking with transglutaminase. Colloids Surf A Physicochem Eng Asp 2003. [DOI: 10.1016/s0927-7757(02)00503-4] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
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22
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Abstract
The association behavior of beta-casein, a protein with a distinct amphipathic character, was studied. beta-Casein exhibits markedly temperature-dependent association behavior; at low temperatures (<10-15 degrees C), monomers predominate, but as the temperature is increased, monomers associate, via hydrophobic bonding, into micelles. beta-Casein micelles have a hydrodynamic radius of approximately 12 nm, a radius of gyration of approximately 8.3 nm, and an interaction radius of approximately 15 nm. These data are fully consistent with a previous fluffy particle. The association behavior of beta-casein is also strongly affected by concentration and solvent quality. At low concentrations beta-casein exhibits a critical micelle concentration (CMC) of approximately 0.05%, w/v, at 40 degrees C. In the presence of 6 M urea the temperature dependence of beta-casein's association behavior is eliminated, leaving monomers predominantly. Temperature-dependent transformations in micelle morphology can be explained by changes in solvent quality, i.e., the temperature-protein hydrophobicity and temperature-voluminosity profiles of beta-casein. The results obtained are consistent with the shell model as developed by Kegeles, in which a distribution of micelle sizes is formed. They contrast with the traditional description of the micellization of beta-casein by a two-state model or by the closed-association model, i.e., monomers if micelles.
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24
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25
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Girardet JM, Debomy L, Courthaudon JL, Miclo TL, Humbert G, Gaillard JL. Viscoelastic properties of oil-water interfaces covered by bovine beta-casein tryptic peptides. J Dairy Sci 2000; 83:2410-21. [PMID: 11104257 DOI: 10.3168/jds.s0022-0302(00)75130-7] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
A combination of proteolysis and dilational rheology has been used to study the behavior of films of beta-casein (beta-CN) and of peptides spread at the oil-water interface. Identification of the peptides produced by trypsin hydrolysis of beta-CN in emulsion at 37 degrees C provided information on the structure of beta-CN adsorbed at the oil-water interface. Good interface properties were observed for beta-CN or its peptides, probably because of the amphipathic nature of beta-CN or a synergistic effect between hydrophilic and hydrophobic peptides. Remarkable surface activity was found for the amphipathic peptide beta-CN (f114-169). Rheological studies had shown that interface films made with peptide fractions or with beta-CN were elastic rather than viscous. Film made with the purified peptide beta-CN (f114-169) was merely elastic at the triolein-water interface. A decrease of the viscoelastic modulus was observed for aging beta-CN film but not for aging peptide films; The beta-CN decrease was related to the flexibility of its structure. When the interface is increased by the dilation of an aqueous droplet plunged into oil, beta-CN may expose new polypeptide trains to cover the increased interface, unlike peptides with simpler structures.
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Affiliation(s)
- J M Girardet
- Laboratoire des BioSciences de l'Aliment, Unité associée à I'INRA, Université Henri Poincaré-Nancy 1, Vandoeuvre-lès-Nancy, France.
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Affiliation(s)
- C Holt
- Hannah Research Institute, Ayr, Scotland
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