Effects of a flow field on amyloid fibrillogenesis in a β-lactoglobulin solution

• Effect of stirring was studied on the fibril formation of β-lactoglobulin.
• Elongational-flow birefringence (Taylor's Four-Roller Mill) method was used to characterize the fibrillogenesis of β-lactoglobulin.
• Rotational diffusion coefficient (Dr), a quantitative study was determined to study the growth of the fibrils.
• Fibrillogenesis of β-lactoglobulin was enhanced on increasing stirring rate but fibrils fragmented over high stirring rate.

The effects of a flow field on the amyloid fibrillogenesis of β-lactoglobulin (βLG) were investigated using a flow birefringence method and AFM imaging experiments. A 4 wt% βLG aqueous solution was incubated at pH 2 and 80 °C. A flow field was then applied by stirring at 250 and 474 rpm. An incubation without stirring was used as a control sample. Flow birefringence measurements were taken at room temperature from the incubated sample solutions in which an elongational flow field was used. The birefringence pattern obtained indicated that the fibrils formed by the incubation were rigid rod-like molecules. Birefringence relaxation experiments revealed at least two relaxation processes, suggesting a double peaked distribution function for fibrils length. The length distribution of fibrils expected from the birefringence experiments was confirmed by the AFM images of amyloid fibrils. The order of the expected length of the resultant fibrils in both longer and shorter length distributions was those stirred at 250 rpm ≅ 474 rpm > 0 rpm. The effects of the flow field applied during the incubation on amyloid fibrillogenesis was discussed on the basis of the rate process consideration. The present results demonstrated that the flow field should be considered as an important factor that regulates the fibrillogenesis of globular proteins.

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