β-酪蛋白淀粉样纤维沉淀的形成及影响因素

Amyloid Fibril Formation by β-Casein and Its Influence Factor

利用硫磺素T（ ThT）荧光分析法和透射电子显微镜检测β-酪蛋白形成淀粉样纤维沉淀（ Fibril）的动力学过程,研究了磷脂和硫酸肝素对其 Fibril 形成的影响.实验结果表明,β-酪蛋白在65℃下, pH 值为5.4~9.0的范围内,加热252 h以上,并未形成Fibril,说明β-酪蛋白是一种很好的分子伴侣,在高温、弱酸和弱碱条件下均不形成淀粉样纤维沉淀.甘油磷酸胆碱D6PC和D9PC可以显著地促进β-酪蛋白的Fibril的形成,说明一定条件下蛋白质可能与细胞膜之间存在相互作用而导致其二级构象的转变.硫酸肝素对β-酪蛋白形成Fibril具有促进作用,在炎症组织中,硫酸肝素表达量的增加有可能促进β-酪蛋白形成Fibril,说明乳腺炎与乳腺中的Corpora Amylacea的形成存在一定的联系.

β-Casein is the second abundant among the casein proteins in bovine milk and reported to exhibite biological activities. In this study, the focus was placed on the influence of lipids and heparin sulphate toβ-casein fibril formation. In order to study the time course of fibril formation byβ-casein, the samples were in-cubated and picked up at specific times and tested by ThT assay and transmission electron microscopy. The re-sults showed that amyloid fibrils were not formed byβ-casein incubated in pH=5. 4—9. 0 at 65 ℃ for 252 h, which suggested that β-casein is a good molecular chaperone. The β-casein fibril formation was promoted in the presence of longer-chain phosphatidylcholine lipids（D6PC and D9PC）, which indicated that the interac-tion of β-casein with biomembrane of mammary gland abundant with lipids maybe caused β-casein structure changed from native to more β-sheet. Heparin sulphate, a major component of the extracellular matrix and a species which is commonly associated with extracellular amyloid deposits, interacted with β-casein to promote its aggregation. It is supposed that Corpora Amylacea is associated with mastitis because of high expression of heparin sulphate in inflamed mammary. This study explored that it is possible for chaperon proteins to form amyloid fibrils influenced by components in vivo and lose its chaperon effects.