Chemical and physical characterization of thermal aggregation of model proteins modulated by zinc(II) and copper(II) ions

BACKGROUND: Metal ions are implicated in protein aggregation processes of several neurodegenerative pathologies, where the protein deposition occurs, and in the biotechnology field like the food technology where many processes in food manufacturing are based on thermal treatments. OBJECTIVE: The influence of Cu2+ or Zn2+ ions on the thermal aggregation process of Bovine beta-lactoglobulin (BLG) and Bovine Serum Albumin (BSA), two protein models, was studied with the aim of delineating the role of these ions in the protein aggregation kinetics and to clarify the related molecular mechanisms. METHODS: The protein structure changes were monitored by Raman spectroscopy, whereas the aggregate growth was followed by Dynamic Light Scattering measurements. RESULTS: Both metal ions are able to favour the BLG aggregation, whereas only Zn2+ ions have a promoter effect on the thermal aggregation of BSA. The reason of this different behaviour is that the BLG aggregation evolution is manly affected by the redistribution of charges, whereas that of BSA by the metal coordination binding which depends on metal. CONCLUSIONS: Raman spectroscopy, combined with dynamic light scattering experiments, was very useful in identifying the role played by Cu2+ and Zn2+ on the aggregation pathways of BLG and BSA. The results provide evidence for the role of histidine residues both in the redistribution of charges and in the two modes of metal binding that take place in BLG- and BSA-containing systems, respectively.