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

Abstract

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. However, the experimental characterization of aluminum speciation in vivo is a difficult task. In the present study, we develop a theoretical protocol that combines molecular dynamics simulations, clustering of structures, and density functional theory for the characterization of the binding of aluminum to the synthetic neurofilament analogue octapeptide GEGEGSGG and its phosphorylated variant. Our protocol is tested with respect to previous NMR experimental data, which allows for a full interpretation of the experimental information available and its relationship with key thermodynamic quantities. Our results demonstrate the importance of phosphorylation in the ability of a peptide to bind to aluminum. Thus, phosphorylation: (i) changes the binding pattern of aluminum to GEGEGSGG, shifting the preferential binding site from the C-terminal to S6(P); (ii) increases the binding affinity by a factor of around 15 kcal mol(-1) in free energy; and (iii) may cause significant changes in the secondary structure and stiffness of the polypeptide chain, specially in the case of bidentate binding modes. Our results shed light on the possibility of aluminum to induce aggregation of β-amyloid proteins and neurofilament tangles.

Influence of metal binding on the conformational landscape of neurofilament peptides

“…Hollender et al 87 demonstrated that phosphorylation increases the affinity of peptides for aluminum and that this interaction affects the secondary structure, using multinuclear NMR and CD spectroscopy applied to an octapeptide with one phosphorylated serine site. Computational results in our group 88 confirmed the increase in metal affinity upon phosphorylation. In the present work, we have considered a more complex system, NF13, and its serine-phosphorylated derivatives.…”

“…These calculations have proved that phosphorylated peptides show larger interaction energy than non-phosphorylated counterparts. 49,77,88 However, only a few structures show comparable interaction energies to citrate. 49 On the other hand, properly determining the last two conditions requires long molecular dynamics simulations to obtain properly converged ensembles of these systems.…”

Aluminum's preferential binding site in proteins: sidechain of amino acids versus backbone interactions

“…This type of binding motif would lead to a dramatic change on the secondary structure of the protein, altering its conformation and provoking its denaturation. However, the existence of this type of binding motif is difficult to reconcile with previous experimental [12,14] and theoretical studies [15,16] that have unequivocally established the propensity of aluminum to interact with amino acid sidechains with Al-O bonds of mainly electrostatic nature.…”

“…For instance, in the case of the experimentally and theoretically studied GEGEGSGG octapeptide we obtain different G values depending on the coordination of aluminum. [15] We have chosen three paradigmatic cases: i) N1-GEGEGSGG where aluminum interacts with only one aspartate sidechain, -33.7 kcal/mol, N6-GEGEGSGG which shows one aspartate sidechain in the first coordination shell and a second carboxylate group in the second coordination sphere, -67.9 kcal/mol, and finally, P1-GEGEGSGG with a phosphorylated serine coordinating aluminum, -78.2 kcal/mol. All cases show a more favorable interaction than with the models in which aluminum is directly interacting with the peptide backbone.…”

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

“…9 On the other hand, molecules containing phosphate groups are also a likely target for interacting with the cation. 8,[10][11][12][13][14] Due to the variety of cellular processes in which molecules containing phosphate groups are present (ATP, phosphorylated proteins, sugar phosphates, DNA, etc. ), this high affinity to form Al(III)-phosphate compounds could disrupt key processes of the cell metabolism.…”