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| 2. |
- Berts, Ida, 1984-, et al.
(author)
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Controlling adsorption of albumin with hyaluronan on silica surfaces and sulfonated latex particles
- 2017
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In: Journal of Colloid and Interface Science. - : Elsevier BV. - 0021-9797 .- 1095-7103. ; 504, s. 315-324
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Journal article (peer-reviewed)abstract
- Polysaccharides are known to modify binding of proteins at interfaces and this paper describes studies of these interactions and how they are modified by pH. Specifically, the adsorption of human serum albumin on to polystyrene latex and to silica is described, focusing on how this is affected by hyaluronan. Experiments were designed to test how such binding might be modified under relevant physiological conditions. Changes in adsorption of albumin alone and the co-adsorption of albumin and hyaluronan are driven by electrostatic interactions. Multilayer binding is found to be regulated by the pH of the solution and the molecular mass and concentration of hyaluronan. Highest adsorption was observed at pH below 4.8 and for low molecular mass hyaluronan (<= 150 kDa) at concentrations above 2 mg ml(-1). On silica with grafted hyaluronan, albumin absorption is reversed by changes in solvent pH due to their strong electrostatic attraction. Albumin physisorbed on silica surfaces is also rinsed away with dilute hyaluronan solution at pH 4.8. The results demonstrate that the protein adsorption can be controlled both by changes of pH and by interaction with other biological macromolecules.
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| 3. |
- Berts, Ida, et al.
(author)
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Polymeric Smart Coating Strategy for Titanium Implants
- 2014
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In: Advanced Engineering Materials. - : Wiley. - 1438-1656 .- 1527-2648. ; 16:11, s. 1340-1350
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Journal article (peer-reviewed)abstract
- Hyaluronan based hydrogel coatings can mimic extracellular matrix components and incorporate growth factors that can be released during a progressive degradation while new tissue regenerates. This paper describes a structural characterization of a hydrogel coating made of modified hyaluronan polymers and how these coatings interact with bone morphogenetic protein-2 (BMP-2). Quartz crystal microbalance and neutron reflectivity measurements were used for in-situ, real-time measurements of the adsorption properties of polymers and proteins on smooth titanium oxide surfaces that mimic implant products in orthopedics. The adsorption of BMP-2 on a bare titanium oxide surface is compared to that on titanium oxide coated with different chemically modified hyaluronan, the most important being hyaluronan with bisphosphonate groups (HA-BP). The subsequent release of the BMP-2 from these hydrogel coatings could be triggered by calcium ions. The amount of adsorbed protein on the surfaces as well as the amount of released protein both depend on the type of hyaluronan coating. We conclude that HA-BP coated titanium oxide surfaces provide an excellent material for growth factor delivery in-vivo.
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| 4. |
- Berts, Ida, 1984-
(author)
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Relating the Bulk and Interface Structure of Hyaluronan to Physical Properties of Future Biomaterials
- 2013
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Doctoral thesis (other academic/artistic)abstract
- This dissertation describes a structural investigation of hyaluronan (HA) with neutron scattering techniques. HA is a natural biopolymer and one of the major components of the extracellular matrix, synovial fluid, and vitreous humor. It is used in several biomedical applications like tissue engineering, drug delivery, and treatment of osteoarthritis. Although HA is extensively studied, very little is known about its three-dimensional conformation and how it interacts with ions and other molecules. The study aims to understand the bulk structure of a cross-linked HA hydrogel, as well as the conformational arrangement of HA at solid-liquid interfaces. In addition, the structural changes of HA are investigated by simulation of physiological environments, such as changes in ions, interactions with nanoparticles, and proteins etc. Small-angle neutron scattering and neutron reflectivity are the two main techniques applied to investigate the nanostructure of hyaluronan in its original, hydrated state.The present study on hydrogels shows that they possess inhomogeneous structures best described with two correlation lengths, one of the order of a few nanometers and the other in the order of few hundred nanometers. These gels are made up of dense polymer-rich clusters linked to each other. The polymer concentration and mixing governs the connectivity between these clusters, which in turn determines the viscoelastic properties of the gels. Surface-tethered HA at a solid-liquid interface is best described with a smooth varying density profile. The shape of this profile depends on the immobilization chemistry, the deposition protocol, and the ionic interactions. HA could be suitably modified to enhance adherence to metal surfaces, as well as incorporation of proteins like growth factors with tunable release properties. This could be exploited for surface coating of implants with bioactive molecules. The knowledge gained from this work would significantly help to develop future biomaterials and surface coatings of implants and biomedical devices.
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| 5. |
- Berts, Ida, et al.
(author)
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Tuning the density profile of surface-grafted hyaluronan and the effect of counter-ions
- 2013
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In: European Physical Journal E. - : Springer Science and Business Media LLC. - 1292-8941 .- 1292-895X. ; 36:7, s. 70-
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Journal article (peer-reviewed)abstract
- The present paper investigates the structure and composition of grafted sodium hyaluronanat a solid-liquid interface using neutron reflection. The solvated polymer at the surface could be described with a density profile that decays exponentially towards the bulk solution. The density profileof the polymer varied depending on the deposition protocol. A single-stage deposition resulted in denser polymer layers, while layers created with a two-stage deposition process were more diffuse and had an overall lower density. Despite the diffuse density profile, two-stage deposition leads to a highersurface excess. Addition of calcium ions causes a strong collapse of the sodium hyaluronan chains, increasing the polymer density near the surface. This effect is more pronounced on the sample prepared by two-stage deposition due to the initial less dense profile. This study provides an understanding at a molecular level of how surface functionalization alters the structure and howsurface layers respond to changes in calcium ions in the solvent.
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| 6. |
- de Ghellinck, Alexis, et al.
(author)
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Lipid polyunsaturation determines the extent of membrane structural changes induced by Amphotericin B in Pichia pastoris yeast
- 2015
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In: Biochimica et Biophysica Acta - Biomembranes. - : Elsevier BV. - 0005-2736. ; 1848:10, s. 2317-2325
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Journal article (peer-reviewed)abstract
- The activity of the potent but highly toxic antifungal drug Amphotericin B (AmB), used intravenously to treat systemic fungal and parasitic infections, is widely accepted to result from its specific interaction with the fungal sterol ergosterol. While the effect of sterols on AmB activity has been intensely investigated, the role of membrane phospholipid composition has largely been ignored, and structural studies of native membranes have been hampered by their complex and disordered nature. We show for the first time that the structure of fungal membranes derived from Pichia pastoris yeast depends on the degree of lipid polyunsaturation, which has an impact on the structural consequences of AmB activity. AmB inserts in yeast membranes even in the absence of ergosterol, and forms an extra-membraneous layer whose thickness is resolved to be 4-5 nm. In ergosterol-containing membranes, AmB insertion is accompanied by ergosterol extraction into this layer. The AmB-sponge mediated depletion of ergosterol from P. pastoris membranes gives rise to a significant membrane thinning effect that depends on the degree of lipid polyunsaturation. The resulting hydrophobic mismatch is likely to interfere with a much broader range of membrane protein functions than those directly involving ergosterol, and suggests that polyunsaturated lipids could boost the efficiency of AmB. Furthermore, a low degree of lipid polyunsaturation leads to least AmB insertion and may protect host cells against the toxic effects of AmB. These results provide a new framework based on lipid composition and membrane structure through which we can understand its antifungal action and develop better treatments. (C) 2015 Elsevier B.V. All rights reserved.
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| 7. |
- de Ghellinck, Alexis, et al.
(author)
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Production and Analysis of Perdeuterated Lipids from Pichia pastoris Cells
- 2014
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In: PLoS ONE. - : Public Library of Science (PLoS). - 1932-6203. ; 9:4
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Journal article (peer-reviewed)abstract
- Probing molecules using perdeuteration (i.e deuteration in which all hydrogen atoms are replaced by deuterium) is extremely useful in a wide range of biophysical techniques. In the case of lipids, the synthesis of the biologically relevant unsaturated perdeuterated lipids is challenging and not usually pursued. In this work, perdeuterated phospholipids and sterols from the yeast Pichia pastoris grown in deuterated medium are extracted and analyzed as derivatives by gas chromatography and mass spectrometry respectively. When yeast cells are grown in a deuterated environment, the phospholipid homeostasis is maintained but the fatty acid unsaturation level is modified while the ergosterol synthesis is not affected by the deuterated culture medium. Our results confirm that the production of well defined natural unsaturated perdeuterated lipids is possible and gives also new insights about the process of desaturase enzymes.
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| 8. |
- Delhom, Robin, et al.
(author)
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The Antifungal Mechanism of Amphotericin B Elucidated in Ergosterol and Cholesterol-Containing Membranes Using Neutron Reflectometry
- 2020
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In: Nanomaterials. - : MDPI AG. - 2079-4991. ; 10:12
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Journal article (peer-reviewed)abstract
- We have characterized and compared the structures of ergosterol- and cholesterol-containing 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC) membranes before and after interaction with the amphiphilic antifungal drug amphotericin B (AmB) using neutron reflection. AmB inserts into both pure POPC and sterol-containing membranes in the lipid chain region and does not significantly perturb the structure of pure POPC membranes. By selective per-deuteration of the lipids/sterols, we show that AmB extracts ergosterol but not cholesterol from the bilayers and inserts to a much higher degree in the cholesterol-containing membranes. Ergosterol extraction by AmB is accompanied by membrane thinning. Our results provide new insights into the mechanism and antifungal effect of AmB in these simple models of fungal and mammalian membranes and help understand the molecular origin of its selectivity and toxic side effects.
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| 9. |
- Eriksson Skog, Amanda, et al.
(author)
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Interaction of a Histidine-Rich Antimicrobial Saliva Peptide with Model Cell Membranes : The Role of Histidines
- 2023
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In: Langmuir : the ACS journal of surfaces and colloids. - 0743-7463. ; 39:22, s. 7694-7706
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Journal article (peer-reviewed)abstract
- Histatin 5 is a histidine-rich, intrinsically disordered, multifunctional saliva protein known to act as a first line of defense against oral candidiasis caused by Candida albicans. An earlier study showed that, upon interaction with a common model bilayer, a protein cushion spontaneously forms underneath the bilayer. Our hypothesis is that this effect is of electrostatic origin and that the observed behavior is due to proton charge fluctuations of the histidines, promoting attractive electrostatic interactions between the positively charged proteins and the anionic surfaces, with concomitant counterion release. Here we are investigating the role of the histidines in more detail by defining a library of variants of the peptide, where the former have been replaced by the pH-insensitive amino acid glutamine. By using experimental techniques such as circular dichroism, small angle X-ray scattering, quartz crystal microbalance with dissipation monitoring, and neutron reflectometry, it was determined that changing the number of histidines in the peptide sequence did not affect the structure of the peptide dissolved in solution. However, it was shown to affect the penetration depth of the peptide into the bilayer, where all variants except the one with zero histidines were found below the bilayer. A decrease in the number of histidine from the original seven to zero decreases the ability of the peptide to penetrate the bilayer, and the peptide is then also found residing within the bilayer. We hypothesize that this is due to the ability of the histidines to charge titrate, which charges up the peptide, and enables it to penetrate and translocate through the lipid bilayer.
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| 10. |
- Follows, David, et al.
(author)
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Co-adsorption of beta-casein and calcium phosphate nanoclusters (CPN) at hydrophilic and hydrophobic solid-solution interfaces studied by neutron reflectometry
- 2011
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In: Food Hydrocolloids. - : Elsevier BV. - 0268-005X .- 1873-7137. ; 25:4, s. 724-733
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Conference paper (peer-reviewed)abstract
- Neutron reflectometry was used to study the co-adsorption of calcium phosphate nanoclusters (CPN) and beta-casein at hydrophobized and hydrophilic silica-water interfaces. The structural characteristics of the adsorbed layer were determined from neutron reflectivity curves analysed with multi-layer optical models. We used a highly specific proteolytic enzyme, endoproteinase Asp-N in conjunction with a single neutron contrast to verify the model of the protein layer structure. The results showed that the calcium phosphate nanoclusters profoundly affected the rate of adsorption and structure of the interface compared to the adsorption of beta-casein alone and for the hydrophobic interface the effects depended on the point at which the nanoclusters were added. It is proposed that the nanoclusters become surface active because whole beta-casein molecules can replace one or more of the hydrophilic peptides in the shell of the nanoclusters. (C) 2010 Elsevier Ltd. All rights reserved.
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