Assembly of iron-bound ovotransferrin amyloid fibrils

The impacts of pH, temperature, ionic strength and stirring speed on the assembly of ovotransferrin (OVT) into amyloid fibrils were analyzed by using thioflavin T fluorescence and atomic force microscopy. Optimum OVT nanofibrillation condition was achieved at pH 2, 90 °C, an ionic strength of 150 mM and a stirring speed of 300 rpm. Apart from rigid and long amyloid fibrils, flexible and short amyloid fibrils were also detected under the optimal condition. Morphological changes observed by atomic force microscopy as a function of time demonstrated that short OVT amyloid fibrils (with contour length below 800 nm) were generated upon heating for 1 h, and long OVT amyloid fibrils (with contour length above 800 nm) appeared after 6 h heating. In terms of structural characteristics, circular dichroism study revealed that internal structures of OVT amyloid fibrils could be stacked β-sheet. Analysis of fibril periodicity indicated that OVT amyloid fibrils might consist of 2 or 4 multi-stranded filaments. With the aid of ANS (1-anilino-8-naphthalensulfonate) fluorescence probe, it was found that OVT amyloid fibrils had lower surface hydrophobicity than untreated OVT. MTT (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide) assay showed that OVT amyloid fibrils had no in vitro cytotoxicity, implying great application potential in food. This work will advance our understanding of amyloid fibrils derived from iron-bound proteins.