Aluminum Interaction with Glutamate and α-Ketoglutarate: A Computational Study

Theoretical characterization of Al(III) binding to KSPVPKSPVEEKG: Insights into the propensity of aluminum to interact with key sequences for neurofilament formation

Classical molecular dynamic simulations and density functional theory are used to unveil the interaction of aluminum with various phosphorylated derivatives of the fragment KSPVPKSPVEEKG (NF13), a major multiphosphorylation domain of human neurofilament medium (NFM). Our calculations reveal the rich coordination chemistry of the resultant structures with a clear tendency of aluminum to form multidentate structures, acting as a bridging agent between different sidechains and altering the local secondary structure around the binding site. Our evaluation of binding energies allows us to determine that phosphorylation has an increase in the affinity of these peptides towards aluminum, although the interaction is not as strong as well-known chelators of aluminum in biological systems. Finally, the presence of hydroxides in the first solvation layer has a clear damping effect on the binding affinities. Our results help in elucidating the potential structures than can be formed between this exogenous neurotoxic metal and key sequences for the formation of neurofilament tangles, which are behind of some of the most important degenerative diseases.

The interaction of aluminum with catecholamine-based neurotransmitters: can the formation of these species be considered a potential risk factor for neurodegenerative diseases?

The potential neurotoxic role of Al(iii) and its proposed link with the insurgence of Alzheimer's Disease (AD) have attracted increasing interest towards the determination of the nature of bioligands that are propitious to interact with aluminum. Among them, catecholamine-based neurotransmitters have been proposed to be sensitive to the presence of this non-essential metal ion in the brain. In the present work, we characterize several aluminum-catecholamine complexes in various stoichiometries, determining their structure and thermodynamics of formation. For this purpose, we apply a recently validated computational protocol with results that show a remarkably good agreement with the available experimental data. In particular, we employ Density Functional Theory (DFT) in conjunction with continuum solvation models to calculate complexation energies of aluminum for a set of four important catecholamines: l-DOPA, dopamine, noradrenaline and adrenaline. In addition, by means of the Quantum Theory of Atoms in Molecules (QTAIM) and Energy Decomposition Analysis (EDA) we assessed the nature of the Al-ligand interactions, finding mainly ionic bonds with an important degree of covalent character. Our results point at the possibility of the formation of aluminum-catecholamine complexes with favorable formation energies, even when proton/aluminum competition is taken into account. Indeed, we found that these catecholamines are better aluminum binders than catechol at physiological pH, because of the electron withdrawing effect of the positively-charged amine that decreases their deprotonation penalty with respect to catechol. However, overall, our results show that, in an open biological environment, the formation of Al-catecholamine complexes is not thermodynamically competitive when compared with the formation of other aluminum species in solution such as Al-hydroxide, or when considering other endogenous/exogenous Al(iii) ligands such as citrate, deferiprone and EDTA. In summary, we rule out the possibility, suggested by some authors, that the formation of Al-catecholamine complexes in solution might be behind some of the toxic roles attributed to aluminum in the brain. An up-to-date view of the catecholamine biosynthesis pathway with sites of aluminum interference (according to the current literature) is presented. Alternative mechanisms that might explain the deleterious effects of this metal on the catecholamine route are thoroughly discussed, and new hypotheses that should be investigated in future are proposed.

Does phosphorylation increase the binding affinity of aluminum? A computational study on the aluminum interaction with serine and O-phosphoserine

Several toxic effects arise from aluminum's presence in living systems, one of these effects is to alter the natural role of enzymes and non-enzyme proteins. Aluminum promotes the hyperphosphorylation of normal proteins. In order to assess the aluminum-binding abilities of phosphorylated proteins and peptides, the interaction of aluminum at different pH with serine and phosphoserine is studied by a Density Functional Theory study, combined with polarizable continuum models to account for bulk solvent effects, and the electronic structure of selected complexes are analyzed by Quantum Theory of "Atoms in Molecules". Our results confirm the high ability of aluminum to bind polypeptides as the pH lowers. Moreover, the phosphorylation of the building blocks increases the affinity for aluminum, in particular at physiological pH. Finally, aluminum shows a tendency to be chelated forming different size rings.

Aluminium ion-promoted radical-scavenging reaction of methylated hydroquinone derivatives

The effect of the aluminium ion (Al(3+)) on the scavenging reaction of a 2,2-diphenyl-1-picrylhydrazyl radical (DPPH˙), as a reactivity model of reactive oxygen species, with hydroquinone (QH2) and its methylated derivatives (MenQH2, n = 1-4) was investigated using stopped-flow and electrochemical techniques in a hydroalcoholic medium. The second-order rate constants (k) for the DPPH˙-scavenging reaction of the hydroquinones increased with the increasing number of methyl substituents. Upon addition of Al(3+), the k values significantly increased depending on the concentration of Al(3+). Such an accelerating effect of Al(3+) on the DPPH˙-scavenging rates of the hydroquinones results from the remarkable positive shift of the one-electron reduction potential (Ered) of DPPH˙ in the presence of Al(3+). These results demonstrate that Al(3+), a strong Lewis acid, can act as a radical-scavenging promoter by stabilising the one-electron reduced species of the radical, although Al(3+) is reported not only to act as a pro-oxidant but also to strongly interact with biomolecules, showing toxicities.

Tuning the affinity of catechols and salicylic acids towards Al(iii): characterization of Al–chelator interactions

Aluminum is a non-essential element in the human body with unclear harmful effects; therefore, the design and tuning of new and efficient Al(iii) chelating agents is a subject of paramount importance nowadays.

A computational study on interaction of aluminum withd-glucose 6-phosphate for various stoichiometries

The interaction of aluminum with glucose 6-phosphate is thought to disrupt key processes of the glucide metabolism in cells. Complex and rich aluminum chelation chemistry is found in Aluminum-glucose 6-phosphate speciation study.

Phosphorylation promotes Al(iii) binding to proteins: GEGEGSGG as a case study

Aluminum, the third most abundant element in the Earth's crust and one of the key industrial components of our everyday life, has been associated with several neurodegenerative diseases due to its ability to promote neurofilament tangles and β-amyloid peptide aggregation.

Aluminum and its effect in the equilibrium between folded/unfolded conformation of NADH

Nicotinamide adenine dinucleotide (NADH) is one of the most abundant cofactor employed by proteins and enzymes. The molecule is formed by two nucleotides that can lead to two main conformations: folded/closed and unfolded/open. Experimentally, it has been determined that the closed form is about 2 kcal/mol more stable than the open formed. Computationally, a correct description of the NADH unfolding process is challenging due to different reasons: 1) The unfolding process shows a very low energy difference between the two conformations 2) The molecule can form a high number of internal hydrogen bond interactions 3) Subtle effects such as dispersion may be important. In order to tackle all these effects, we have employed a number of different state of the art computational techniques, including: a) well-tempered metadynamics, b) geometry optimizations, and c) Quantum Theory of Atoms in Molecules (QTAIM) calculations, to investigate the conformational change of NADH in solution and interacting with aluminum. All the results indicate that aluminum indeed favors the closed conformation of NADH, due mainly to the formation of a more rigid structure through key hydrogen bond interactions.