15 research outputs found
Aluminum's preferential binding site in proteins: sidechain of amino acids versus backbone interactions
The interaction of aluminum ion Al(III) with polypeptides is a subject of paramount importance, since it is a central feature to understand its deleterious effects in biological systems. Various drastic effects have been attributed to aluminum in its interaction with polypeptides and proteins. These interactions are thought to be established mainly through the binding of aluminum to phosphorylated and non-phosphorylated amino acid sidechains. However, a new structural paradigm has recently been proposed, in which aluminum interacts directly with the backbone of the proteins, provoking drastic changes in their secondary structure and leading ultimately to their denaturation. In the present paper, we use computational methods to discuss the possibility of aluminum to interact with the backbone of peptides and compare it with the known ability of aluminum to interact with amino acid sidechains. To do so, we compare the thermodynamics of formation of prototype aluminum-backbone structures with prototype aluminum-sidechain structures, and compare these results with previous data generated in our group in which aluminum interacts with various types of polypeptides and known aluminum biochelators. Our results clearly points to a preference of aluminum towards amino acid sidechains, rather than towards the peptide backbone. Thus, structures in which aluminum is interacting with the carbonyl group are only slightly exothermic, and they become even less favorable if the interaction implies additionally the peptide nitrogen. However, structures in which aluminum is interacting with negatively-charged sidechains like aspartic acid, or phosphorylated serines are highly favored thermodynamically.Technical and human support was provided by SGI/IZO (SGIker) of UPV/EHU and European funding (ERDF and ESF). Financial support comes from UPV/EHU (PES14/35), Eusko Jaurlaritza (IT588-13) and the Spanish Ministerio de Ciencia e Innovación (MINECO/FEDER) (CTQ2015-67608-P). GdT thanks the European Union for a Ph.D. grant inside the ITN-TCCM-642294 program
Spectroscopic and Theoretical Study of CuI Binding to His111 in the Human Prion Protein Fragment 106-115
The ability of the cellular prion protein (PrPC) to bind copper in vivo points to a physiological role for PrPC in copper transport. Six copper binding sites have been identified in the nonstructured N-terminal region of human PrPC. Among these sites, the His111 site is unique in that it contains a MKHM motif that would confer interesting CuI and CuII binding properties. We have evaluated CuI coordination to the PrP(106-115) fragment of the human PrP protein, using NMR and X-ray absorption spectroscopies and electronic structure calculations. We find that Met109 and Met112 play an important role in anchoring this metal ion. CuI coordination to His111 is pH-dependent: at pH >8, 2N1O1S species are formed with one Met ligand; in the range of pH 5-8, both methionine (Met) residues bind to CuI, forming a 1N1O2S species, where N is from His111 and O is from a backbone carbonyl or a water molecule; at pH <5, only the two Met residues remain coordinated. Thus, even upon drastic changes in the chemical environment, such as those occurring during endocytosis of PrPC (decreased pH and a reducing potential), the two Met residues in the MKHM motif enable PrPC to maintain the bound CuI ions, consistent with a copper transport function for this protein. We also find that the physiologically relevant CuI-1N1O2S species activates dioxygen via an inner-sphere mechanism, likely involving the formation of a copper(II) superoxide complex. In this process, the Met residues are partially oxidized to sulfoxide; this ability to scavenge superoxide may play a role in the proposed antioxidant properties of PrPC. This study provides further insight into the CuI coordination properties of His111 in human PrPC and the molecular mechanism of oxygen activation by this site.Fil: Arcos López, Trinidad. Instituto Politécnico Nacional. Centro de Investigación y de Estudios Avanzado; MéxicoFil: Qayyum, Munzarin. University of Stanford; Estados UnidosFil: Rivillas Acevedo, Lina. Instituto Politécnico Nacional. Centro de Investigación y de Estudios Avanzado; MéxicoFil: Miotto, Marco César. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Rosario. Instituto de Investigaciones para el Descubrimiento de Fármacos de Rosario. Universidad Nacional de Rosario. Instituto de Investigaciones para el Descubrimiento de Fármacos de Rosario; Argentina. Max Planck Laboratory for Structural Biology; ArgentinaFil: Grande Aztatzi, Rafael. Instituto Politécnico Nacional. Centro de Investigación y de Estudios Avanzado; MéxicoFil: Fernandez, Claudio Oscar. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Rosario. Instituto de Investigaciones para el Descubrimiento de Fármacos de Rosario. Universidad Nacional de Rosario. Instituto de Investigaciones para el Descubrimiento de Fármacos de Rosario; Argentina. Max Planck Laboratory for Structural Biology; ArgentinaFil: Hedman, Britt. University of Stanford; Estados UnidosFil: Hodgson, Keith O.. University of Stanford; Estados UnidosFil: Vela, Alberto. Instituto Politécnico Nacional. Centro de Investigación y de Estudios Avanzado; MéxicoFil: Solomon, Edward I.. University of Stanford; Estados UnidosFil: Quintanar, Liliana. Instituto Politécnico Nacional. Centro de Investigación y de Estudios Avanzado; Méxic
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.Financial support comes from UPV/EHU (PES14/35),
Eusko Jaurlaritza (IT588-13) and the Spanish Ministerio de Ciencia e Innovación (CTQ2015-67608-P
Planar pentacoordinate carbons in CBe5(4-) derivatives
The potential energy surfaces of a series of clusters with formula CBe5Lin(n-4) (n = 1 to 5) have been systematically explored. Our computations show that the lithium cations preserve the CBe5(4-) pentagon, such that the global minimum structure for these series of clusters has a planar pentacoordinate carbon (ppC) atom. The systems are primarily connected via a network of multicenter σ-bonds, in which the C atom acts as σ-acceptor and this acceptance of charge is balanced by the donation of the 2pz electrons to the π-cloud. The induced magnetic field analysis suggests that the clusters with formula CBe5Lin(n-4) (n = 1 to 5) are fully delocalized. The fact that these ppC-containing clusters are the lowest-energy forms on the corresponding potential energy surfaces raises expectations that these species can be prepared experimentally in the gas phase
Structural Models for Cu(II) Bound to the Fragment 92–96 of the Human Prion Protein
The prion protein (PrP<sup>C</sup>) binds Cu(II) in its
N-terminal
region, and it is associated to a group of neurodegenerative diseases
termed transmissible spongiform encephalopaties (TSEs). The isoform
PrP<sup>Sc</sup>, derived from the normal PrP<sup>C</sup>, is the
pathogenic agent of TSEs. Using spectroscopic techniques (UV–vis
absorption, circular dichroism, and electron paramagnetic resonance)
and electronic structure calculations, we obtained a structural description
for the different pH-dependent binding modes of Cu(II) to the PrP(92–96)
fragment. We have also evaluated the possibility of water molecule
ligation to the His96-bound copper ion. Geometry-optimized structural
models that reproduce the spectroscopic features of these complexes
are presented. Two Cu(II) binding modes are relevant at physiological
pH: 4N and 3NO equatorial coordination modes; these are best described
by models with no participation of water molecules in the coordination
sphere of the metal ion. In contrast, the 2N2O and N3O coordination
modes that are formed at lower pH involve the coordination of an axial
water molecule. This study underscores the importance of including
explicit water molecules when modeling copper binding sites in PrP<sup>C</sup>
Oxidation of Acid, Base, and Amide Side-Chain Amino Acid Derivatives via Hydroxyl Radical
Hydroxyl radical (<sup>•</sup>OH) is known to
be highly reactive. Herein, we analyze the oxidation of acid (Asp
and Glu), base (Arg and Lys), and amide (Asn and Gln) containing amino
acid derivatives by the consecutive attack of two <sup>•</sup>OH. In this work, we study the reaction pathway by means of density
functional theory. The oxidation mechanism is divided into two steps:
(1) the first <sup>•</sup>OH can abstract a H atom or an electron,
leading to a radical amino acid derivative, which is the intermediate
of the reaction and (2) the second <sup>•</sup>OH can abstract
another H atom or add itself to the formed radical, rendering the
final oxidized products. The studied second attack of <sup>•</sup>OH is applicable to situations where high concentration of <sup>•</sup>OH is found, e.g., in vitro. Carbonyls are the best known oxidation
products for these reactions. This work includes solvent dielectric
and confirmation’s effects of the reaction, showing that both
are negligible. Overall, the most favored intermediates of the oxidation
process at the side chain correspond to the secondary radicals stabilized
by hyperconjugation. Intermediates show to be more stable in those
cases where the spin density of the unpaired electron is lowered.
Alcohols formed at the side chains are the most favored products,
followed by the double-bond-containing ones. Interestingly, Arg and
Lys side-chain scission leads to the most favored carbonyl-containing
oxidation products, in line with experimental results
Oxidation of Acid, Base, and Amide Side-Chain Amino Acid Derivatives via Hydroxyl Radical
Hydroxyl radical (<sup>•</sup>OH) is known to
be highly reactive. Herein, we analyze the oxidation of acid (Asp
and Glu), base (Arg and Lys), and amide (Asn and Gln) containing amino
acid derivatives by the consecutive attack of two <sup>•</sup>OH. In this work, we study the reaction pathway by means of density
functional theory. The oxidation mechanism is divided into two steps:
(1) the first <sup>•</sup>OH can abstract a H atom or an electron,
leading to a radical amino acid derivative, which is the intermediate
of the reaction and (2) the second <sup>•</sup>OH can abstract
another H atom or add itself to the formed radical, rendering the
final oxidized products. The studied second attack of <sup>•</sup>OH is applicable to situations where high concentration of <sup>•</sup>OH is found, e.g., in vitro. Carbonyls are the best known oxidation
products for these reactions. This work includes solvent dielectric
and confirmation’s effects of the reaction, showing that both
are negligible. Overall, the most favored intermediates of the oxidation
process at the side chain correspond to the secondary radicals stabilized
by hyperconjugation. Intermediates show to be more stable in those
cases where the spin density of the unpaired electron is lowered.
Alcohols formed at the side chains are the most favored products,
followed by the double-bond-containing ones. Interestingly, Arg and
Lys side-chain scission leads to the most favored carbonyl-containing
oxidation products, in line with experimental results
Insights into the Oxygen-Based Ligand of the Low pH Component of the Cu<sup>2+</sup>-Amyloid‑β Complex
In spite of significant experimental
effort dedicated to the study
of Cu<sup>2+</sup> binding to the amyloid beta (Aβ) peptide,
involved in Alzheimer’s disease, the nature of the oxygen-based
ligand in the low pH component of the Cu<sup>2+</sup>-Aβ(1–16)
complex is still under debate. This study reports density-functional-theory-based
calculations that explore the potential energy surface of Cu<sup>2+</sup> complexes including N and O ligands at the N-terminus of the Aβ
peptide, with a focus on evaluating the role of Asp1 carboxylate in
copper coordination. Model conformers including 3, 6, and 17 amino
acids have been used to systematically study several aspects of the
Cu<sup>2+</sup>-coordination such as the Asp1 side chain conformation,
local peptide backbone geometry, electrostatic and/or hydrogen bond
interactions, and number and availability of Cu<sup>2+</sup> ligands.
Our results show that the Asp1 peptide carbonyl binds to Cu<sup>2+</sup> only if the coordination number is less than four. In contrast,
if four ligands are available, the most stable structures include
the Asp1 carboxylate in equatorial position instead of the Asp1 carbonyl
group. The two lowest energy Cu<sup>2+</sup>-Aβ(1–17)
models involve Asp1 COO<sup>–</sup>, the N-terminus, and His6
and His14 as equatorial ligands, with either a carbonyl or a water
molecule in the axial position. These models are in good agreement
with experimental data reported for component I of the Cu<sup>2+</sup>-Aβ(1–16) complex, including EXAFS- and X-ray-derived
Cu<sup>2+</sup>–ligand distances, Cu<sup>2+</sup> EPR parameters,
and <sup>14</sup>N and <sup>13</sup>C superhyperfine couplings. Our
results suggest that at low pH, Cu<sup>2+</sup>-Aβ species with
Asp1 carboxylate equatorial coordination coexist with species coordinating
the Asp1 carbonyl. Understanding the bonding mechanism in these species
is relevant to gain a deeper insight on the molecular processes involving
copper-amyloid-β complexes, such as aggregation and redox activity
On the nature of CH<sub>6</sub><sup>2+</sup>
992-995The
meta-stability of the hexacoordinate CH62+ dication in
the gas phase is confirmed by a detailed computational exploration of its
potential energy surface, using a modified “Kick” heuristic methodology and by
Born-Oppenheimer Molecular-Dynamics simulations to assess its kinetic
persistence. <span style="mso-bidi-font-family:Arial;
color:#222222;background:white;mso-fareast-language:ES" lang="EN-GB">The transition states
for deprotonation, decomposition into CH3+ and H3+,
hydrogen scrambling, and H-H rotation are found. In addition, a nearly perfect
correlation between the protonation affinities and their coordination number is
obtained.
</span