Molecular basis of the role played by Cu2+ and Zn2+ ions during the thermal aggregation processes of beta-lactoglobulin (BLG) were studied by using a joint application of different techniques [1]. In particular, Raman spectroscopy was very useful in identifying the different effects caused by the two metals at molecular level (i.e. changes in His protonation state, disulfides bridge conformation, and micro-environment of aromatic residues), evidencing the primary importance of the protein charge distribution during the aggregation process. In particular, changes in His protonation were revealed by the curve fitting analysis of the 1080-920 cm-1 Raman region (Figure 1). In the native BLG the two His residues are in the tautomeric I form (100%), as indicated by the presence of the marker band at ?990 cm-1. After the thermal treatment, also the cationic form of His (His+) gave a small contribution, as suggested by a new component visible at 995 cm-1. A similar trend was obtained in the presence of both Zn2+ and Cu2+ ions, although the contribution of the component due to the His+ form (at ?996 cm-1) was more relevant in the presence of Zn2+ ions (about 30 %). Both metal ions are able to act on protein charge distribution and favour the protein aggregation, but Zn2+ is able to alter the natural conformational state of BLG, causing a slight unfolding. The latter, in addition to a more relevant redistribution of charges induced by Zn2+, gives rise to a different screening of electrostatic interactions between charged BLG molecules, favouring the formation of bigger aggregates and branched fibril-like structures. On the contrary, Cu2+ ions play a relevant role only during the heating treatment by activating immediately after incubation the aggregation evolution, increasing the aggregation rate and favouring the formation both of a higher number of aggregated species and higher growth of cross-beta structures. In conclusion, the chemical and physical approach used in studying the heat-induced structural changes in metal-BLG systems was successful, as verify on other systems [2], since it allowed to identify some amino acid residues reasonably involved in the BLG aggregation process, so elucidating the molecular mechanisms favouring the formation of fibrils and affecting their morphology.
A joint chemical and physical characterisation of thermal aggregation of beta-lactoglobulin modulated by metal ions
Armida Torreggiani;
2014
Abstract
Molecular basis of the role played by Cu2+ and Zn2+ ions during the thermal aggregation processes of beta-lactoglobulin (BLG) were studied by using a joint application of different techniques [1]. In particular, Raman spectroscopy was very useful in identifying the different effects caused by the two metals at molecular level (i.e. changes in His protonation state, disulfides bridge conformation, and micro-environment of aromatic residues), evidencing the primary importance of the protein charge distribution during the aggregation process. In particular, changes in His protonation were revealed by the curve fitting analysis of the 1080-920 cm-1 Raman region (Figure 1). In the native BLG the two His residues are in the tautomeric I form (100%), as indicated by the presence of the marker band at ?990 cm-1. After the thermal treatment, also the cationic form of His (His+) gave a small contribution, as suggested by a new component visible at 995 cm-1. A similar trend was obtained in the presence of both Zn2+ and Cu2+ ions, although the contribution of the component due to the His+ form (at ?996 cm-1) was more relevant in the presence of Zn2+ ions (about 30 %). Both metal ions are able to act on protein charge distribution and favour the protein aggregation, but Zn2+ is able to alter the natural conformational state of BLG, causing a slight unfolding. The latter, in addition to a more relevant redistribution of charges induced by Zn2+, gives rise to a different screening of electrostatic interactions between charged BLG molecules, favouring the formation of bigger aggregates and branched fibril-like structures. On the contrary, Cu2+ ions play a relevant role only during the heating treatment by activating immediately after incubation the aggregation evolution, increasing the aggregation rate and favouring the formation both of a higher number of aggregated species and higher growth of cross-beta structures. In conclusion, the chemical and physical approach used in studying the heat-induced structural changes in metal-BLG systems was successful, as verify on other systems [2], since it allowed to identify some amino acid residues reasonably involved in the BLG aggregation process, so elucidating the molecular mechanisms favouring the formation of fibrils and affecting their morphology.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
