Supramolecular structure of the casein micelle
Supramolecular structure of the casein micelle
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DOI：
10.3168/jds.2007-0819
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发表时间：
2008-05-01
影响因子：
3.5
通讯作者：
Oommen, B. S.
中科院分区：
文献类型：
--
作者：
McMahon, D. J.;Oommen, B. S.
牛奶中的胶体酪蛋白胶束的超分子结构进行了研究，通过使用的样品制备协议的基础上吸附的蛋白质上的聚-L-赖氨酸和parlodion涂层铜网格，染色的蛋白质和磷酸钙的草酸铀酰，瞬时冷冻，并在高真空下干燥。高分辨率透射电子显微镜立体图像显示酪蛋白胶束的内部结构。在我们对这些图像的解释的基础上，开发了一种互锁晶格模型，其中酪蛋白-磷酸钙聚集体和酪蛋白聚合物链共同作用以保持酪蛋白胶束的完整性。酪蛋白形成由酪蛋白稳定的磷酸钙纳米簇互锁的线性和支链（2至5个蛋白质长）。该模型表明，通过α（s1）-、α（s2）-或β-酪蛋白或其组合的磷酸丝氨酸结构域稳定磷酸钙纳米簇，将使其疏水结构域向外定向，从而允许与其他酪蛋白分子相互作用和结合。酪蛋白之间的其他相互作用，如钙桥，也可能发生，并进一步稳定超分子。具有互锁晶格结构和多重相互作用的组合导致开放的海绵状胶体超分子，其抵抗空间变化和崩解。当磷酸钙纳米簇溶解时，围绕磷酸钙纳米簇的酪蛋白之间的疏水相互作用将防止酪蛋白胶束的完全解离。同样地，酪蛋白之间的钙桥接和其他静电相互作用将防止酪蛋白胶束在牛奶冷却或将尿素添加到牛奶中时解离成酪蛋白-磷酸钙纳米簇聚集体，并且疏水相互作用降低。牛奶合成过程中的聚合物链和小聚集体颗粒的外观也将基于酪蛋白胶束的这种互锁晶格模型，并且其超分子结构因此表现出自然界中观察到的自聚集、相互依赖和多样性的原理。
The supramolecular structure of colloidal casein micelles in milk was investigated by using a sample preparation protocol based on adsorption of proteins onto a poly-L-lysine and parlodion-coated copper grid, staining of proteins and calcium phosphate by uranyl oxalate, instantaneous freezing, and drying under a high vacuum. High-resolution transmission electron microscopy stereo-images were obtained showing the interior structure of casein micelles. On the basis of our interpretation of these images, an interlocked lattice model was developed in which both casein-calcium phosphate aggregates and casein polymer chains act together to maintain casein micelle integrity. The caseins form linear and branched chains ( 2 to 5 proteins long) interlocked by the casein-stabilized calcium phosphate nanoclusters. This model suggests that stabilization of calcium phosphate nanoclusters by phosphoserine domains of alpha(s1)-, alpha(s2)-, or beta-casein, or their combination, would orient their hydrophobic domains outward, allowing interaction and binding to other casein molecules. Other interactions between the caseins, such as calcium bridging, could also occur and further stabilize the supramolecule. The combination of having an interlocked lattice structure and multiple interactions results in an open, sponge-like colloidal supramolecule that is resistant to spatial changes and disintegration. Hydrophobic interactions between caseins surrounding a calcium phosphate nanocluster would prevent complete dissociation of casein micelles when the calcium phosphate nanoclusters are solubilized. Likewise, calcium bridging and other electrostatic interactions between caseins would prevent dissociation of the casein micelles into casein-calcium phosphate nanocluster aggregates when milk is cooled or urea is added to milk, and hydrophobic interactions are reduced. The appearance of both polymer chains and small aggregate particles during milk synthesis would also be expected based on this interlocked lattice model of casein micelles, and its supramolecule structure thus exhibits the principles of self-aggregation, interdependence, and diversity observed in nature.