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Warncke M, Kieferle I, Nguyen TM, Kulozik U. Impact of heat treatment, casein/whey protein ratio and protein concentration on rheological properties of milk protein concentrates used for cheese production. J FOOD ENG 2022. [DOI: 10.1016/j.jfoodeng.2021.110745] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
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2
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Anema SG. Heat-induced changes in caseins and casein micelles, including interactions with denatured whey proteins. Int Dairy J 2021. [DOI: 10.1016/j.idairyj.2021.105136] [Citation(s) in RCA: 12] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
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3
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Smith GN. An alternative analysis of contrast-variation neutron scattering data of casein micelles in semi-deuterated milk. THE EUROPEAN PHYSICAL JOURNAL. E, SOFT MATTER 2021; 44:5. [PMID: 33590354 DOI: 10.1140/epje/s10189-021-00023-y] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/19/2020] [Accepted: 01/20/2021] [Indexed: 06/12/2023]
Abstract
Contrast-variation small-angle neutron scattering (CV-SANS) is an excellent way to determine the structure of complex, hierarchical colloids, including self-assembled biological systems. In these experiments, the scattering length density of solvents is changed (by varying the ratio of water or [Formula: see text] and heavy water or [Formula: see text]) to highlight or mask scattering from different components in the system. This approach has been used with synthetic colloids, but it is also increasingly being used in the biological and food sciences. Perhaps the most studied food colloid is the "casein micelle," a self-assembled nanometer-scale colloid of the structure-forming casein protein in milk. CV-SANS data available in the literature are typically analyzed using approximations, which may be invalid for casein micelles, as they have been shown to be sticky spheres. To assess the applicability of this approximate approach, a comprehensive set of CV-SANS data from casein micelles in diluted milk was reanalyzed using a model-based approach, where the casein micelles were formally treated as interacting spheres. In general, the conclusions of the previous study are reproduced, but this new approach makes it more straightforward to distinguish the different components in milk and can be applied to any dairy sample with known form of interparticle interactions, which offers the possibility of studying semi-deuterated milk at its native concentration.
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Affiliation(s)
- Gregory N Smith
- Niels Bohr Institute, University of Copenhagen, Universitetsparken 5, 2100, Copenhagen Ø, Denmark.
- ISIS Neutron and Muon Source, Science and Technology Facilities Council, Rutherford Appleton Laboratory, Didcot, OX11 0QX, UK.
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4
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Ma W, Tribet C, Guyot S, Zanchi D. Tannin-controlled micelles and fibrils of κ-casein. J Chem Phys 2020; 151:245103. [PMID: 31893889 DOI: 10.1063/1.5128057] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022] Open
Abstract
Effects of green tea tannin epigallocatechin-gallate (EGCG) on thermal-stress-induced amyloid fibril formation of reduced carboxymethylated bovine milk protein κ-casein were studied by dynamical light scattering and small angle X-ray scattering (SAXS). Two populations of aggregates, micelles, and fibrils dominated the time evolution of light scattering intensity and of effective hydrodynamic diameter. SAXS experiments allowed us to resolve micelles and fibrils so that the time dependence of the scattering profile revealed the structural evolution of the two populations. The low-Q scattering intensity prior to an expected increase in time due to fibril growth shows an intriguing rapid decrease, which is interpreted as the release of monomers from micelles. This phenomenon, observed both in the absence and in the presence of EGCG, indicates that under thermal stress free conditions, native monomers are converted to amyloid-prone monomers that do not form micelles. The consumption of free native monomers results in a release of native monomers from micelles because only native proteins participate in micelle-monomer (quasi)equilibrium. This release is reversible, indicating also that native-to-amyloid-prone monomer conversion is reversible as well. We show that EGCG does not bind to protein in fibrils, neither does it affect/prevent the proamyloid conversion of monomers. EGCG hinders the addition of monomers to growing fibrils. These facts allowed us to propose the kinetics model for EGCG-controlled amyloid aggregation of micellar proteins. Therein, we introduced the growth-rate inhibition function, which quantitatively accounts for the effect of EGCG on the fibril growth at any degree of thermal stress.
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Affiliation(s)
- Wei Ma
- PASTEUR, Département de Chimie, École Normale Supérieure, PSL University, Sorbonne Université, CNRS, 24 rue Lhomond, F-75005 Paris, France
| | - Christophe Tribet
- PASTEUR, Département de Chimie, École Normale Supérieure, PSL University, Sorbonne Université, CNRS, 24 rue Lhomond, F-75005 Paris, France
| | - Sylvain Guyot
- INRA UR1268 BIA-Polyphenols, Reactivity, Processes, F-35653 Le Rheu, France
| | - Dražen Zanchi
- PASTEUR, Département de Chimie, École Normale Supérieure, PSL University, Sorbonne Université, CNRS, 24 rue Lhomond, F-75005 Paris, France
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5
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Ingham B, Smialowska A, Erlangga GD, Matia-Merino L, Kirby NM, Wang C, Haverkamp RG, Carr AJ. Revisiting the interpretation of casein micelle SAXS data. SOFT MATTER 2016; 12:6937-53. [PMID: 27491477 DOI: 10.1039/c6sm01091a] [Citation(s) in RCA: 59] [Impact Index Per Article: 7.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/02/2023]
Abstract
An in-depth, critical review of model-dependent fitting of small-angle X-ray scattering (SAXS) data of bovine skim milk has led us to develop a new mathematical model for interpreting these data. Calcium-edge resonant soft X-ray scattering data provides unequivocal evidence as to the shape and location of the scattering due to colloidal calcium phosphate, which is manifested as a correlation peak centred at q = 0.035 Å(-1). In SAXS data this feature is seldom seen, although most literature studies attribute another feature centred at q = 0.08-0.1 Å(-1) to CCP. This work shows that the major SAXS features are due to protein arrangements: the casein micelle itself; internal regions approximately 20 nm in size, separated by water channels; and protein structures which are inhomogeneous on a 1-3 nm length scale. The assignment of these features is consistent with their behaviour under various conditions, including hydration time after reconstitution, addition of EDTA (a Ca-chelating agent), addition of urea, and reduction of pH.
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Affiliation(s)
- B Ingham
- Callaghan Innovation, P.O. Box 31310, Lower Hutt 5040, New Zealand.
| | - A Smialowska
- School of Food and Nutrition, Massey University, Private Bag 11222, Palmerston North 4442, New Zealand
| | - G D Erlangga
- School of Food and Nutrition, Massey University, Private Bag 11222, Palmerston North 4442, New Zealand
| | - L Matia-Merino
- School of Food and Nutrition, Massey University, Private Bag 11222, Palmerston North 4442, New Zealand
| | - N M Kirby
- Australian Synchrotron, 800 Blackburn Road, Clayton, VIC 3168, Australia
| | - C Wang
- Advanced Light Source, Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA
| | - R G Haverkamp
- School of Engineering and Advanced Technology, Massey University, Private Bag 11222, Palmerston North 4442, New Zealand
| | - A J Carr
- School of Food and Nutrition, Massey University, Private Bag 11222, Palmerston North 4442, New Zealand
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6
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Portnaya I, Avni S, Kesselman E, Boyarski Y, Sukenik S, Harries D, Dan N, Cogan U, Danino D. Competing processes of micellization and fibrillization in native and reduced casein proteins. Phys Chem Chem Phys 2016; 18:22516-25. [DOI: 10.1039/c6cp04582k] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023]
Abstract
Competition between micellization and fibrillization in milk caseins, intrinsically disordered proteins (IDPs).
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Affiliation(s)
- Irina Portnaya
- Department of Biotechnology and Food Engineering
- Technion – Israel Institute of Technology
- Haifa 3200003
- Israel
| | - Sharon Avni
- Department of Biotechnology and Food Engineering
- Technion – Israel Institute of Technology
- Haifa 3200003
- Israel
| | - Ellina Kesselman
- Department of Biotechnology and Food Engineering
- Technion – Israel Institute of Technology
- Haifa 3200003
- Israel
| | - Yoav Boyarski
- Institute of Chemistry and the Fritz Haber Research Center
- The Hebrew University
- Jerusalem 91904
- Israel
| | - Shahar Sukenik
- Institute of Chemistry and the Fritz Haber Research Center
- The Hebrew University
- Jerusalem 91904
- Israel
| | - Daniel Harries
- Institute of Chemistry and the Fritz Haber Research Center
- The Hebrew University
- Jerusalem 91904
- Israel
| | - Nily Dan
- Department of Chemical and Biological Engineering
- Drexel University
- Philadelphia
- USA
| | - Uri Cogan
- Department of Biotechnology and Food Engineering
- Technion – Israel Institute of Technology
- Haifa 3200003
- Israel
| | - Dganit Danino
- Department of Biotechnology and Food Engineering
- Technion – Israel Institute of Technology
- Haifa 3200003
- Israel
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7
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de Kruif C(K, Bhatt H, Anema SG, Coker C. Rheology of caseinate fractions in relation to their water holding capacity. Food Hydrocoll 2015. [DOI: 10.1016/j.foodhyd.2015.05.026] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
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8
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Anema SG, de Kruif C(K. Complex coacervates of lactotransferrin and β-lactoglobulin. J Colloid Interface Sci 2014; 430:214-20. [DOI: 10.1016/j.jcis.2014.05.036] [Citation(s) in RCA: 43] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/02/2014] [Revised: 05/19/2014] [Accepted: 05/21/2014] [Indexed: 02/01/2023]
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9
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Sørensen H, Pedersen JS, Mortensen K, Ipsen R. Characterisation of fractionated skim milk with small-angle X-ray scattering. Int Dairy J 2013. [DOI: 10.1016/j.idairyj.2013.05.006] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/26/2022]
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10
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Comparison of the chaperon activity of glycerol and α-casein on amyloid formation of κ-casein in the presence of glycine and arginine. Biologia (Bratisl) 2013. [DOI: 10.2478/s11756-013-0238-7] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
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11
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de Kruif CGK, Pedersen J, Huppertz T, Anema SG. Coacervates of lactotransferrin and β- or κ-casein: structure determined using SAXS. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2013; 29:10483-10490. [PMID: 23859400 DOI: 10.1021/la402236f] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/02/2023]
Abstract
Lactotransferrin (LF) is a large globular protein in milk with immune-regulatory and bactericidal properties. At pH 6.5, LF (M = 78 kDa) carries a net (calculated) charge of +21. β-Casein (BCN) and κ-casein (KCN) are part of the casein micelle complex in milk. Both BCN and KCN are amphiphillic proteins with a molar mass of 24 and 19 kDa and carry net charges of -14 and -4, respectively. Both BCN and KCN form soap-like micelles, with 40 and 65 monomers, respectively. The net negative charges are located in the corona of the micelles. On mixing LF with the caseins, coacervates are formed. We analyzed the structure of these coarcervates using SAXS. It was found that LF binds to the corona of the micellar structures, at the charge neutrality point. BCN/LF and KCN/LF ratios at the charge neutrality point were found to be ~1.2 and ~5, respectively. We think that the findings are relevant for the protection mechanism of globular proteins in bodily fluids where unstructured proteins are abundant (saliva). The complexes will prevent docking of enzymes on specific charged groups on the globular protein.
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Affiliation(s)
- C G Kees de Kruif
- Van 't Hoff laboratory for Physical and Colloid Chemistry, Padualaan 8, Utrecht University, The Netherlands.
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12
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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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13
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Ghahghaei A, Divsalar A, Faridi N. The effects of molecular crowding on the amyloid fibril formation of alpha-lactalbumin and the chaperone action of alpha-casein. Protein J 2010; 29:257-64. [PMID: 20496103 DOI: 10.1007/s10930-010-9247-3] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Amyloid fibrils arise from the slow aggregation of intermediately folded protein states. In this study the kinetics of the protein fibril formation of alpha-lactalbumin and its prevention by alphaS-casein in the presence and absence of the crowding agent, dextran (68 kDa), have been compared using a thioflavin T binding assay. It was found that alphaS-casein, a molecular chaperone found in bovine milk, is a potent in vitro inhibitor of alpha-lactalbumin fibrillization. The effect of alphaS-casein in preventing fibril formation was significant, although less than it is in the absence of the crowding agent, dextran. The interaction between the chaperone and the alpha-lactalbumin and structural change in the target protein are also shown using intrinsic fluorescence intensity, an ANS binding assay, CD spectroscopy and size-exclusion HPLC. In summary, alpha-casein interacts with alpha-lactalbumin and prevents amyloid formation but not as well as it does when the crowding agent, dextran, not present.
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Affiliation(s)
- Arezou Ghahghaei
- Department of Biology, University of Sistan and Baluchestan, Zahedan, Iran.
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14
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Hidalgo ME, Pires MS, Risso PH. A study on bovine kappa-casein aggregation after the enzymatic action of chymosin. Colloids Surf B Biointerfaces 2010; 76:556-63. [DOI: 10.1016/j.colsurfb.2009.12.018] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/01/2009] [Revised: 12/07/2009] [Accepted: 12/20/2009] [Indexed: 11/16/2022]
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15
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Risso PH, Borraccetti DM, Araujo C, Hidalgo ME, Gatti CA. Effect of temperature and pH on the aggregation and the surface hydrophobicity of bovine κ-casein. Colloid Polym Sci 2008. [DOI: 10.1007/s00396-008-1906-y] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/21/2022]
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16
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Ecroyd H, Koudelka T, Thorn DC, Williams DM, Devlin G, Hoffmann P, Carver JA. Dissociation from the oligomeric state is the rate-limiting step in fibril formation by kappa-casein. J Biol Chem 2008; 283:9012-22. [PMID: 18245081 DOI: 10.1074/jbc.m709928200] [Citation(s) in RCA: 66] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Amyloid fibrils are aggregated and precipitated forms of protein in which the protein exists in highly ordered, long, unbranching threadlike formations that are stable and resistant to degradation by proteases. Fibril formation is an ordered process that typically involves the unfolding of a protein to partially folded states that subsequently interact and aggregate through a nucleation-dependent mechanism. Here we report on studies investigating the molecular basis of the inherent propensity of the milk protein, kappa-casein, to form amyloid fibrils. Using reduced and carboxymethylated kappa-casein (RCMkappa-CN), we show that fibril formation is accompanied by a characteristic increase in thioflavin T fluorescence intensity, solution turbidity, and beta-sheet content of the protein. However, the lag phase of RCMkappa-CN fibril formation is independent of protein concentration, and the rate of fibril formation does not increase upon the addition of seeds (preformed fibrils). Therefore, its mechanism of fibril formation differs from the archetypal nucleation-dependent aggregation mechanism. By digestion with trypsin or proteinase K and identification by mass spectrometry, we have determined that the region from Tyr(25) to Lys(86) is incorporated into the core of the fibrils. We suggest that this region, which is predicted to be aggregation-prone, accounts for the amyloidogenic nature of kappa-casein. Based on these data, we propose that fibril formation by RCMkappa-CN occurs through a novel mechanism whereby the rate-limiting step is the dissociation of an amyloidogenic precursor from an oligomeric state rather than the formation of stable nuclei, as has been described for most other fibril-forming systems.
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Affiliation(s)
- Heath Ecroyd
- School of Chemistry and the Physics, University of Adelaide, Adelaide, South Australia.
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17
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Mezzenga R, Schurtenberger P, Burbidge A, Michel M. Understanding foods as soft materials. NATURE MATERIALS 2005; 4:729-40. [PMID: 16195765 DOI: 10.1038/nmat1496] [Citation(s) in RCA: 436] [Impact Index Per Article: 22.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/04/2023]
Abstract
Foods make up some of the most complex examples of soft condensed matter (SCM) with which we interact daily. Their complexity arises from several factors: the intricacy of components, the different aggregation states in which foods are encountered, and the multitude of relevant characteristic time and length scales. Because foodstuffs are governed by the rules of SCM physics but with all the complications related to real systems, the experimental and theoretical approaches of SCM physics have deepened our comprehension of their nature and behaviour, but many questions remain. In this review we discuss the current understanding of food science, by considering established SCM methods as well as emerging techniques and theoretical approaches. With their complexity, heterogeneity and multitude of states, foods provide SCM physics with a challenge of remarkable importance.
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Affiliation(s)
- Raffaele Mezzenga
- Department of Physics, University of Fribourg, Perolles, Fribourg, CH-1700 Switzerland.
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18
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Farrell HM, Cooke PH, Wickham ED, Piotrowski EG, Hoagland PD. Environmental influences on bovine kappa-casein: reduction and conversion to fibrillar (amyloid) structures. JOURNAL OF PROTEIN CHEMISTRY 2003; 22:259-73. [PMID: 12962326 DOI: 10.1023/a:1025020503769] [Citation(s) in RCA: 96] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Abstract
The caseins of milk form a unique calcium-phosphate transport complex that provides these necessary nutrients to the neonate. The colloidal stability of these particles is primarily the result of kappa-casein. As purified from milk, this protein occurs as spherical particles with a weight average molecular weight of 1.18 million. The protein exhibits a unique disulfide bonding pattern, which (in the absence of reducing agents) ranges from monomer to octamers and above on SDS-PAGE. Severe heat treatment of the kappa-casein (90 degrees C) in the absence of SDS, before electrophoresis, caused an increase in the polymeric distribution: up to 40% randomly aggregated high-molecular weight polymers, presumably promoted by free sulfhydryl groups (J. Protein Chem. 17: 73-84, 1998). To ascertain the role of the sulfhydryl groups, the protein was reduced and carboxymethylated (RCM-K). Surprisingly, at only 37 degrees C, the RCM-kappa-casein exhibited an increase in weight average molecular weight and tendency to self-association when studied at 3000 rpm by analytical ultracentrifugation. Electron microscopy (EM) of the 37 degrees C RCM sample showed that, in addition to the spherical particles found in the native protein, there was a high proportion of fibrillar structures. The fibrillar structures were up to 600 nm in length. Circular dichroism (CD) spectroscopy was used to investigate the temperature-induced changes in the secondary structure of the native and RCM-kappa-caseins. These studies indicate that there was little change in the distribution of secondary structural elements during this transition, with extended strand and beta turns predominating. On the basis of three-dimensional molecular modeling predictions, there may exist a tyrosine-rich repeated sheet-turn-sheet motif in kappa-casein (residues 15-65), which may allow for the stacking of the molecules into fibrillar structures. Previous studies on amyloid proteins have suggested that such motifs promote fibril formation, and near-ultraviolet CD and thioflavin-T binding studies on RCM-kappa-casein support this concept. The results are discussed with respect to the role that such fibrils may play in the synthesis and secretion of casein micelles in lactating mammary gland.
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Affiliation(s)
- Harold M Farrell
- United States Department of Agriculture, ARS, Eastern Regional Research Center, Wyndmoor, Pennsylvania 19038, USA.
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19
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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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22
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Farrell HM, Wickham ED, Dower HJ, Piotrowski EG, Hoagland PD, Cooke PH, Groves ML. Characterization of the particles of purified kappa-casein: trypsin as a probe of surface-accessible residues. JOURNAL OF PROTEIN CHEMISTRY 1999; 18:637-52. [PMID: 10609639 DOI: 10.1023/a:1020698021899] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Abstract
kappa-Casein as purified from bovine milk exhibits a rather unique disulfide bonding pattern as revealed by SDS-PAGE. The disulfide-bonded caseins present range from dimer to octamer and above and preparations contain about 10% monomer. All of these heterogeneous polymers, however, self-associate into nearly spherical particles with an average diameter of 13 nm at pH 8.0, as revealed by negatively stained transmission electron micrographs and dynamic light scattering. The weight-average molecular weight of the aggregates at pH 8.0, as judged by analytical ultracentrifugation, is 648,000. Trypsin digestion at pH 8.0 was used to probe the surface groups of the kappa-casein A polymers. The reaction with trypsin was rapid and the peptides liberated were identified by separation with reverse-phase HPLC, amino acid analysis, and protein sequencing. The most rapidly released peptides (t1/2 < 30 sec) were from cleavage at Arg 97 and Lys residues 111 and 112. These results suggest a surface orientation for these residues, and the data are in accord with earlier proposed 3D predictive models for kappa-casein. It is speculated that Arg 97, together with adjacent His residues (98 and 100) and Lys residues 111 and 112, form two positively charged clusters on the surface of the otherwise negatively charged casein. These clusters bracket the neutral chymosin cleavage site (whose hydrolysis triggers a well-known digestive process) and so these clusters may facilitate docking of the substrate caseins with chymosin.
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Affiliation(s)
- H M Farrell
- USDA, ARS, Eastern Regional Research Center, Wyndmoor, Pennsylvania 19038, USA
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23
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Lehner D, Worning P, Fritz G, Øgendal L, Bauer R, Glatter O. Characterization of Enzymatically Induced Aggregation of Casein Micelles in Natural Concentration by in Situ Static Light Scattering and Ultra Low Shear Viscosimetry. J Colloid Interface Sci 1999; 213:445-456. [PMID: 10222086 DOI: 10.1006/jcis.1999.6124] [Citation(s) in RCA: 19] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
The aggregation of casein micelles in undiluted skim milk after the addition of chymosin was studied by static light scattering and ultra low shear viscometry. The static light scattering measurements were made with two different sample thicknesses, 72 and 16 µm. The scattering data were analyzed by indirect Fourier transformation and by the polydispersity inversion technique which led to pair distance distribution functions and size distribution function, respectively. The minimum scattering angle was 1 degrees, which allows for the determination of particle sizes up to a maximum diameter of 12 µm. The fractal dimension determined from double logarithmic plots of intensity versus scattering vector resulted in values between 1.9 and 2.0. The influence of multiple scattering was determined by comparison of the measurements with the different sample thicknesses. The measurements show no significant influence of multiple scattering when the transmission is above 0.85. Due to the very complex and porous structure of the casein aggregates the Rayleigh-Debye-Gans scattering theory has been used in the data analysis. Measurements with a new instrument using ultra low shear showed good agreement with theory. Copyright 1999 Academic Press.
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Affiliation(s)
- D Lehner
- Institute of Physical Chemistry, University of Graz, Heinrichstrasse 28, Graz, A-8010, Austria
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24
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Farrell H, Wickham E, Groves M. Environmental Influences on Purified κ-Casein: Disulfide Interactions. J Dairy Sci 1998. [DOI: 10.3168/jds.s0022-0302(98)75861-8] [Citation(s) in RCA: 24] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
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Abstract
During the last decade, marked progress has been made in the study of the fine details of the structures of milk proteins such as caseins, beta-lactoglobulin, alpha-lactalbumin, and lactotransferrin. Many of the functional properties of the individual milk proteins, as well as the milk protein products, may be described at the molecular level. This article is an attempt to thoroughly review the three-dimensional structures of major milk proteins, and to correlate them with the functional aspects of these proteins as food ingredients.
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Affiliation(s)
- D W Wong
- USDA-ARS-WRRC, Albany, California 94710, USA
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26
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Farrell HM, Kumosinski TF, Cooke PH, King G, Hoagland PD, Wickham ED, Dower HJ, Groves ML. Particle sizes of purified kappa-casein: metal effect and correspondence with predicted three-dimensional molecular models. JOURNAL OF PROTEIN CHEMISTRY 1996; 15:435-45. [PMID: 8895088 DOI: 10.1007/bf01886850] [Citation(s) in RCA: 26] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/02/2023]
Abstract
kappa-Casein as purified from bovine milk exhibits a rather unique disulfide bonding pattern as revealed by SDS-PAGE. The disulfide-bonded caseins present range from dimer to octamer and above and preparations contain about 10% monomer. All of these heterogenous polymers, however, self-associated into nearly spherical uniform particles with an average radius of 8.9 nm as revealed by negatively stained transmission electron micrographs. Evidence is presented that multivalent cations play a role in the stabilization of these spherical particles. Treatment with EDTA causes disruption of the kappa-casein particles and leads to a broder size distribution as judged by electron microscopy and dynamic light scattering. The size and shape of the particles are in accord with earlier proposed 3D models for kappa-casein that actually predicted participation of divalent cations in the structure.
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Affiliation(s)
- H M Farrell
- USDA, ARS, Eastern Regional Research Center, Wyndmoor, Pennsylvania 19038, USA
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