Effects of lipids and heparin sulphate on formation of amyloid fibril from alpha(s1)-casein

Abstract

αs1-Casein is the major protein in milk and has a molecular chaperone action. With the interest in that, whether κ-and αs2-casein can form amyloid fibrils or not, we investigated amyloid fibril formation from αs1-casein by means of ThT assay, transmission electron microscopy and circular dichroism(CD) spectra. The results show that amyloid fibrils formed from αs1-casein at pH=5.0-5.4 and 65℃ under heating for 144 h. The CD spectra show that the structure of αs1-casein has changed from α-helical to β sheet core, which are the special structure characters of fibrils. Lipids of D6PC promoted amyloid fibril formation from αs1-casein in the concentration of 0.3 and 1 mmol/L. Heparin sulphate did not influence the fibril formation from αs1-casein in the test. It is concluded that although αs1-casein has the effects of molecular chaperon, but it could still form fibrils under harsh conditions. Lipids can influence amyloid fibril formation from αs1-casein, depanding on concentration. It suggests that there is relationship between lipid in membrane and amyloid fibril formation. The results are helpful to exploring the mechanism of fibril formation from αs1-casein.