NMR Solution Structure of Rat Aβ(1-16): Toward Understanding the Mechanism of Rats' Resistance to Alzheimer's Disease

In an attempt to reveal the mechanism of rats' resistance to Alzheimer's disease, we determined the structure of the metal-binding domain 1-16 of rat beta-amyloid (rat A beta(1-16)) in solution in the absence and presence of zinc ions. A zinc-induced dimerization of the domain was detected. The zinc coordination site was found to involve residues His-6 and His-14 of both peptide chains. We used experimental restraints obtained from analyses of NMR and isothermal titration calorimetry data to perform structure calculations. The calculations employed an explicit water environment and a simulated annealing molecular-dynamics protocol followed by quantum-mechanical/molecular-mechanical optimization. We found that the C-tails of the two polypeptide chains of the rat A beta(1-16) dimer are oriented in opposite directions to each other, which hinders the assembly of rat A beta dimers into oligomeric aggregates. Thus, the differences in the structure of zinc-binding sites of human and rat A beta(1-16), their ability to form regular cross-monomer bonds, and the orientation of their hydrophobic C-tails could be responsible for the resistance of rats to Alzheimer's disease.