Amyloid deposits within the cerebral tissue constitute a characteristic lesion associated with Alzheimer disease. They mainly consist of the amyloid peptide Abeta and display an abnormal content in Zn(2+) ions, together with many truncated, isomerized, and racemized forms of Abeta. The region 1-16 of Abeta can be considered the minimal zinc-binding domain and contains two aspartates subject to protein aging. The influence of zinc binding and protein aging related modifications on the conformation of this region of Abeta is of importance given the potentiality of this domain to constitute a therapeutic target, especially for immunization approaches. In this study, we determined from NMR data the solution structure of the Abeta-(1-16)-Zn(2+) complex in aqueous solution at pH 6.5. The residues His(6), His(13), and His(14) and the Glu(11) carboxylate were identified as ligands that tetrahedrally coordinate the Zn(II) cation. In vitro aging experiments on Abeta-(1-16) led to the formation of truncated and isomerized species. The major isomer generated, Abeta-(1-16)-l-iso-Asp(7), displayed a local conformational change in the His(6)-Ser(8) region but kept a zinc binding propensity via a coordination mode involving l-iso-Asp(7). These results are discussed here with regard to Abeta fibrillogenesis and the potentiality of the region 1-16 of Abeta to be used as a therapeutic target.

Zinc-induced aggregation of amyloid-β peptide (Aβ) is a hallmark molecular feature of Alzheimer's disease. Here we provide direct thermodynamic evidence that elucidates the role of the Aβ region 6-14 as the minimal Zn(2+) binding site wherein the ion is coordinated by His(6), Glu(11), His(13), and His(14). With the help of isothermal titration calorimetry and quantum mechanics/molecular mechanics simulations, the region 11-14 was determined as the primary zinc recognition site and considered an important drug-target candidate to prevent Zn(2+)-induced aggregation of Aβ.

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Analysis of complex formation between amyloid-β fragments using surface plasmon resonance biosensing and electrospray mass spectrometry reveals that region 11-14 mediates zinc-induced dimerization of amyloid-β and may serve as a potential drug target for preventing development and progression of Alzheimer's disease.

Zinc-induced aggregation of the amyloid-β peptide (Aβ) is a hallmark molecular feature of Alzheimer's disease (AD). Recently it was shown that phosphorylation of Aβ at Ser8 promotes the formation of toxic aggregates. In this work, we have studied the impact of Ser8 phosphorylation on the mode of zinc interaction with the Aβ metal-binding domain 1-16 using isothermal titration calorimetry, electrospray ionization mass spectrometry and NMR spectroscopy. We have discovered a novel zinc binding site ((6)HDpS(8)) in the phosphorylated peptide, in which the zinc ion is coordinated by the imidazole ring of His6, the phosphate group attached to Ser8 and a backbone carbonyl group of His6 or Asp7. Interaction of the zinc ion with this site involves His6, thereby withdrawing it from the interaction pattern observed in the non-modified peptide. This event was found to stimulate dimerization of peptide chains through the (11)EVHH(14) site, where the zinc ion is coordinated by the two pairs of Glu11 and His14 in the two peptide subunits. The proposed molecular mechanism of zinc-induced dimerization could contribute to the understanding of initiation of pathological Aβ aggregation, and the (11)EVHH(14) tetrapeptide can be considered as a promising drug target for the prevention of amyloidogenesis.

Conformational changes of Aβ peptide result in its transformation from native monomeric state to the toxic soluble dimers, oligomers and insoluble aggregates that are hallmarks of Alzheimer’s disease (AD). Interactions of zinc ions with Aβ are mediated by the N-terminal Aβ1–16 domain and appear to play a key role in AD progression. There is a range of results indicating that these interactions trigger the Aβ plaque formation. We have determined structure and functional characteristics of the metal binding domains derived from several Aβ variants and found that their zinc-induced oligomerization is governed by conformational changes in the minimal zinc binding site 6HDSGYEVHH14. The residue H6 and segment 11EVHH14, which are part of this site are crucial for formation of the two zinc-mediated interaction interfaces in Aβ. These structural determinants can be considered as promising targets for rational design of the AD-modifying drugs aimed at blocking pathological Aβ aggregation.

Chronic imbalance between production and degradation of the human amyloid-beta peptide (Abeta) is assumed to play an important role in pathogenesis of Alzheimer's disease (AD). Post-translational modifications of Abeta could influence its interactions with specifically cleaving proteases and, therefore, perturb the Abeta homeostasis. The angiotensin-converting enzyme (ACE) was previously shown to degrade non-modified Abeta in vitro and in cells. In the presented work, we investigated the effect of isomerization of Asp-7, a common non-enzymatic age-related modification found in AD-associated Abeta species, on hydrolysis of Abeta by ACE. Two synthetic peptides corresponding to the Abeta region 1-16 with either Asp or isoAsp residues in position 7 were examined as monomeric soluble substrates for the N- as well as for the C-domain of ACE. The use of matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOFMS) coupled with the (18)O-labeled internal standard approach has allowed us to show that (i) the N-domain of ACE (N-ACE), but not the C-domain, selectively cleaves the Arg-5-His-6 bond in both peptides, and that (ii) N-ACE hydrolyzes the isoAsp-7 analogue more efficiently than the non-modified one. Our results demonstrate a new endopeptidase activity of N-ACE as well as high preference of the domain to recognize and hydrolyze the isomerized Abeta species that were earlier suggested to promote AD pathogenesis. The results suggest the need for further analysis of biological effects of isomerized Abeta and its interaction with ACE in AD pathogenesis.

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