1
|
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.
Collapse
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
| |
Collapse
|
2
|
Wang Q, Ma Y. Characterization of calcium phosphate nanoparticles sequestered by phosphopeptides in response to heat treatment. Lebensm Wiss Technol 2022. [DOI: 10.1016/j.lwt.2022.113816] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022]
|
3
|
Hettinga K, Bijl E. Can recombinant milk proteins replace those produced by animals? Curr Opin Biotechnol 2022; 75:102690. [PMID: 35104717 DOI: 10.1016/j.copbio.2022.102690] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/31/2021] [Revised: 12/13/2021] [Accepted: 01/15/2022] [Indexed: 11/03/2022]
Abstract
The consumption of animal proteins in general, and dairy proteins in particular, is associated with sustainability and animal welfare issues. Recombinant synthesis of milk proteins is therefore receiving increasing interest, with several studies showing synthesis of milk proteins using a wide range of expression systems. Achieving a high yield and purity is essential for economic production. Besides the synthesis, also the construction of the specific structure in which milk proteins are present in animal milks, casein micelles, is needed. Looking at the current state-of-the-art, the steps to produce recombinant dairy products are technically feasible, but whether it can be implemented at low cost, with the process being environmentally friendly, remains to be seen in the coming years.
Collapse
Affiliation(s)
- Kasper Hettinga
- Dairy Science & Technology, Food Quality and Design Group, Wageningen University & Research, 6708WG Wageningen, The Netherlands.
| | - Etske Bijl
- Dairy Science & Technology, Food Quality and Design Group, Wageningen University & Research, 6708WG Wageningen, The Netherlands
| |
Collapse
|
4
|
An assay of human tyrosine protein kinase ABL activity using an Escherichia coli protein expression system. Biotechniques 2021; 70:209-217. [PMID: 33820471 DOI: 10.2144/btn-2020-0154] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022] Open
Abstract
ABL, a human tyrosine protein kinase, and its substrate are co-expressed in Escherichia coli. Tyrosine phosphorylation of the substrate in E. coli was detected using Phos-tag SDS-PAGE. The bacterial co-expression system was used as a field for the kinase reaction to evaluate the enzymatic activity of five types of ABL kinase domain mutants. Relative to wild-type ABL, kinase activity was comparable in the H396P mutant, reduced in both Y253F and E255K mutants and undetectable in T315I and M351T mutants. These comparative results demonstrated that the phosphorylation states of the mutants correlated with their activity. The bacterial co-expression system permits rapid production of tyrosine kinase variants and provides a simple approach for examining their structure-activity relationships.
Collapse
|
5
|
Structural Biology of Calcium Phosphate Nanoclusters Sequestered by Phosphoproteins. CRYSTALS 2020. [DOI: 10.3390/cryst10090755] [Citation(s) in RCA: 15] [Impact Index Per Article: 3.8] [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.
Collapse
|
6
|
Carver JA, Holt C. Functional and dysfunctional folding, association and aggregation of caseins. PROTEIN MISFOLDING 2019; 118:163-216. [DOI: 10.1016/bs.apcsb.2019.09.002] [Citation(s) in RCA: 17] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/26/2022]
|
7
|
A quantitative model of the bovine casein micelle: ion equilibria and calcium phosphate sequestration by individual caseins in bovine milk. EUROPEAN BIOPHYSICS JOURNAL: EBJ 2018; 48:45-59. [PMID: 30128695 DOI: 10.1007/s00249-018-1330-2] [Citation(s) in RCA: 18] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/08/2018] [Revised: 08/02/2018] [Accepted: 08/13/2018] [Indexed: 10/28/2022]
Abstract
The white appearance of skim milk is due to strong light scattering by colloidal particles called casein micelles. Bovine casein micelles comprise expressed proteins from four casein genes together with significant fractions of the total calcium, inorganic phosphate, magnesium and citrate ions in the milk. Thus, the milk salts are partitioned between the casein micelles, where they are mostly in the form of nanoclusters of an amorphous calcium phosphate sequestered by caseins through their phosphorylated residues, with the remainder in the continuous phase. Previously, a salt partition calculation was made assuming that the nanoclusters are sequestered only by short, highly phosphorylated casein sequences, sometimes called phosphate centres. Three of the four caseins have a proportion of their phosphorylated residues in either one or two phosphate centres and these were proposed to react with the nanoclusters equally and independently. An improved model of the partition of caseins and salts in milk is described in which all the phosphorylated residues in competent caseins act together to bind to and sequester the nanoclusters. The new model has been applied to results from a recent study of variation in salt and casein composition in the milk of individual cows. Compared to the previous model, it provides better agreement with experiment of the partition of caseins between free and bound states and equally good results for the partition of milk salts. In addition, new calculations are presented for the charge on individual caseins in their bound and free states.
Collapse
|
8
|
Effect of Phosphorylation on a Human-like Osteopontin Peptide. Biophys J 2017; 112:1586-1596. [PMID: 28445750 PMCID: PMC5406370 DOI: 10.1016/j.bpj.2017.03.005] [Citation(s) in RCA: 19] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/09/2016] [Revised: 02/25/2017] [Accepted: 03/06/2017] [Indexed: 12/22/2022] Open
Abstract
The last decade established that the dynamic properties of the phosphoproteome are central to function and its modulation. The temporal dimension of phosphorylation effects remains nonetheless poorly understood, particularly for intrinsically disordered proteins. Osteopontin, selected for this study due to its key role in biomineralization, is expressed in many species and tissues to play a range of distinct roles. A notable property of highly phosphorylated isoforms of osteopontin is their ability to sequester nanoclusters of calcium phosphate to form a core-shell structure, in a fluid that is supersaturated but stable. In Biology, this process enables soft and hard tissues to coexist in the same organism with relative ease. Here, we extend our understanding of the effect of phosphorylation on a disordered protein, the recombinant human-like osteopontin rOPN. The solution structures of the phosphorylated and unphosphorylated rOPN were investigated by small-angle x-ray scattering and no significant changes were detected on the radius of gyration or maximum interatomic distance. The picosecond-to-nanosecond dynamics of the hydrated powders of the two rOPN forms were further compared by elastic and quasi-elastic incoherent neutron scattering. Phosphorylation was found to block some nanosecond side-chain motions while increasing the flexibility of other side chains on the faster timescale. Phosphorylation can thus selectively change the dynamic behavior of even a highly disordered protein such as osteopontin. Through such an effect on rOPN, phosphorylation can direct allosteric mechanisms, interactions with substrates, cofactors and, in this case, amorphous or crystalline biominerals.
Collapse
|
9
|
|
10
|
Lenton S, Nylander T, Holt C, Sawyer L, Härtlein M, Müller H, Teixeira SCM. Structural studies of hydrated samples of amorphous calcium phosphate and phosphoprotein nanoclusters. EUROPEAN BIOPHYSICS JOURNAL: EBJ 2016; 45:405-12. [PMID: 26780236 DOI: 10.1007/s00249-015-1109-7] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/27/2015] [Revised: 11/25/2015] [Accepted: 12/17/2015] [Indexed: 11/28/2022]
Abstract
There are abundant examples of nanoclusters and inorganic microcrystals in biology. Their study under physiologically relevant conditions remains challenging due to their heterogeneity, instability, and the requirements of sample preparation. Advantages of using neutron diffraction and contrast matching to characterize biomaterials are highlighted in this article. We have applied these and complementary techniques to search for nanocrystals within clusters of calcium phosphate sequestered by bovine phosphopeptides, derived from osteopontin or casein. The neutron diffraction patterns show broad features that could be consistent with hexagonal hydroxyapatite crystallites smaller than 18.9 Å. Such nanocrystallites are, however, undetected by the complementary X-ray and FTIR data, collected on the same samples. The absence of a distinct diffraction pattern from the nanoclusters supports the generally accepted amorphous calcium phosphate structure of the mineral core.
Collapse
Affiliation(s)
- Samuel Lenton
- EPSAM, Keele University, Staffordshire, ST5 5BG, UK.,Institut Laue-Langevin, 71 Avenue des Martyrs, 38042, Grenoble Cedex 9, France.,School of Physics and Astronomy, Astbury Center for Structural Molecular Biology, University of Leeds, LS2 9JT, Leeds, UK
| | - Tommy Nylander
- Division of Physical Chemistry, Department of Chemistry, Lund University, 124, Lund, S221 00, Sweden
| | - Carl Holt
- Institute of Molecular, Cell, and Systems Biology, University of Glasgow, Glasgow, G12 8QQ, UK
| | - Lindsay Sawyer
- Structural Biochemistry Group, University of Edinburgh, Roger Land Building, The King's Buildings, Mayfield Road, EH9 3JR, Edinburgh, UK
| | - Michael Härtlein
- Institut Laue-Langevin, 71 Avenue des Martyrs, 38042, Grenoble Cedex 9, France
| | - Harrald Müller
- European Synchrotron Radiation Facility, CS 40220, 38043, Grenoble, France
| | - Susana C M Teixeira
- EPSAM, Keele University, Staffordshire, ST5 5BG, UK. .,Institut Laue-Langevin, 71 Avenue des Martyrs, 38042, Grenoble Cedex 9, France.
| |
Collapse
|
11
|
Lenton S, Seydel T, Nylander T, Holt C, Härtlein M, Teixeira S, Zaccai G. Dynamic footprint of sequestration in the molecular fluctuations of osteopontin. J R Soc Interface 2015; 12:0506. [PMID: 26354827 PMCID: PMC4614460 DOI: 10.1098/rsif.2015.0506] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/04/2015] [Accepted: 08/19/2015] [Indexed: 11/12/2022] Open
Abstract
The sequestration of calcium phosphate by unfolded proteins is fundamental to the stabilization of biofluids supersaturated with respect to hydroxyapatite, such as milk, blood or urine. The unfolded state of osteopontin (OPN) is thought to be a prerequisite for this activity, which leads to the formation of core-shell calcium phosphate nanoclusters. We report on the structures and dynamics of a native OPN peptide from bovine milk, studied by neutron spectroscopy and small-angle X-ray and neutron scattering. The effects of sequestration are quantified on the nanosecond- ångström resolution by elastic incoherent neutron scattering. The molecular fluctuations of the free phosphopeptide are in agreement with a highly flexible protein. An increased resilience to diffusive motions of OPN is corroborated by molecular fluctuations similar to those observed for globular proteins, yet retaining conformational flexibilities. The results bring insight into the modulation of the activity of OPN and phosphopeptides with a role in the control of biomineralization. The quantification of such effects provides an important handle for the future design of new peptides based on the dynamics-activity relationship.
Collapse
Affiliation(s)
- S Lenton
- Institut Laue-Langevin, 71 Avenue des Martyrs, 38042 Grenoble cedex 9, France Environment, Physical Sciences and Applied Mathematics Research Institute, Keele University, Staffordshire ST5 5BG, UK
| | - T Seydel
- Institut Laue-Langevin, 71 Avenue des Martyrs, 38042 Grenoble cedex 9, France
| | - T Nylander
- Division of Physical Chemistry, Lund University, PO Box 124, 221 00 Lund, Sweden
| | - C Holt
- Institute of Molecular, Cell and Systems Biology, University of Glasgow, Glasgow G12 8QQ, UK
| | - M Härtlein
- Institut Laue-Langevin, 71 Avenue des Martyrs, 38042 Grenoble cedex 9, France
| | - S Teixeira
- Institut Laue-Langevin, 71 Avenue des Martyrs, 38042 Grenoble cedex 9, France Environment, Physical Sciences and Applied Mathematics Research Institute, Keele University, Staffordshire ST5 5BG, UK
| | - G Zaccai
- Institut Laue-Langevin, 71 Avenue des Martyrs, 38042 Grenoble cedex 9, France C.N.R.S., Institut de Biologie Structurale, F-38044 Grenoble, France
| |
Collapse
|
12
|
|
13
|
A review of the biology of calcium phosphate sequestration with special reference to milk. ACTA ACUST UNITED AC 2014; 95:3-14. [PMID: 25632319 PMCID: PMC4302223 DOI: 10.1007/s13594-014-0177-2] [Citation(s) in RCA: 33] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/14/2014] [Revised: 06/05/2014] [Accepted: 06/17/2014] [Indexed: 11/04/2022]
Abstract
In milk, a stable fluid is formed in which sequestered nanoclusters of calcium phosphate are substructures in casein micelles. As a result, calcium and phosphate concentrations in milk can be far in excess of their solubility. Variations of calcium, phosphate and casein concentrations in milks, both within and among species, are mainly due to the formation of the nanocluster complexes. Caseins evolved from tooth and bone proteins well before the evolution of lactation. It has therefore been suggested that the role of caseins in milk is an adaptation of an antecedent function in the control of some aspect of biomineralisation. There is new evidence that nanocluster-type complexes are also present in blood serum and, by implication, in many other closely related biofluids. Because such fluids are stable but nevertheless supersaturated with respect to the bone and tooth mineral hydroxyapatite, they allow soft and mineralised tissues to co-exist in the same organism with relative ease. An appreciable concentration of nanocluster complexes exists in fresh saliva. Such saliva may stabilise tooth mineral and help to repair demineralised lesions. In the extracellular matrix of bone, nanocluster complexes may be involved in directing the amorphous calcium phosphate to intrafibrillar spaces in collagen where they can mature into oriented apatite crystals. Thus, evidence is accumulating that calcium phosphate sequestration by phosphopeptides to form equilibrium complexes, first observed in milk, is more generally important in the control of physiological calcification.
Collapse
|
14
|
Holt C, Lenton S, Nylander T, Sørensen ES, Teixeira SC. Mineralisation of soft and hard tissues and the stability of biofluids. J Struct Biol 2014; 185:383-96. [DOI: 10.1016/j.jsb.2013.11.009] [Citation(s) in RCA: 47] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/29/2013] [Revised: 11/29/2013] [Accepted: 11/30/2013] [Indexed: 02/04/2023]
|
15
|
Holt C. Unfolded phosphopolypeptides enable soft and hard tissues to coexist in the same organism with relative ease. Curr Opin Struct Biol 2013; 23:420-5. [DOI: 10.1016/j.sbi.2013.02.010] [Citation(s) in RCA: 33] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/27/2012] [Revised: 02/21/2013] [Accepted: 02/26/2013] [Indexed: 12/11/2022]
|
16
|
Kotzsch A, Vernet E, Hammarström M, Berthelsen J, Weigelt J, Gräslund S, Sundström M. A secretory system for bacterial production of high-profile protein targets. Protein Sci 2011; 20:597-609. [PMID: 21308845 DOI: 10.1002/pro.593] [Citation(s) in RCA: 35] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023]
Abstract
Escherichia coli represents a robust, inexpensive expression host for the production of recombinant proteins. However, one major limitation is that certain protein classes do not express well in a biologically relevant form using standard expression approaches in the cytoplasm of E. coli. To improve the usefulness of the E. coli expression platform we have investigated combinations of promoters and selected N-terminal fusion tags for the extracellular expression of human target proteins. A comparative study was conducted on 24 target proteins fused to outer membrane protein A (OmpA), outer membrane protein F (OmpF) and osmotically inducible protein Y (OsmY). Based on the results of this initial study, we carried out an extended expression screen employing the OsmY fusion and multiple constructs of a more diverse set of human proteins. Using this high-throughput compatible system, we clearly demonstrate that secreted biomedically relevant human proteins can be efficiently retrieved and purified from the growth medium.
Collapse
Affiliation(s)
- Alexander Kotzsch
- Facility for Protein Science and Technology, The Novo Nordisk Foundation Center for Protein Research, Faculty of Health Sciences, University of Copenhagen, Blegdamsvej 3B, 2200 Copenhagen N, Denmark.
| | | | | | | | | | | | | |
Collapse
|