Formation of rice protein fibrils is highly sensitive to the different types of metal ions: Aggregation behavior and possible mechanisms

Abstract

The effects of Ca²⁺, Cu²⁺, and Fe³⁺ on rice protein (RP) fibril formation were investigated in this study. Low Ca²⁺ concentration (≤150 mM) moderately unfolded the conformation of RP, promoting the exposure of hydrophobic sites and RP fibril assembly. Fibril formation was especially promoted with earlier addition of Ca²⁺. Cu²⁺ and Fe³⁺ inhibited RP fibril formation in a dose-dependent manner, and the inhibitory effect of Fe³⁺ was stronger due to higher affinity with RP. Additionally, the addition of Cu²⁺ and Fe³⁺ reduced α-helix and β-sheet contents of RP, respectively, hindering the formation of stacked β-sheet, the main internal structure of fibrils. These two ions also resulted in the formation of random aggregates within 15-50 nm, which further inhibited the conversion of proteins to fibrils. Moreover, Cu²⁺ and Fe³⁺ prevented the recruitment of nucleus into fibril-growth-sites, and formed fibrils were disrupted into fragments when these ions were added.

Keywords: Fibril; Improve; Inhibit; Ions; Rice protein.