Influence of metal ions on thermal aggregation of bovine serum albumin:Aggregation kinetics and structural changes

Metal ions are implicated in protein aggregation processes of several neurodegenerative pathologies. Inthis work the effects of Cu(II) and Zn(II) ions on heat-induced structural modifications of bovine serumalbumin (BSA) were studied, with the aim of delineating the role of these ions in the early stages of proteinsaggregation kinetics. A joint application of different techniques was used. The aggregate growth wasfollowed by dynamic light scattering measurements, whereas the conformational changes occurring inthe protein structure were monitored by Raman and IR spectroscopy. Both in absence and in presenceof metal ions, heating treatment gave rise to b-structures to the detriment of a-helix conformation ofBSA. The temperature of protein unfolding was not sensitively affected by the presence of Zn(II) or Cu(II)ions; on the contrary, only Zn(II) ions slightly promoted the heat-induced aggregation of the protein,since bigger aggregates were formed in their presence. The different efficacy of the Cu(II) and Zn(II) ionsin promoting the BSA aggregation were highlighted by Raman measurements, assessing the role of Hisresidues in metal binding. A distinct polypeptide folding of the two metal–BSA systems takes place, sincethe predominant mode of metal binding depends on metal. In particular, in Zn–BSA the metal coordinationinvolves the imidazole Ns atom of His which can promote inter-molecular cross-linking.2009 Elsevier Inc. All rights reserved.