Nanochemistry and biotechnology

Binding of phthalocyanines to beta-lactoglobulin: first step to inhibition of amyloid aggregation 
Losytskyy M.Y.1, Chernii S.V.1, Tretyakova I.M.2, Chernii V.Y.2, Kovalska V.B.1
1 Institute of Molecular Biology and Genetics NASU, Zabolotnogo Str. 150, Kyiv, 03680, Ukraine. 
E-mail: mlosytskyy@gmail.com
2 V.I. Vernadsky Institute of General and Inorganic Chemistry NASU, Palladina Ave. 32/34, Kyiv, 03142, Ukraine.

Amyloid fibrillar aggregates are rigid insoluble structures formed as the result of proteins misfolding. These structures are present in tissues in the case of neurodegenerative deceases (e.g. Alzheimer’s or Parkinson’s ones), but also appear during the food processing. An important milk whey protein beta-lactoglobulin (BLG) forms amyloid aggregates under certain conditions, particularly during milk processing. Since amyloid aggregates are not welcome in dairy products, the ways of inhibition of such aggregation should be studied. Formation of complex between chaperone-like ligand molecule and native form of the protein could be one of the ways to inhibit protein aggregation. It was previously reported that phthalocyanines are able to stabilize protein conformation and efficiently inhibit their amyloid aggregation. So, phthalocyanines could be studied as such chaperone-like ligands. 
We have shown that zirconium phthalocyanines containing out-of-plane ligands bearing negative charge (citric acid residues), positive charge (lysine residues) and those able to form disulfide bridges (mercapto-groups) make different effect on aggregation of BLG in acidic solution (0.1 M HCl). This means that the nature of out-of-plane ligand strongly affects the phthalocyanine binding with denatured BLG. Here, binding of these compounds with native BLG in Tris-HCl buffer (pH 7.9) was studied. Fluorescence intensity increase (in about 20 times) of all three phthalocyanines in the presence of BLG points to the formation of their complex with native BLG. Equilibrium constant of phthalocyanine-BLG binding was estimated; its value was close for all studied compounds (near 3×105 M-1). Thus we could suppose that the phthalocyanine binding to native BLG at pH 7.9 is mainly due to tetraindole macrocycle of phthalocyanine with only little effect of out-of-plane ligands. 

The study was supported by CRDF Global grant #65501.