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Raynes JK, Mata J, Wilde KL, Carver JA, Kelly SM, Holt C. Structure of biomimetic casein micelles: Critical tests of the hydrophobic colloid and multivalent-binding models using recombinant deuterated and phosphorylated β-casein. J Struct Biol X 2024; 9:100096. [PMID: 38318529 PMCID: PMC10840362 DOI: 10.1016/j.yjsbx.2024.100096] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/19/2023] [Revised: 01/08/2024] [Accepted: 01/17/2024] [Indexed: 02/07/2024] Open
Abstract
Milk contains high concentrations of amyloidogenic casein proteins and is supersaturated with respect to crystalline calcium phosphates such as apatite. Nevertheless, the mammary gland normally remains unmineralized and free of amyloid. Unlike κ-casein, β- and αS-caseins are highly effective mineral chaperones that prevent ectopic and pathological calcification of the mammary gland. Milk invariably contains a mixture of two to five different caseins that act on each other as molecular chaperones. Instead of forming amyloid fibrils, several thousand caseins and hundreds of nanoclusters of amorphous calcium phosphate combine to form fuzzy complexes called casein micelles. To understand the biological functions of the casein micelle its structure needs to be understood better than at present. The location in micelles of the highly amyloidogenic κ-casein is disputed. In traditional hydrophobic colloid models, it, alone, forms a stabilizing surface coat that also determines the average size of the micelles. In the recent multivalent-binding model, κ-casein is present throughout the micelle, in intimate contact with the other caseins. To discriminate between these models, a range of biomimetic micelles was prepared using a fixed concentration of the mineral chaperone β-casein and nanoclusters of calcium phosphate, with variable concentrations of κ-casein. A biomimetic micelle was also prepared using a highly deuterated and in vivo phosphorylated recombinant β-casein with calcium phosphate and unlabelled κ-casein. Neutron and X-ray scattering experiments revealed that κ-casein is distributed throughout the micelle, in quantitative agreement with the multivalent-binding model but contrary to the hydrophobic colloid models.
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Affiliation(s)
- Jared K. Raynes
- CSIRO Agriculture & Food, 671 Sneydes Road, Werribee, VIC 3031, Australia
- All G Foods, Waterloo, NSW 2006, Australia
| | - Jitendra Mata
- Australian Centre for Neutron Scattering, Australian Nuclear Science and Technology Organisation, Lucas Heights, NSW 2234, Australia
- School of Chemistry, University of New South Wales, Sydney 2052, Australia
| | - Karyn L. Wilde
- National Deuteration Facility, Australian Nuclear Science and Technology Organisation, Lucas Heights, NSW 2234, Australia
| | - John A. Carver
- Research School of Chemistry, The Australian National University, Acton, ACT 2601, Australia
| | - Sharon M. Kelly
- School of Molecular Biosciences, University of Glasgow, Glasgow G12 8QQ, United Kingdom
| | - Carl Holt
- School of Molecular Biosciences, University of Glasgow, Glasgow G12 8QQ, United Kingdom
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Zeng X, Ding Y, Zhang Y, Uddin MR, Dabouei A, Xu M. DUAL: deep unsupervised simultaneous simulation and denoising for cryo-electron tomography. BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2024:2024.03.02.583135. [PMID: 38496657 PMCID: PMC10942334 DOI: 10.1101/2024.03.02.583135] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 03/19/2024]
Abstract
Recent biotechnological developments in cryo-electron tomography allow direct visualization of native sub-cellular structures with unprecedented details and provide essential information on protein functions/dysfunctions. Denoising can enhance the visualization of protein structures and distributions. Automatic annotation via data simulation can ameliorate the time-consuming manual labeling of large-scale datasets. Here, we combine the two major cryo-ET tasks together in DUAL, by a specific cyclic generative adversarial network with novel noise disentanglement. This enables end-to-end unsupervised learning that requires no labeled data for training. The denoising branch outperforms existing works and substantially improves downstream particle picking accuracy on benchmark datasets. The simulation branch provides learning-based cryo-ET simulation for the first time and generates synthetic tomograms indistinguishable from experimental ones. Through comprehensive evaluations, we showcase the effectiveness of DUAL in detecting macromolecular complexes across a wide range of molecular weights in experimental datasets. The versatility of DUAL is expected to empower cryo-ET researchers by improving visual interpretability, enhancing structural detection accuracy, expediting annotation processes, facilitating cross-domain model adaptability, and compensating for missing wedge artifacts. Our work represents a significant advancement in the unsupervised mining of protein structures in cryo-ET, offering a multifaceted tool that facilitates cryo-ET research.
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Affiliation(s)
- Xiangrui Zeng
- Ray and Stephanie Lane Computational Biology Department, Carnegie Mellon University, Pittsburgh, PA, 15213, USA
| | - Yizhe Ding
- Department of Statistics, The Pennsylvania State University, University Park, PA, 16802, USA
| | - Yueqian Zhang
- School of Electrical and Electronic Engineering, Nanyang Technological University, 50 Nanyang Avenue, Singapore, 639798, Singapore
| | - Mostofa Rafid Uddin
- Ray and Stephanie Lane Computational Biology Department, Carnegie Mellon University, Pittsburgh, PA, 15213, USA
| | - Ali Dabouei
- Ray and Stephanie Lane Computational Biology Department, Carnegie Mellon University, Pittsburgh, PA, 15213, USA
| | - Min Xu
- Ray and Stephanie Lane Computational Biology Department, Carnegie Mellon University, Pittsburgh, PA, 15213, USA
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Runthala A, Mbye M, Ayyash M, Xu Y, Kamal-Eldin A. Caseins: Versatility of Their Micellar Organization in Relation to the Functional and Nutritional Properties of Milk. Molecules 2023; 28:molecules28052023. [PMID: 36903269 PMCID: PMC10004547 DOI: 10.3390/molecules28052023] [Citation(s) in RCA: 5] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/27/2022] [Revised: 02/10/2023] [Accepted: 02/11/2023] [Indexed: 02/24/2023] Open
Abstract
The milk of mammals is a complex fluid mixture of various proteins, minerals, lipids, and other micronutrients that play a critical role in providing nutrition and immunity to newborns. Casein proteins together with calcium phosphate form large colloidal particles, called casein micelles. Caseins and their micelles have received great scientific interest, but their versatility and role in the functional and nutritional properties of milk from different animal species are not fully understood. Caseins belong to a class of proteins that exhibit open and flexible conformations. Here, we discuss the key features that maintain the structures of the protein sequences in four selected animal species: cow, camel, human, and African elephant. The primary sequences of these proteins and their posttranslational modifications (phosphorylation and glycosylation) that determine their secondary structures have distinctively evolved in these different animal species, leading to differences in their structural, functional, and nutritional properties. The variability in the structures of milk caseins influence the properties of their dairy products, such as cheese and yogurt, as well as their digestibility and allergic properties. Such differences are beneficial to the development of different functionally improved casein molecules with variable biological and industrial utilities.
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Affiliation(s)
- Ashish Runthala
- Department of Biotechnology, Koneru Lakshmaiah Education Foundation, Vijayawada 522302, India
- Correspondence: (A.R.); (A.K.-E.); Tel.: +971-5-0138-9248 (A.K.-E.)
| | - Mustapha Mbye
- Department of Food Science, United Arab Emirates University, Al Ain P.O. Box 15551, United Arab Emirates
| | - Mutamed Ayyash
- Department of Food Science, United Arab Emirates University, Al Ain P.O. Box 15551, United Arab Emirates
| | - Yajun Xu
- Department of Nutrition and Food Hygiene, School of Public Health, Peking University, Beijing 100871, China
| | - Afaf Kamal-Eldin
- Department of Food Science, United Arab Emirates University, Al Ain P.O. Box 15551, United Arab Emirates
- Zayed Bin Sultan Center for Health Sciences, United Arab Emirates University, Al Ain P.O. Box 15551, United Arab Emirates
- Correspondence: (A.R.); (A.K.-E.); Tel.: +971-5-0138-9248 (A.K.-E.)
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Pedersen JS, Møller TL, Raak N, Corredig M. A model on an absolute scale for the small-angle X-ray scattering from bovine casein micelles. SOFT MATTER 2022; 18:8613-8625. [PMID: 36331028 DOI: 10.1039/d2sm00724j] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/16/2023]
Abstract
Casein micelles extracted from milk are 100-400 nm-sized particles, made up of proteins and calcium phosphates, with the latter as colloidal calcium phosphate particles (CCPs) in a size range of 2-4 nm embedded in a protein network. The hierarchical structures give rise to a variation of scattering intensity over many orders of magnitude, which can be measured by small-angle X-ray scattering and static light scattering. Expressions for the scattering intensity of a general simple model for composite particles with polydispersities of overall size and subparticles are derived, and some approximations are checked by generating scattering data for systems generated by Monte Carlo simulations. Based on the simpler models, a new model has been developed for casein micelles, where the scattering is expressed on an absolute scale and where the concentrations of, respectively, protein and CCPs are used as constraints, providing a consistent model. The CCPs are modelled as oblate ellipsoids and the protein as star structures. Correlations between the substructures of CCPs and protein structures are taken into account in terms of partial structure factors. The overall structure as well as some heterogeneities at intermediate length scale are modelled as polydisperse spheres. The model fits the data very well on all length scales and demonstrates that both the scattering from CCPs and protein is important. Thus, the model provides a detailed description of the casein structure, which is consistent with the information available in the literature.
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Affiliation(s)
- Jan Skov Pedersen
- Department of Chemistry and Interdisciplinary Nanoscience Center (iNANO), Aarhus University, Gustav Wieds Vej 14, 8000 Aarhus C, Denmark.
| | - Thea Lykkegaard Møller
- Department of Food Science, CiFOOD Center for Innovative Food Research, Aarhus University, Agro Food Park 48, 8200 Aarhus N, Denmark
| | - Norbert Raak
- Department of Food Science, CiFOOD Center for Innovative Food Research, Aarhus University, Agro Food Park 48, 8200 Aarhus N, Denmark
| | - Milena Corredig
- Department of Food Science, CiFOOD Center for Innovative Food Research, Aarhus University, Agro Food Park 48, 8200 Aarhus N, Denmark
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Quantitative multivalent binding model of the structure, size distribution and composition of the casein micelles of cow milk. Int Dairy J 2022. [DOI: 10.1016/j.idairyj.2021.105292] [Citation(s) in RCA: 7] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
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Holt C. A quantitative calcium phosphate nanocluster model of the casein micelle: the average size, size distribution and surface properties. EUROPEAN BIOPHYSICS JOURNAL: EBJ 2021; 50:847-866. [PMID: 33866398 DOI: 10.1007/s00249-021-01533-5] [Citation(s) in RCA: 11] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/20/2020] [Revised: 01/22/2021] [Accepted: 03/28/2021] [Indexed: 10/21/2022]
Abstract
Caseins (αS1, αS2, β and κ) are the main protein fraction of bovine milk. Together with nanoclusters of amorphous calcium phosphate (CaP) and divalent cations, they combine to form a polydisperse distribution of particles called casein micelles. A casein micelle model is proposed which is consistent with the way in which intrinsically disordered proteins interact through predominantly polar, short, linear, motifs. Using the model, an expression is derived for the size distribution of casein micelles formed when caseins bind to the CaP nanoclusters and the complexes further associate with each other and the remaining mixture of free caseins. The result is a refined coat-core model in which the core is formed mainly by the nanocluster complexes and the coat is formed exclusively by the free caseins. Example calculations of the size distribution and surface composition of an average bovine milk are compared with experiment. The average size, size distribution and surface composition of the micelles is shown to depend on the affinity of the nanocluster complexes for each other in competition with their affinity for free caseins, and on the concentrations of free caseins, calcium ions and other salts in the continuous phase.
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Affiliation(s)
- Carl Holt
- Institute of Molecular, Cell and Systems Biology, University of Glasgow, Glasgow, G12 8QQ, UK.
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Wang Q, Holt C, Nylander T, Ma Y. Salt partition, ion equilibria, and the structure, composition, and solubility of micellar calcium phosphate in bovine milk with added calcium salts. J Dairy Sci 2020; 103:9893-9905. [DOI: 10.3168/jds.2020-18829] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/03/2020] [Accepted: 07/06/2020] [Indexed: 01/26/2023]
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Structural Biology of Calcium Phosphate Nanoclusters Sequestered by Phosphoproteins. CRYSTALS 2020. [DOI: 10.3390/cryst10090755] [Citation(s) in RCA: 19] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/24/2022]
Abstract
Biofluids that contain stable calcium phosphate nanoclusters sequestered by phosphopeptides make it possible for soft and hard tissues to co-exist in the same organism with relative ease. The stability diagram of a solution of nanocluster complexes shows how the minimum concentration of phosphopeptide needed for stability increases with pH. In the stable region, amorphous calcium phosphate cannot precipitate. Nevertheless, if the solution is brought into contact with hydroxyapatite, the crystalline phase will grow at the expense of the nanocluster complexes. The physico-chemical principles governing the formation, composition, size, structure, and stability of the complexes are described. Examples are given of complexes formed by casein, osteopontin, and recombinant phosphopeptides. Application of these principles and properties to blood serum, milk, urine, and resting saliva is described to show that under physiological conditions they are in the stable region of their stability diagram and so cannot cause soft tissue calcification. Stimulated saliva, however, is in the metastable region, consistent with its role in tooth remineralization. Destabilization of biofluids, with consequential ill-effects, can occur when there is a failure of homeostasis, such as an increase in pH without a balancing increase in the concentration of sequestering phosphopeptides.
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