Inhibition of heat-induced protein aggregation by zirconium phthalocyanines

Specific proteins found in food sources tend to aggregate into fibrils under heat treatment; studying these aggregation processes and developing tools to control protein heat-induced aggregation is an active area of research. Phthalocyanine complexes are known to exhibit antiprionic and anti-fibrillogenic activity. Thus, the anti-fibrillogenic effect of a series of Zr phthalocyanines with different out-of-plane coordinated ligands, namely positively charged (PcZrLys₂ ), negatively charged (PcZrCitr₂ ), and group able to form disulfide bridges (PcZrS₂ ), on the heat-induced aggregation of such proteins as BLG, insulin, and lysozyme was studied. The inhibition of reaction activity up to about 90% was observed in the presence of these compounds for all proteins. The effective concentration of the inhibitor was calculated for the compound with the highest activity (PcZrS₂ ) to be 10.6 ± 3.6 and 7.3 ± 1.2 μM/L, respectively. Fluorescence spectroscopy studies demonstrated similar binding constants of three phthalocyanines binding with BLG globule. This is consistent with the results of molecular dynamics simulation, which imply the interaction of the globule with the tetrapyrrole macrocycle of phthalocyanine, leading to the globule stabilization. At the same time, TEM shows that in the presence of phthalocyanine PcZrS₂ , thinner and longer fibrils were formed compared to control in all three proteins (BLG, insulin, and lysozyme). Thus, we can conclude that phthalocyanine PcZrS₂ affects the amyloid aggregation's general mechanism, which is typical for proteins of different structures. Therefore, the phthalocyanine PcZrS₂ is proposed as an anti-amyloidogenic agent suppressing heat-induced aggregation of proteins of different structures, making it potentially suitable for application in the food industry.