Browsing by Author "Kelly, SM"

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    Silica condensation by a silicatein α homologue involves surface-induced transition to a stable structural intermediate forming a saturated monolayer
    (American Chemical Society, 2010-09-29) Patwardhan, SV; Holt, SA; Kelly, SM; Kreiner, M; Perry, CC; van der Walle, CF
    Silicatein alpha exists within the protein filament of silica spicules of the marine sponge Tethya aurantium in a predominantly beta-sheet structure. However, it is produced in a soluble form with mixed alpha-helix/beta-sheet structure akin to its cathepsin L homologue. To understand this conformational transition in the context of enzyme catalyzed silica condensation, we used a functional, recombinant silicatein alpha termed 4SER. In solution, 4SER becomes conformationally unstable at pH 7 and readily unfolds to a soluble beta-sheet intermediate, losing the majority of its helical structure. This beta-sheet intermediate is present following adsorption of 4SER to a silica surface from solution. 4SER is particularly surface active, forming a near saturated monolayer on SiO(2) from low bulk concentrations, without transition to multilayers at high bulk concentrations. The adsorbed intermediate remains stable during silica condensation and drying. We propose that the beta-sheet structure for silicatein a. in marine sponge spicules represents a stable structural intermediate, formed upon adsorption to the silica surface. Copyright © 2010 American Chemical Society
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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