ИСТИНА

According to the widely accepted amyloid hypothesis, the key pathogenic process of Alzheimer’s disease is the transition of soluble beta-amyloid (Aβ) monomer, first into neurotoxic oligomers and then into insoluble fibrillar polymeric aggregates, which form the amyloid plaques. The details of the molecular mechanism of this aggregation remain unknown. However it has been found that zinc and copper ions play a critical role in this pathological transition. Aβ metal binding domain (MBD, 1-16) mediates zinc-induced conglutination of human Aβ and leads to further formation of stable Aβ aggregates with ordered monomer chain packing. As opposed to other mammals, rats and mice are invulnerable to Alzheimer's disease. The key role in such resistance could be the three amino acid substitutions (R5G, Y10F, H13R) in the MBD, which are the only differences between the human and rodent Aβ sequences. In order to investigate possible molecular mechanisms rodent resistance to pathogenic Aβ aggregation, the structure of the complex of rat Aβ MBD was obtained in the presence of Zn2+ ions in aqueous solution and at a physiological pH. The amino acids which participate in zinc ion coordination were determined by two independent methods - NMR and isothermal titration calorimetry (ITC). A zinc-induced dimerization of the domain was detected. The zinc coordination site was found to involve residues His6 and His14 of both peptide chains. Experimental restraints obtained from analyses of the NMR and ITC data were used in structure calculations using an explicit water environment and simulated annealing MD protocol optimized for short flexible peptides, followed by QM/MM optimization. Observed differences between the human and rat Aβ(1-16) in the structure of their zinc binding sites, the capability to form regular cross-monomer interactions, and in the orientation of the hydrophobic C-tails could be responsible for the rats’ resistance to Alzheimer’s disease. Research is supported by the Russian Foundation for Basic Research (grant 11-04-01367) and the Russian Federal Program (contract 11.519.11.2008). The supercomputer SKIF "Chebyshev" of Moscow University was used for the calculations.