| 1. |
- Fagerberg, Eric, et al.
(författare)
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Self-Diffusive Properties of the Intrinsically Disordered Protein Histatin 5 and the Impact of Crowding Thereon : A Combined Neutron Spectroscopy and Molecular Dynamics Simulation Study
- 2021
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Ingår i: Journal of Physical Chemistry B. - : American Chemical Society (ACS). - 1520-6106 .- 1520-5207.
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Tidskriftsartikel (refereegranskat)abstract
- Intrinsically disordered proteins (IDPs) are proteins that, in comparison with globular/structured proteins, lack a distinct tertiary structure. Here, we use the model IDP, Histatin 5, for studying its dynamical properties under self-crowding conditions with quasi-elastic neutron scattering in combination with full atomistic molecular dynamics (MD) simulations. The aim is to determine the effects of crowding on the center-of-mass diffusion as well as the internal diffusive behavior. The diffusion was found to decrease significantly, which we hypothesize can be attributed to some degree of aggregation at higher protein concentrations, (≥100 mg/mL), as indicated by recent small-angle X-ray scattering studies. Temperature effects are also considered and found to, largely, follow Stokes-Einstein behavior. Simple geometric considerations fail to accurately predict the rates of diffusion, while simulations show semiquantitative agreement with experiments, dependent on assumptions of the ratio between translational and rotational diffusion. A scaling law that previously was found to successfully describe the behavior of globular proteins was found to be inadequate for the IDP, Histatin 5. Analysis of the MD simulations show that the width of the distribution with respect to diffusion is not a simplistic mirroring of the distribution of radius of gyration, hence, displaying the particular features of IDPs that need to be accounted for.
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| 2. |
- Fagerberg, Eric, et al.
(författare)
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The Effects of Chain Length on the Structural Properties of Intrinsically Disordered Proteins in Concentrated Solutions
- 2021
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Ingår i: Journal of Physical Chemistry B. - : American Chemical Society (ACS). - 1520-6106 .- 1520-5207. ; 124:52, s. 11843-11853
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Tidskriftsartikel (refereegranskat)abstract
- Intrinsically disordered proteins (IDP) are proteins that sample a heterogeneous ensemble of conformers in solution. An estimated 25-30% of all eukaryotic proteins belong to this class. In vivo, IDPs function under conditions that are highly crowded by other biological macromolecules. Previous research has highlighted that the presence of crowding agents can influence the conformational ensemble sampled by IDPs, resulting in either compaction or expansion. The effects of self-crowding of the disordered protein Histatin 5 has, in an earlier study, been found to have limited influence on the conformational ensemble. In this study, it is examined whether the short chain length of Histatin 5 can explain the limited effects of crowding observed, by introducing (Histatin 5)2, a tandem repeat of Histatin 5. By utilizing small-angle X-ray scattering, it is shown that the conformational ensemble is conserved at high protein concentrations, in resemblance with Histatin 5, although with a lowered protein concentration at which aggregation arises. Under dilute conditions, atomistic molecular dynamics and coarse-grained Monte Carlo simulations, as well as an established scaling law, predicted more extended conformations than indicated by experimental data, hence implying that (Histatin 5)2 does not behave as a self-avoiding random walk.
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| 3. |
- Lenton, Samuel, et al.
(författare)
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From dilute to concentrated solutions of intrinsically disordered proteins : Interpretation and analysis of collected data
- 2023
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Ingår i: Small Angle Scattering Part B: Methods for Structural Interpretation. - : Elsevier. - 0076-6879 .- 1557-7988. - 9780323991810 ; 678, s. 299-330
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Bokkapitel (refereegranskat)abstract
- Intrinsically disordered proteins (IDPs) have a broad energy landscape and consequently sample many different conformations in solution. The innate flexibility of IDPs is exploited in their biological function, and in many instances allows a single IDP to regulate a range of processes in vivo. Due to their highly flexible nature, characterizing the structural properties of IDPs is not straightforward. Often solution-based methods such as Nuclear Magnetic Resonance (NMR), Förster Resonance Energy Transfer (FRET), and Small-Angle X-ray Scattering (SAXS) are used. SAXS is indeed a powerful technique to study the structural and conformational properties of IDPs in solution, and from the obtained SAXS spectra, information about the average size, shape, and extent of oligomerization can be determined. In this chapter, we will introduce model-free methods that can be used to interpret SAXS data and introduce methods that can be used to interpret SAXS data beyond analytical models, for example, by using atomistic and different levels of coarse-grained models in combination with molecular dynamics (MD) and Monte Carlo simulations.
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| 4. |
- Lenton, Samuel, et al.
(författare)
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From dilute to concentrated solutions of intrinsically disordered proteins: Sample preparation and data collection
- 2022
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Ingår i: Methods in Enzymology. - : Elsevier. - 0076-6879. ; 677, s. 457-478
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Bokkapitel (refereegranskat)abstract
- It is well-known that an increasing proportion of proteins, protein regions, and partners of globular proteins are being recognized as having an intrinsic disorder, and therefore, not adopting a single three-dimensional structure in solution. For these proteins, small-angle X-ray scattering (SAXS) has become a premier method for examination, since it can provide information about the ensemble of the structural conformations as well as the intermolecular interactions. SAXS measurements can be performed from low to high protein concentrations under different physicochemical properties of the solution. The focus of this chapter is to introduce the basics of how to use SAXS for protein samples, for new and less experienced users, in a simple and concise manner, with emphasis on highly flexible proteins and regions. Methodological aspects in the sample preparation, experiment design, and data collection stages are raised that should be considered prior to attempting SAXS experiments. This is to ensure that high-quality SAXS data is obtained that enables accurate analysis. However, many of the points raised will also be worth considering for SAXS experiments of globular proteins.
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| 5. |
- Lenton, Samuel, et al.
(författare)
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Impact of arginine−phosphate interactions on the reentrant condensation of disordered proteins
- 2021
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Ingår i: Biomacromolecules. - : American Chemical Society (ACS). - 1525-7797 .- 1526-4602. ; 22:4, s. 1532-1544
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Tidskriftsartikel (refereegranskat)abstract
- Re-entrant condensation results in the formation of a condensed protein regime between two critical ion concentrations. The process is driven by neutralization and inversion of the protein charge by oppositely charged ions. Re-entrant condensation of cationic proteins by the polyvalent anions, pyrophosphate and tripolyphosphate, has previously been observed, but not for citrate, which has similar charge and size compared to the polyphosphates. Therefore, besides electrostatic interactions, other specific interactions between the polyphosphate ions and proteins must contribute. Here, we show that additional., attractive interactions between arginine and tripolyphosphate determine the re-entrant condensation and decondensation boundaries of the cationic, intrinsically disordered saliva protein, histatin 5. Furthermore, we show by small-angle X-ray scattering (SAXS) that polyvalent anions cause compaction of histatin 5, as would be expected based solely on electrostatic interactions. Hence, we conclude that arginine−phosphate-specific interactions not only regulate solution properties but also influence the conformational ensemble of histatin 5, which is shown to vary with the number of arginine residues. Together, the results presented here provide further insight into an organizational mechanism that can be used to tune protein interactions in solution of both naturally occurring and synthetic proteins.
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| 6. |
- Lenton, Samuel, et al.
(författare)
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Structural biology of calcium phosphate nanoclusters sequestered by phosphoproteins
- 2020
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Ingår i: Crystals. - : MDPI AG. - 2073-4352. ; 10:9
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Forskningsöversikt (refereegranskat)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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