| 1. |
- Cragnell, Carolina, et al.
(författare)
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Dynamical Oligomerisation of Histidine Rich Intrinsically Disordered ProteinS Is Regulated through Zinc-Histidine Interactions
- 2019
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Ingår i: Biomolecules. - : MDPI AG. - 2218-273X. ; 9:5
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Tidskriftsartikel (refereegranskat)abstract
- Intrinsically disordered proteins (IDPs) can form functional oligomers and in some cases, insoluble disease related aggregates. It is therefore vital to understand processes and mechanisms that control pathway distribution. Divalent cations including Zn2+ can initiate IDP oligomerisation through the interaction with histidine residues but the mechanisms of doing so are far from understood. Here we apply a multi-disciplinary approach using small angle X-ray scattering, nuclear magnetic resonance spectroscopy, calorimetry and computations to show that that saliva protein Histatin 5 forms highly dynamic oligomers in the presence of Zn2+. The process is critically dependent upon interaction between Zn2+ ions and distinct histidine rich binding motifs which allows for thermodynamic switching between states. We propose a molecular mechanism of oligomerisation, which may be generally applicable to other histidine rich IDPs. Finally, as Histatin 5 is an important saliva component, we suggest that Zn2+ induced oligomerisation may be crucial for maintaining saliva homeostasis.
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| 2. |
- Fagerberg, Eric, et al.
(författare)
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Evaluating Models of Varying Complexity of Crowded Intrinsically Disordered Protein Solutions against SAXS
- 2019
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Ingår i: Journal of Chemical Theory and Computation. - : American Chemical Society (ACS). - 1549-9618 .- 1549-9626. ; 15:12, s. 6968-6983
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Tidskriftsartikel (refereegranskat)abstract
- Intrinsically disordered proteins (IDPs) adopt heterogeneous conformational ensembles in solution. The properties of the conformational ensemble are dependent upon the solution conditions, including the presence of ions, temperature, and crowding, and often directly impact biological function. Many in vitro investigations focus on the properties of IDPs under dilute conditions, rather than the crowded environment found in vivo. Due to their heterogeneous nature, the study of IDPs under crowded conditions is challenging both experimentally and computationally. Despite this, such studies are worth pursuing due to the insight gained into biologically relevant phenomena. Here, we study the highly charged IDP Histatin 5 under self-crowded conditions in low and high salt conditions. A combination of small-angle X-ray scattering and different simulation models, spanning a range of computational complexity and detail, is used. Most models are found to have limited application when compared to results from experiments. The best performing model is the highly coarse-grained, bead-necklace model. This model shows that Histatin 5 has a conserved radius of gyration and a decreasing flexibility with increasing protein concentration. Due to its computational efficiency, we propose that it is a suitable model to study crowded IDP solutions, despite its simplicity.
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| 3. |
- Jansson, Maria, et al.
(författare)
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Intercalation of cationic peptides within Laponite layered clay minerals in aqueous suspensions : The effect of stoichiometry and charge distance matching
- 2019
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Ingår i: Journal of Colloid and Interface Science. - : Elsevier BV. - 0021-9797. ; 557, s. 767-776
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Tidskriftsartikel (refereegranskat)abstract
- Clays can be synthesised to have specific functional properties, which have been exploited in a range of industrial processes. A key characteristic of clay is the presence of a negatively charged surface, surrounded by an oppositely charged rim. Because of that, clays are able to sequester cationic compounds resulting in the formation of ordered layered structures, known as tactoids. Recent research has highlighted the possibility of utilising clay as a drug delivery compound for cationic peptides. Here, we investigate the process of intercalation by using the highly cationic peptide deca-arginine, and the synthetic clay Laponite, in aqueous suspensions with 2.5 wt% Laponite, and varying peptide concentrations. Small-angle X-ray scattering experiments show that tactoids are formed as a function of deca-arginine concentration in the dispersion, and for an excess of peptide, i.e. above a matched charge-ratio between the peptide and clay, the growth of the tactoids is limited, resulting in tactoidal dissolution. Zeta-potential measurements confirm that the observed dissolution is caused by overcharging of the platelets. By employing coarse-grained molecular dynamics simulations based on the continuum model, we are able to predict the tactoid formation, the growth, and the dissolution, in agreement with experimental results. We propose that the present simulation method can be a useful tool to tune peptide and clay characteristics to optimise and determine the extent of intercalation by cationic peptides of therapeutic interest.
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| 4. |
- Lenton, Samuel, et al.
(författare)
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A review of the biology of calcium phosphate sequestration with special reference to milk.
- 2015
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Ingår i: Dairy Science & Technology. - : Springer Science and Business Media LLC. - 1958-5586 .- 1958-5594. ; 95:1, s. 3-14
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Forskningsöversikt (refereegranskat)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.
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| 5. |
- Lenton, Samuel, et al.
(författare)
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Effect of Phosphorylation on a Human-like Osteopontin Peptide
- 2017
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Ingår i: Biophysical Journal. - : Elsevier BV. - 0006-3495. ; 112:8, s. 1586-1596
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Tidskriftsartikel (refereegranskat)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.
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| 6. |
- Lenton, Samuel, et al.
(författare)
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Structural studies of hydrated samples of amorphous calcium phosphate and phosphoprotein nanoclusters.
- 2016
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Ingår i: European Biophysics Journal. - : Springer Science and Business Media LLC. - 1432-1017 .- 0175-7571.
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Tidskriftsartikel (refereegranskat)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.
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