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Amyloid-β (Aβ) is a peptide formed by 39–43 amino acids, heterogenous by the length of its C-terminus. Aβ constitutes a subnanomolar monomeric component of human biological fluids; however, in sporadic variants of Alzheimer's disease (AD), it forms soluble neurotoxic oligomers and accumulates as insoluble extracellular polymeric aggregates (amyloid plaques) in the brain tissues. The plaque formation is controlled by zinc ions; therefore, abnormal interactions between the ions and Aβ seem to take part in the triggering of sporadic AD. The amyloid plaques contain various Aβ isoforms, among which the most common is Aβ with an isoaspartate in position 7 (isoD7). The spontaneous conversion of D7 to isoD7 is associated with Aβ aging. Aβ molecules with isoD7 (isoD7-Aβ) easily undergo zinc-dependent oligomerization, and upon administration to transgenic animals (mice, nematodes) used for AD modeling, act as zinc-dependent seeds of the pathological aggregation of Aβ. The formation of zinc-bound homo- and hetero-oligomers with the participation of isoD7-Aβ is based on the rigidly structured segment 11-EVHH-14, located in the Aβ metal binding domain (Aβ16). Some hereditary variants of AD are associated with familial mutations within the domain. Among these, the most susceptible to zinc-dependent oligomerization is Aβ with Taiwan (D7H) mutation (D7H-Aβ). In this study, the D7H-Aβ metal binding domain (D7H-Aβ16) has been used as a model to establish the molecular mechanism of zinc-induced D7H-Aβ oligomerization through turbidimetry, dynamic light scattering, isothermal titration calorimetry, mass spectrometry, and computer modelling. Additionally, the modeling data showed that a molecule of D7H-Aβ, as well as isoD7-Aβ in combination with two Aβ molecules, renders a stable zinc-induced heterotrimer. The trimers are held together by intermolecular interfaces via zinc ions, with the primary interfaces formed by 11-EVHH-14 sites of the interacting trimer subunits. In summary, the obtained results confirm the role of the 11-EVHH-14 region as a structure and function determinant for the zinc-dependent oligomerization of all known Aβ species (including various chemically modified isoforms and AD-associated mutants) and point at this region as a potent target for drugs aimed to stop amyloid plaque formation in both sporadic and hereditary variants of AD. [ABSTRACT FROM AUTHOR]

We previously showed that the metal-binding domain 1–16 of intact amyloid-beta (Aβ) is involved in interactions with a number of proteins from the cytosolic fraction of SK-N-SH human neuroblastoma cells in a zinc-dependent manner only. It is known that hereditary mutations in the Aβ metal-binding domain (Aβ(1–16)), which accelerate the development of Alzheimer's disease and post-translational modifications of amino acid residues, can significantly affect the domain's structure in the presence of zinc ions. In this work, using the molecular fishing methodology for Aβ(1–16) isoforms with the Taiwanese mutation (D7H) and a phosphorylated Ser8 residue, proteins from the cytosol of SK-N-SH cells were found that are able to form zinc-dependent non-covalent complexes with these domains. The partner proteins identified for these isoforms differed from those for intact Aβ(1–16). In contrast, the Aβ(1–16) isoform with the English mutation (H6R) and the Aβ(1–16) isoform containing both an isomerized Asp7 residue and phosphorylated Ser8 residue did not interact with cytosolic proteins. The results are useful for developing methods for rational modulation of protein-protein interactions involving natural isoforms of beta-amyloid, and also indicate the possible role of beta-amyloid with phosphorylated Ser8 as a molecule involved in normal physiological processes. [ABSTRACT FROM AUTHOR]