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Type: Journal article
Title: Amyloid fibril formation by bovine milk αs₂-casein occurs under physiological conditions yet is prevented by its natural counterpart, αs₁-casein
Other Titles: Amyloid fibril formation by bovine milk alpha (s2)-casein occurs under physiological conditions yet is prevented by its natural counterpart, alpha (s1)-casein
Author: Thorn, D.
Ecroyd, H.
Sunde, M.
Poon, S.
Carver, J.
Citation: Biochemistry, 2008; 47(12):3926-3936
Publisher: Amer Chemical Soc
Issue Date: 2008
ISSN: 0006-2960
Statement of
Thorn David C., Ecroyd Heath, Sunde Margaret, Poon Stephen and Carver John A.
Abstract: The calcified proteinaceous deposits, or corpora amylacea, of bovine mammary tissue often comprise a network of amyloid fibrils, the origins of which have not been fully elucidated. Here, we demonstrate by transmission electron microscopy, dye binding assays, and X-ray fiber diffraction that bovine milk alpha s2-casein, a protein synthesized and secreted by mammary epithelial cells, readily forms fibrils in vitro. As a component of whole alpha s-casein, alpha s2-casein was separated from alpha s1-casein under nonreducing conditions via cation-exchange chromatography. Upon incubation at neutral pH and 37 degrees C, the spherical particles typical of alpha s2-casein rapidly converted to twisted, ribbon-like fibrils approximately 12 nm in diameter, which occasionally formed loop structures. Despite their irregular morphology, these fibrils possessed a beta-sheet core structure and the ability to bind amyloidophilic dyes such as thioflavin T. Fibril formation was optimal at pH 6.5-6.7 and was promoted by higher incubation temperatures. Interestingly, the protein appeared to be less prone to fibril formation upon disulfide bond reduction with dithiothreitol. Thus, alpha s2-casein is particularly susceptible to fibril formation under physiological conditions. However, our findings indicate that alpha s2-casein fibril formation is potently inhibited by its natural counterpart, alpha s1-casein, while is only partially inhibited by beta-casein. These findings highlight the inherent propensity of casein proteins to form amyloid fibrils and the importance of casein-casein interactions in preventing such fibril formation in vivo.
Keywords: Animals
Microscopy, Electron, Transmission
Chromatography, Ion Exchange
X-Ray Diffraction
Circular Dichroism
Ultraviolet Rays
Hydrogen-Ion Concentration
Description: Copyright © 2008 American Chemical Society
DOI: 10.1021/bi701278c
Appears in Collections:Aurora harvest 6
Chemistry publications

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