Fibrillation of egg white ovalbumin: a pathway via biomineralization

Here we report the fibrillation of egg white ovalbumin (OVA) induced by the biomineralization of two alkali halides (KCl, NaCl) in the Langmuir-Blodgett (LB) film of OVA. The pressure-area isotherm of OVA shows the salt-induced increment of apparent area/monomer of OVA. Fibrillation of OVA in the LB film is monitored by FE-SEM imaging. Formation of fibrillar aggregates is concomitant with an increase of salt concentration. HR-TEM and EDX measurements allowed us to identify nanostructured crystals of salt, which are associated with this fibrillar structure. FTIR spectroscopic study of the amide band in LB films as well as CD spectroscopy in solution qualitatively indicates the increase in β-sheet to α-helix ratio in the presence of salt, indicating unfolding of protein. We suggest that the ion attachment to the peptide chain leads to unfolding and that subsequent recrystallization in the transferred monolayer leads to fibrillation of protein as well as biomineralization of alkali halide salts. This finding demonstrates that the fibrillation of OVA is induced by the biomineralization of alkali halides.