Browsing by Author "Raynes, JK"

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    Deuterium effects in human serum albumin with nanoparticle silica kinetics
    (Australian Institute of Nuclear Science and Engineering, 2016-11-29) White, JW; Raynes, JK; Mata, JP; Gilbert, EP; Knott, RB; de Campo, L
    Light scattering shows three stages of the interaction of 80Å radius silica nanoparticles with human serum albumin in buffered solutions. The structures formed in the fast stage, twenty minutes after mixing, have been identified in a “stopped flow” neutron small angle scattering experiment. Good scattering functions were obtained at two-minute time resolution for this phase of the interaction in D2O and H2O. pH dependent changes in structure are analysed using standard fitting programs with a minimum number of parameters. This experiment was aimed to find the structural signature of nanoparticle-protein interaction, possibly the “protein corona” supposed to be formed as a means to promote entry of nanoparticles into cells. Here we use small “engineered” nanoparticles where the indications of toxicity are strong. We show with nanometric resolution that for our system, the association is largely a form of protein-induced aggregation distinct from the protein corona hypothesis. The corona might well be the mode of interaction for small proteins and nanoparticles 10-100 times larger than we have studied, but measurements on widely used commercial products may be more relevant.
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    Structure of biomimetic casein micelles: critical tests of the hydrophobic colloid and multivalent-binding models using recombinant deuterated and phosphorylated β-casein
    (SSRN, 2023-10-24) Raynes, JK; Mata, JP; Wilde, KL; Kelly, SM; Holt, C
    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 k-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 b-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. © 2023 The Authors