Amyloid fibril formation by β-Casein and its influence factor

Abstract

beta-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 to beta-casein fibril formation. In order to study the time course of fibril formation by beta-casein, the samples were incubated and picked up at specific times and tested by ThT assay and transmission electron microscopy. The results showed that amyloid fibrils were not formed by beta-casein incubated in pH=5.4-9.0 at 65 degrees C for 252 h, which suggested that beta-casein is a good molecular chaperone. The beta-casein fibril formation was promoted in the presence of longer-chain phosphatidylcholine lipids(D6PC and D9PC), which indicated that the interaction of beta-casein with biomembrane of mammary gland abundant with lipids maybe caused beta-casein structure changed from native to more beta-sheet. Heparin sulphate, a major component of the extracellular matrix and a species which is commonly associated with extracellular amyloid deposits, interacted with beta-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.