Browsing by Author "McGillivray, DJ"

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    The assembly mechanism and mesoscale architecture of protein–polysaccharide complexes formed at the solid–liquid Interface
    (American Chemical Society, 2022-10-04) Biswas, S; Melton, LD; Nelson, ARJ; Le Brun, AP; Heinrich, F; McGillivray, DJ; Xu, AY
    Protein-polysaccharide composite materials have generated much interest due to their potential use in medical science and biotechnology. A comprehensive understanding of the assembly mechanism and the mesoscale architecture is needed for fabricating protein-polysaccharide composite materials with desired properties. In this study, complex assemblies were built on silica surfaces through a layer-by-layer (LbL) approach using bovine beta-lactoglobulin variant A (βLgA) and pectin as model protein and polysaccharide, respectively. We demonstrated the combined use of quartz crystal microbalance with dissipation monitoring (QCM-D) and neutron reflectometry (NR) for elucidating the assembly mechanism as well as the internal architecture of the protein-polysaccharide complexes formed at the solid-liquid interface. Our results show that βLgA and pectin interacted with each other and formed a cohesive matrix structure at the interface consisting of intertwined pectin chains that were cross-linked by βLgA-rich domains. Although the complexes were fabricated in an LbL fashion, the complexes appeared to be relatively homogeneous with βLgA and pectin molecules spatially distributed within the matrix structure. Our results also demonstrate that the density of βLgA-pectin complex assemblies increased with both the overall and local charge density of pectin molecules. Therefore, the physical properties of the protein-polysaccharide matrix structure, including density and level of hydration, can be tuned by using polysaccharides with varying charge patterns, thus promoting the development of composite materials with desired properties. © 2024 American Chemical Society
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    Combined pressure and temperature denaturation of ribonuclease A produces alternate denatured states
    (Elsevier, 2016-05-13) Ryan, TM; Xun, Y; Cowieson, NP; Mata, JP; Jackson, AJ; Pauw, BR; Smith, AJ; Kirby, N; McGillivray, DJ
    Protein folding, unfolding and misfolding have become critically important to a range of health and industry applications. Increasing high temperature and high pressure are used to control and speed up reactions. A number of studies have indicated that these parameters can have a large effect on protein structure and function. Here we describe the additive effects of these parameters on the small angle scattering behaviour of ribonuclease A. We find that alternate unfolded structures can be obtained with combined high pressure and temperature treatment of the protein. © 2016 Elsevier Inc.
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    Formation of hydrated layers in PMMA thin films in aqueous solution
    (Elsevier, 2015-10-30) Akers, PW; Nelson, A; Williams, DE; McGillivray, DJ
    Neutron reflectometry (NR) measurements have been made on thin (70–150 Å) poly(methylmethacrylate) (PMMA) films on Si/SiOx substrates in aqueous conditions, and compared with parameters measured using ellipsometry and X-Ray reflectometry (XRR) on dry films. All techniques show that the thin films prepared using spin-coating techniques were uniform and had low roughness at both the silicon and subphase interfaces, and similar surface energetics to thicker PMMA films. In aqueous solution, NR measurements at 25 °C showed that PMMA forms a partially hydrated layer at the SiOx interface 10 Å under the film, while the bulk film remains intact and contains around 4% water. Both the PMMA film layer and the sublayer showed minimal swelling over a period of 24 h. At 50 °C, PMMA films in aqueous solution roughen and swell, without loss of PMMA material at the surface. After cooling back to 25 °C, swelling and roughening increases further, with loss of material from the PMMA layer. © 2017 Elsevier B.V.
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    Investigating biomimetic calcium phosphate and carbonate mineral formation within multilayered biopolymer films using small angle neutron scattering
    (International Conference on Neutron Scattering, 2017-07-12) Shahlori, R; Nelson, A; Mata, JP; Waterhouse, GIN; McGillivray, DJ
    We have produced a multilayered template using chitosan and iota-carrageenan as a substrate for mineralised calcium phosphate or calcium carbonate through exposure to a simulated body fluid (SBF) or simulated sea-water (SSW), respectively. A film consisting of 120-bilayers of these alternating charged biopolymers was successfully dip-coated onto microscope slides and mineralised. The films produced showed striking iridescence due to the periodically alternating nanoscale structure, a golden sheen was observed when the unmineralised film was swollen and transitioned to a blue colour upon mineralisation. Cryo-SEM and TEM images showed the nanoscale structure responsible for the observed iridescence can be attributed to the dense interfaces between the chitosan and iota-carrageenan bilayers. Small angle neutron scattering measurements were conducted using QUOKKA at the Australian Nuclear Science and Technology Organisation (ANSTO). These measurements revealed a scattering feature, between 0.002-0.006 A-1, exclusively for mineralised samples. The large structure (150 nm) responsible for this feature was modelled as lamellar objects attributed to the interfaces between the chitosan and iota-carrageenan layers. This feature becomes more prominent as the nSLD contrast against D2O increases with more mineralised samples. The power law slope of low-q scattering is also shown to increase from 2.2 to 3.8, from an unmineralised to the most mineralised film. This result shows that increase is the overall smoothness and rigidity of the biopolymer film is achieved with mineralisation. A high-q scattering features was observed between 0.01-0.05 A-1, arising from spacing between the polymer mesh within the swollen multilayered film. However, this feature was shown to have no significant changes upon mineralisation. These parameters were compared with films mineralised with different heavy metal ion treatments (Cu2+, Zn2+, Pb2+ and Cd2+) to observe the effect on mineral nucleation, which is of concern for shell-fish growth near industrial areas. Additionally the effect of acidic molecules (L-Glutamic acid, Citric acid and poly-acrylic acid) was also measured, to access the mineralisation influence of calcium ion adsorption on carboxylic acid groups.
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    Mechanistic understanding of PHD2 enzyme upon ligand interactions using SAXS and SANS
    (International Conference on Neutron Scattering, 2017-07-12) Vadakkedath, PG; Ryan, TM; Leung, IKH; McGillivray, DJ
    Prolyl hydroxylase domain proteins (PHDs) play an important role in the regulation of cellular homeostasis in response to changes in cellular oxygen level.1 In the presence of oxygen, PHDs catalyse the oxygen-dependent hydroxylation of hypoxia inducible factor (HIF), which lead to its degradation. However, in the absence of oxygen, HIF cannot be hydroxylated and can therefore trigger downstream hypoxic responses including the formation of new blood vessels and red bloodcells. PHDs catalyse the hydroxylation of HIF at two different proline residues.2–3 We are interested in understanding the structural basis in the substrate selectivity of PHDs. Using small angle X-ray scattering (SAXS), we examined the conformational changes of PHD2 particularly ?2 ?3 loop in the presence of CODD and NODD substrates where we see change in overall size and shape of PHD2. We obtained PHD2-NODDsolution structure as a confirmation to crystallographic structure3. We would further confirm these conformational changes upon ligand interactions using Small angle neutron scattering. It would help us in understand ?2 ?3 loopand ?4 regions of PHD2 which is crucial in binding of CODD and NODD substrates. The contribution of ?2 ?3 loop and ?4 regions of PHD2 in protecting the active site is known from the NMR data2–3. Both SAXS and SANS would be complementary to NMR data in solution which would further help us in design PHD2 inhibitors for hypoxia related diseases like ischemic heart disease and anaemia.
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    Nano- and microstructure of high-internal phase emulsions under shear
    (American Chemical Society, 2010-03-18) Yaron, PN; Reynolds, PA; McGillivray, DJ; Mata, JP; White, JW
    High-internal phase aqueous-in-oil emulsions of two surfactant concentrations were studied using small-angle neutron scattering (SANS) and simultaneous in situ rheology measurements. They contained a continuous oil phase with differing amounts of hexadecane and d-hexadecane (for contrast matching experiments), a deuteroaqueous phase almost saturated with ammonium nitrate, and an oil-soluble stabilizing polyisobutylene-based surfactant. The emulsions’ macroscopic rheological behavior has been related to quantify changes in microscale and nanoscale structures observed in the SANS measurements. The emulsions are rheologically unexceptional and show, inter alia, refinement to higher viscosity after high shear, and shear thinning. These are explained by changes observed in the SANS model parameters. Shear thinning is explained by SANS-observed shear disruption of interdroplet bilayer links, causing deflocculation to more spherical, less linked, aqueous droplets. Refinement to higher viscosity is accompanied by droplet size reduction and loss of surfactant from the oil continuous phase. Refinement occurs because of shear-induced droplet anisotropy, which we have also observed in the SANS experiment. This observed anisotropy and the emulsion refinement cannot be reproduced by either isolated molecule or mean-field models but require a more detailed consideration of interdroplet forces in the sheared fluid. © 2010, American Chemical Society
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    Nanoplastics – protein interaction: a scattering study of transition from soft and hard corona
    (Australian Institute of Nuclear Science and Engineering (AINSE), 2018-11-19) Kihara, S; Koeper, I; Seal, C; McGillivray, DJ; Mata, JP
    There is growing concern about plastic waste in the environment, and its impact on biological organisms. While bulk plastics are thought to be non-toxic, when the plastics break down to a sub-micron length scale (i.e. nanoplastics), they obtain extra mobility inside living things, and may cause various adverse effects [1,2]. This, coupled with a lack of knowledge surrounding the dangers from different types of plastics, prevents well-designed responses to the problem. Hypothetically, the potential adverse effects are caused by protein denaturation, oxidative stress and/or cellular mem brane damage. However, the inherent complexity of biological systems makes it challenging to gain a mechanistic understanding. Adding complexity to this problem, the potential adverse effects are highly dependent on the nature of nanoparticles (NPs) – the contributing factors could include elemental composition, chemistry of the plastic surface, and/or size of the plastic particle [3,2,4]. When in biological systems, nanoplastics are surrounded by various types of proteins5. The structure of proteins surrounding nanoplastics are important parameters to understand the interaction of nanoplastic/protein composite. We carried out light scattering and small angle neutron scattering (SANS) experiments to explore the structure of the protein corona on monodisperse polystyrene spheres using a model protein human serum albumin (HSA). The geometry of the PS/HSA complex was investigated with a contrast matching method. The transition from a “soft” to a “hard” interaction between the nanoparticle and the protein was observed when pH is lowered from 7.4, and the implications of this on nanoplastic toxicity is discussed. © The Authors.
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    A neutron reflectivity study of the interfacial and thermal behaviour of surface-attached hairpin DNA
    (Royal Society of Chemistry, 2011-01-01) Kjallman, THM; Nelson, A; James, M; Dura, JA; Travas-Sejdic, J; McGillivray, DJ
    Mixed self-assembled monolayers (mSAMs) have been successfully utilised as platforms for gene sensors, employing optical as well as electrochemical means of detection. Probe density is one of the most important parameters in the construction of such a sensor and thus a fundamental understanding of the structure within the mSAM is vital. In this work, the interfacial behaviour of mixed SAMs, where short PEG oligomers co-adsorbed to the surface with hairpin structured oligonucleotide (ODN) probes, has been investigated. The neutron reflectivity of the mixed SAMs was measured at differing HPP : PEG ratios, and through two routes of formation, to elucidate the effect of controlled HPP surface density on surface conformation of the probes and on the final hybridised ODN-HPP construct. General conclusions regarding the structure of the investigated SAMs could be drawn from determined thickness and volume fraction values and conformational changes in the mSAM, induced by hybridisation with complementary ODN, were also detected. An investigation of the melting behaviour of the surface-attached HPPs was also conducted with polarised neutron reflectivity and clear signs of melting were observed in the reflectivity and the SLD profiles around 45 [degree]C.© 2011, Royal Society of Chemistry
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    Proceedings of the 15th International Small-Angle Scattering Conference (SAS2012)
    (2013-02-19) McGillivray, DJ; Trewhella, J; Gilbert, EP; Hanley, TL
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    Stability of high internal phase emulsions at low surfactant concentration studied by small angle neutron scattering
    (Elsevier, 2010-09-15) Reynolds, PA; McGillivray, DJ; Mata, JP; Yaron, PN; White, JW
    The changes in structure of high internal phase emulsions at low concentrations and at elevated temperature are reported for comparison with the same emulsions under conditions well away from instability. Small angle neutron scattering measurements on aqueous ammonium nitrate droplets dispersed in hexadecane and stabilized by very small quantities of a polyisobutylene-based surfactant (PIBSA) as well as related inverse micellar solutions in hexadecane, have been made as a function of temperature and surfactant concentration. Experimental conditions here favour larger and more deformable droplets than in previous studies. Besides the expected micelles and adsorbed surfactant, planar bilayers of micron lateral extent between touching droplets cover 20% of the droplet surface. Another difference from previous experiments is that the oil phase in the emulsions, and corresponding inverse micellar solutions are different in micellar radii and composition. The differences, and changes with surfactant concentration and temperature, are attributed to fractionation of the polydisperse PIBSA in the emulsions, but not the inverse micellar solutions. At low PIBSA concentration and high temperature the SANS shows emulsion decomposing into separate oil and aqueous phases. This occurs when the micelle concentration reaches a very small but measurable value. The inverse micelles may suppress by steric action long wavelength unstable capillary waves in the bilayers. Depletion repulsion forces here have a minor role in the emulsion stabilization. © 2010, Elsevier Ltd.
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    Sugar-coated proteins: the importance of degree of polymerisation of oligo-galacturonic acid on protein binding and aggregation
    (Royal Society of Chemistry, 2017-03-14) Xu, AY; Melton, LD; Ryan, TM; Mata, JP; Jameson, GB; Rekas, A; Williams, MAK; McGillivray, DJ
    We have simplified the structural heterogeneity of protein–polysaccharide binding by investigating protein binding to oligosaccharides. The interactions between bovine beta-lactoglobulin A (βLgA) and oligo-galacturonic acids (OGAs) with various numbers of sugar residues have been investigated with a range of biophysical techniques. We show that the βLgA–OGA interaction is critically dependent on the length of the oligosaccharide. Isothermal titration calorimetry results suggest that a minimum length of 7 or 8 sugar residues is required in order to exhibit appreciable exothermic interactions with βLgA – shorter oligosaccharides show no enthalpic interactions at any concentration ratio. When titrating βLgA into OGAs with more than 7–8 sugar residues the sample solution also became turbid with increasing amounts of βLgA, indicating the formation of macroscopic assemblies. Circular dichroism, thioflavin T fluorescence and small angle X-ray/neutron scattering experiments revealed two structural regimes during the titration. When OGAs were in excess, βLgA formed discrete assemblies upon OGA binding, and no subsequent aggregation was observed. However, when βLgA was present in excess, multi-scale structures were formed and this eventually led to the separation of the solution into two liquid-phases. © 2017 The Royal Society of Chemistry