Influence of cadmium ion on denaturation kinetics of hen egg white-lysozyme under thermal and acidic conditions.

To study the influence of Cd(II) ions on denaturation kinetics of hen egg white lysozyme (HEWL) under thermal and acidic conditions, spontaneous Raman spectroscopy in conjunction with Thioflavin-T fluorescence, AFM imaging, far-UV circular dichroism spectroscopy, and transmittance assays was conducted. Four distinctive Raman spectral markers for protein tertiary and secondary structures were recorded to follow the kinetics of conformational transformation. Through comparing variations of these markers in the presence or absence of Cd(II) ions, Cd(II) ions show an ability to efficiently accelerate the disruption of tertiary structure, and meanwhile, to promote the direct formation of organized β-sheets from the uncoiling of α-helices by skipping intermediate random coils. More significantly, with the action of Cd(II) ions, the initially resulting oligomers with disordered structures tend to assemble into aggregates with random structures like gels more than amyloid fibrils, along with a so-called "off-pathway" denaturation pathway. Our results advance the in-depth understanding of corresponding ion-specific effects.