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Francesco Luigi Gervasio

Publications and source records attributed to Francesco Luigi Gervasio.

14 recordsLinked to original sources
PubMed2007

Charge localization in stacked radical cation DNA base pairs and the benzene dimer studied by self-interaction corrected density-functional theory.

The incomplete cancellation of the electron self-interaction can be a serious shortcoming of density-functional theory especially when treating odd-electron systems. In this work, several popular and potentially viable correction schemes are applied in order to characterize the electronic structure of stacked molecular pairs, consisting of a neutral molecule and adjacent radical cation, as a function of separation distance. The unphysical sharing of the positive charge between adjacent molecules separated by 6-7 A is corrected for by applying a new empirical scheme proposed by VandeVondele and Sprik [Phys. Chem. Chem. Phys. 2005, 7, 1363] with a unique choice of parameters. This method is subsequently applied to characterize the electronic structure of two neighboring guanines excised from a canonical Arnott B-DNA structure and will be used in future investigations of certain model DNA fibers.

Base Pairing↗
PubMed2006

Free-energy landscape for beta hairpin folding from combined parallel tempering and metadynamics.

We develop a new free-energy method, based on the combination of parallel tempering and metadynamics, and apply this method to the calculation of the free-energy landscape of the folding beta hairpin in explicit water. We show that the combined method greatly improves the performance of both parallel tempering and metadynamics. In particular, we are able to sample the high free-energy regions, which are not accessible with conventional parallel tempering. We use our results to calculate the difference in entropy and enthalpy between the folded and the unfolded state and to characterize the most populated configurations in the relevant free-energy basins.

Algorithms↗
PubMed2006

Exploring the gating mechanism in the ClC chloride channel via metadynamics.

Computer simulations have been used to probe the gating mechanism in the Salmonella serovar typhimurium chloride channel (st-ClC). Specifically, the recently developed metadynamics methodology has been exploited to construct free energy surfaces as a function of the positions of either one or two chloride ions inside the pore, the position and protonation state of the key E148 residue, and the number of water molecules coordinating the translocating ions. The present calculations confirm the multi-ion mechanism in which an ion-push-ion effect lowers the main barriers to chloride ion translocation. When a second anion is taken into account, the barrier for chloride passage through the E148 narrow region is computed to be 6 kcal/mol in the wild-type channel, irrespective of the protonation state of the E148 residue, which is shown to only affect the entrance barrier. In the E148A mutant, this barrier is much lower, amounting to 3 kcal/mol. The metadynamics calculations reported herein also demonstrate that before reaching the periplasmic solution, chloride ions have to overcome an additional barrier arising from two different effects, namely the rearrangement of their solvation shell and a flip in the backbone angles of the residues E148 and G149, which reside at the end of the alphaF helix.

Chloride Channels↗
PubMed2006

Efficient reconstruction of complex free energy landscapes by multiple walkers metadynamics.

Recently, we have introduced a new method, metadynamics, which is able to sample rarely occurring transitions and to reconstruct the free energy as a function of several variables with a controlled accuracy. This method has been successfully applied in many different fields, ranging from chemistry to biophysics and ligand docking and from material science to crystal structure prediction. We present an important development that speeds up metadynamics calculations by orders of magnitude and renders the algorithm much more robust. We use multiple interacting simulations, walkers, for exploring and reconstructing the same free energy surface. Each walker contributes to the history-dependent potential that, in metadynamics, is an estimate of the free energy. We show that the error on the reconstructed free energy does not depend on the number of walkers, leading to a fully linear scaling algorithm even on inexpensive loosely coupled clusters of PCs. In addition, we show that the accuracy and stability of the method are much improved by combining it with a weighted histogram analysis. We check the validity of our new method on a realistic application.

Algorithms↗
PubMed2005

The role of the peripheral anionic site and cation-pi interactions in the ligand penetration of the human AChE gorge.

We study the ligand (tetramethylammonium) recognition by the peripheral anionic site and its penetration of the human AChE gorge by using atomistic molecular dynamics simulations and our recently developed metadynamics method. The role of both the peripheral anionic site and the formation of cation-pi interactions in the ligand entrance are clearly shown. In particular, a simulation with the W286A mutant shows the fundamental role of this residue in anchoring the ligand at the peripheral anionic site of the enzyme and in positioning it prior to the gorge entrance. Once the ligand is properly oriented, the formation of specific and synchronized cation-pi interactions with W86, F295, and Y341 enables the gorge penetration. Eventually, the ligand is stabilized in a free energy basin by means of cation-pi interactions with W86.

Acetylcholinesterase↗
PubMed2005

Charge localization in DNA fibers.

We study by first-principles molecular dynamics the mechanism of electron hole (positive charge) localization in a laboratory realizable radical cation Z DNA crystal. We find that at room temperature structural deformation does not provide an efficient localization mechanism. Instead, we find evidence for the importance of changes in the protonation state for stabilizing the radical defect.

DNA, Z-Form↗
PubMed2005

Assessing the accuracy of metadynamics.

Metadynamics is a powerful technique that has been successfully exploited to explore the multidimensional free energy surface of complex polyatomic systems and predict transition mechanisms in very different fields, ranging from chemistry and solid-state physics to biophysics. We here derive an explicit expression for the accuracy of the methodology and provide a way to choose the parameters of the method in order to optimize its performance.

Journal Article↗
PubMed2005

Flexible docking in solution using metadynamics.

We apply our recently developed metadynamics method to the docking of ligands on flexible receptors in water solution. This method mimics the real dynamics of a ligand exiting or entering an enzyme and in so doing reconstructs the free energy surface. We apply it to four docking cases: beta-trypsin/benzamidine, beta-trypsin/chlorobenzamidine, immunoglobulin McPC-603/phosphocholine, and cyclin-dependent kinase 2/staurosporine. In every case studied, the method is able to predict the docked geometry and the free energy of docking. Its added value with respect to many other available methods is that it reconstructs the complete free energy surface, including all the relevant minima and the barriers between them.

Benzamidines↗
PubMed2004

Influence of DNA structure on the reactivity of the guanine radical cation.

Oxidative damage of DNA via radical cation formation is a common cause of mutagenesis, cancer and of the physiological changes associated with aging. By using state-of-the-art ab initio molecular dynamics simulations, we study the mechanism that guides the first steps of this process. In the mechanism proposed here, guanine, which among the bases has the lowest oxidation potential, and the phosphate backbone play a crucial role. We found that the rate limiting step is the water protolysis. We illuminate the role of the local environment in considerably lowering the barrier. Of particular relevance in this respect is the role of the phosphate backbone.

Cytosine↗
PubMed2004

Inter-residue and solvent-residue interactions in proteins: a statistical study on experimental structures.

A large set of protein structures resolved by X-ray or NMR techniques has been extracted from the Protein Data Bank and analyzed using statistical methods. In particular, we investigate the interactions between side chains and the interactions between solvent and side chains, pointing out on the possibility of including the solvent as part of a knowledge-based potential. The solvent-residue contacts are accounted for on the basis of the Voronoi's polyhedron analysis. Our investigation confirms the importance of hydrophobic residues in determining the protein stability. We observe that in general hydrophobic-hydrophobic interactions and, more specifically, aromatic-aromatic contacts tend to be increasingly distally separated in the primary sequence of proteins, thus connecting distinct secondary structure elements. A simple relation expressing the dependence of the protein free energy by the number of residues is proposed. Such a relation includes both the residue-residue and the solvent-residue contributions. The former is dominant for large size proteins, whereas for small sizes (number of residues less than 100) the two terms are comparable. Gapless threading experiments show that the solvent-residue knowledge-based potential yields a significant contribution with respect to discriminating the native structure of proteins. Such contribution is important especially for proteins of small size and is similar to that given by the most favorable residue-residue knowledge-based potential referring to hydrophobic-hydrophobic interactions such as isoleucine-leucine. In general, the inclusion of the solvent-residue interaction produces a relevant increase of the free energy gap between the native structures and decoys.

Amino Acids↗
PubMed2002

Electronic structure of wet DNA.

The electronic properties of a Z-DNA crystal synthesized in the laboratory are investigated by means of density-functional theory Car-Parrinello calculations. The electronic structure has a gap of only 1.28 eV. This separates a manifold of 12 occupied states which came from the pi guanine orbitals from the lowest empty states in which the electron is transferred to the Na+ from PO-4 groups and water molecules. We have evaluated the anisotropic optical conductivity. At low frequency the conductivity is dominated by the pi-->Na+ transitions. Our calculation demonstrates that the cost of introducing electron holes in wet DNA strands could be lower than previously anticipated.

Crystallization↗
PubMed2002

The nature of intermolecular interactions between aromatic amino acid residues.

The nature of intermolecular interactions between aromatic amino acid residues has been investigated by a combination of molecular dynamics and ab initio methods. The potential energy surface of various interacting pairs, including tryptophan, phenilalanine, and tyrosine, was scanned for determining all the relevant local minima by a combined molecular dynamics and conjugate gradient methodology with the AMBER force field. For each of these minima, single-point correlated ab initio calculations of the binding energy were performed. The agreement between empirical force field and ab initio binding energies of the minimum energy structures is excellent. Aromatic-aromatic interactions can be rationalized on the basis of electrostatic and van der Waals interactions, whereas charge transfer or polarization phenomena are small for all intermolecular complexes and, particularly, for stacked structures. Proteins 2002;48:117-125.

Amino Acids, Aromatic↗
PubMed2002

Stacking and T-shape competition in aromatic-aromatic amino acid interactions.

The potential of mean force of interacting aromatic amino acids is calculated using molecular dynamics simulations. The free energy surface is determined in order to study stacking and T-shape competition for phenylalanine-phenylalanine (Phe-Phe), phenylalanine-tyrosine (Phe-Tyr), and tyrosine-tyrosine (Tyr-Tyr) complexes in vacuo, water, carbon tetrachloride, and methanol. Stacked structures are favored in all solvents with the exception of the Tyr-Tyr complex in carbon tetrachloride, where T-shaped structures are also important. The effect of anchoring the two alpha-carbons (C(alpha)) at selected distances is investigated. We find that short and large C(alpha)-C(alpha) distances favor stacked and T-shaped structures, respectively. We analyze a set of 2396 protein structures resolved experimentally. Comparison of theoretical free energies for the complexes to the experimental analogue shows that Tyr-Tyr interaction occurs mainly at the protein surface, while Phe-Tyr and Phe-Phe interactions are more frequent in the hydrophobic protein core. This is confirmed by the Voronoi polyhedron analysis on the database protein structures. As found from the free energy calculation, analysis of the protein database has shown that proximal and distal interacting aromatic residues are predominantly stacked and T-shaped, respectively.

Computer Simulation↗