Amyloid fibril formation by bovine milk kappa-casein and its inhibition by the molecular chaperones alphaS- and beta-casein.
Caseins are a unique and diverse group of proteins present in bovine milk. While their function is presumed to be primarily nutritional, caseins have a remarkable ability to stabilize proteins, i.e., to inhibit protein aggregation and precipitation, that is comparable to molecular chaperones of the small heat-shock protein (sHsp) family. Additionally, sHsps have been shown to inhibit the formation of amyloid fibrils. This study investigated (i) the fibril-forming propensities of casein proteins and their mixture, sodium caseinate, and (ii) the ability of caseins to prevent in vitro fibril formation by kappa-casein. Transmission electron microscopy (TEM) and X-ray fiber diffraction data demonstrated that kappa-casein readily forms amyloid fibrils at 37 degrees C particularly following reduction of its disulfide bonds. The time-dependent increase in thioflavin T fluorescence observed for reduced and nonreduced kappa-casein at 37 degrees C was suppressed by stoichiometric amounts of alphaS- and beta-casein and by the hydrophobic dye 8-anilino-1-naphthalene sulfonate; the inhibition of kappa-casein fibril formation under these conditions was verified by TEM. Our findings suggest that alphaS- and beta-casein are potent inhibitors of kappa-casein fibril formation and may prevent large-scale fibril formation in vivo. Casein proteins may therefore play a preventative role in the development of corpora amylacea, a disorder associated with the accumulation of amyloid deposits in mammary tissue.
Thorn
David C
DC
School of Chemistry and Physics, The University of Adelaide, Adelaide, South Australia 5005, Australia.
Meehan
Sarah
S
Sunde
Margaret
M
Rekas
Agata
A
Gras
Sally L
SL
MacPhee
Cait E
CE
Dobson
Christopher M
CM
Wilson
Mark R
MR
Carver
John A
JA
D000682:Amyloid / Q000138:chemical synthesis* / Q000737:chemistry / Q000648:ultrastructure; D000817:Anilino Naphthalenesulfonates / Q000737:chemistry; D000818:Animals; D052160:Benzothiazoles; D002364:Caseins / Q000737:chemistry*; D002417:Cattle; D004229:Dithiothreitol / Q000737:chemistry; D008623:Mercaptoethanol / Q000737:chemistry; D046529:Microscopy, Electron, Transmission; D008894:Milk Proteins / Q000737:chemistry; D008956:Models, Chemical; D018832:Molecular Chaperones / Q000737:chemistry*; D010084:Oxidation-Reduction; D012710:Serum Albumin, Bovine / Q000737:chemistry; D013050:Spectrometry, Fluorescence; D013696:Temperature; D013844:Thiazoles / Q000737:chemistry; D014961:X-Ray Diffraction
D000682:Amyloid; D000817:Anilino Naphthalenesulfonates; D052160:Benzothiazoles; D002364:Caseins; D008894:Milk Proteins; D018832:Molecular Chaperones; D013844:Thiazoles; C009462:thioflavin T; D012710:Serum Albumin, Bovine; D008623:Mercaptoethanol; C027132:1-anilino-8-naphthalenesulfonate; D004229:Dithiothreitol