The hydrolytic stability of the human tubulin α 1A protein fragment – a potential reason for the role of metal ions in the development of neurodegenerative diseases

Alpha-tubulin proteins are recognised as key components in the process of cell division due to their role in dimerisation and polymerisation, which results in the formation of microtubules in eukaryotes; however in the context of Alzheimer's disease (AD) and other neurodegenerative diseases (NDDs), they may also play an important role, as alterations in their structure and disintegration have been observed. The present paper investigates the 189-195 region of the human tubulin α 1A protein, in the presence of essential copper(ii) and zinc(ii) ions and the toxic nickel(ii) metal ions. The aforementioned natural protein fragment contains the -(S/T)XH- amino acid motif, whose sequences were previously identified as active sites for a metal-ion-induced, sequence-specific hydrolysis process. The solution equilibrium studies (pH-potentiometry and UV-Vis and CD spectroscopy) demonstrated that the nickel(ii) and copper(ii) complexes formed under physiological pH conditions exhibit enhanced thermodynamic stability. The RP-HPLC and MS studies confirmed the irreversible behaviour of the heptapeptide due to the formation of the intermediate and final products of the hydrolytic reaction, which were induced by the nickel(ii) and copper(ii) metal ions. In the presence of nickel(ii) ions under conditions of a pH of 8.2 and a temperature of 37 °C, the kinetic parameters of the reaction were determined. The half-life value for the formation of the intermediate product was found to be 3.70 hours, while that for the formation of the final product was 73.75 hours.