Structure-stability correlations for imine formation in aqueous solution

Iron has been implicated in Alzheimer's disease, but until now no direct proof of Fe(II) binding to the amyloid-β peptide (Aβ) has been reported. We used NMR to evidence Fe(II) coordination to full-length Aβ40 and truncated Aβ16 peptides at physiological pH and to show that the Fe(II) binding site is located in the first 16 amino-acid residues. Fe(II) caused selective broadening of some NMR peaks that was dependent on the Fe:Aβ stoichiometry and temperature. Analysis of Fe(II) broadening effect in the (1)H, (13)C, and 2D NMR data established that Asp1, Glu3, the three His, but not Tyr10 nor Met35 are the residues mainly involved in Fe(II) coordination.

Iron(II) binding to amyloid-β, the Alzheimer's peptide.

The theory and practice of proton microspeciation based on NMR-pH titrations are surveyed. Principles of bi-, tri-, tetra-, and n-protic microequilibrium systems are discussed. Evaluation methods are exemplified by case studies on bi- and tetraprotic biomolecules. Selection criteria and properties of 'reporter' NMR nuclei are described. Literature data on complete microspeciations of small ligands and site-specific basicity characterizations of peptides and proteins are critically reviewed.

Determination of microscopic acid–base parameters from NMR–pH titrations

Oxidative stress is linked to the etiology of Alzheimer’s disease (AD), the most common cause of dementia in the elderly. Redox active metal ions such as copper catalyze the production of Reactive Oxygen Species (ROS) when bound to the amyloid-b (Ab) peptide encountered in AD. We propose that this reaction proceeds through a low-populated Cu–Ab state, denoted the “catalytic in-between state” (CIBS), which is in equilibrium with the resting state (RS) of both Cu(I)–Ab and Cu(II)–Ab. The nature of this CIBS is investigated in the present work. We report the use of complementary spectroscopic methods (X-ray absorption spectroscopy, EPR and NMR) to characterize the binding of Cu to a wide series of modified peptides in the RS. ROS production by the resulting Cu–peptide complexes was evaluated using fluorescence and UV-vis based methods and led to the identification of the amino acid residues involved in the Cu–Ab CIBS species. In addition, a possible mechanism by which the ROS are produced is also proposed. These two main results are expected to affect the current vision of the ROS production mechanism by Cu–Ab but also in other diseases involving myloidogenic peptides with weakly structured copper binding sites.

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Identification of key structural features of the elusive Cu–Aβ complex that generates ROS in Alzheimer’s disease

The thermodynamic properties of the Desulfovibrio vulgaris (Hildenborough) tetrahaem cytochrome c3 (Dvc3) are rationalised by a model which involves both homotropic (e−/e−) and heterotropic (e−/H+) cooperativity. The paramagnetic shifts of a methyl group from each haem of the DVc3 have been determined in each stage of oxidation at several pH values by means of two-dimensional exchange NMR. The thermodynamic parameters are obtained by fitting the model to the NMR data and to redox titrations followed by visible spectroscopy. They show significant positive cooperativity between two of the haems whereas the remaining interactions appear to be largely electrostatic in origin. These parameters imply that the protein undergoes a proton-assisted two-electron transfer which can be used for energy transduction. Comparison with the crystal structure together with measurement of the kinetics of proton exchange suggest that the pH dependence is mediated by a charged residue(s) readily acessible to the solvent and close to haem I.

https://febs.onlinelibrary.wiley.com/doi/pdf/10.1111/j.1432-1033.1996.00723.x

M.F. Cabral

Papers

Dissociation constants of Br∅nsted acids in D2O and H2O: studies on polyaza and polyoxa-polyaza macrocycles and a general correlation