| 1. |
- Genheden, Samuel, et al.
(författare)
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Accurate Predictions of Nonpolar Solvation Free Energies Require Explicit Consideration of Binding-Site Hydration
- 2011
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Ingår i: Journal of the American Chemical Society. - : American Chemical Society (ACS). - 1520-5126 .- 0002-7863. ; 133:33, s. 13081-13092
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Tidskriftsartikel (refereegranskat)abstract
- Continuum solvation methods are frequently used to increase the efficiency of computational methods to estimate free energies. In this paper, we have evaluated how well such methods estimate the nonpolar solvation free-energy change when a ligand binds to a protein. Three different continuum methods at various levels of approximation were considered, viz., the polarized continuum model (PCM), a method based on cavity and dispersion terms (CD), and a method based on a linear relation to the solvent-accessible surface area (SASA). Formally rigorous double-decoupling thermodynamic integration was used as a benchmark for the continuum methods. We have studied four protein-ligand complexes with binding sites of varying solvent exposure, namely the binding of phenol to ferritin, a biotin analogue to avidin, 2-aminobenzimidazole to trypsin, and a substituted galactoside to galectin-3. For ferritin and avidin, which have relatively hidden binding sites, rather accurate nonpolar solvation free energies could be obtained with the continuum methods if the binding site is prohibited to be filled by continuum water in the unbound state, even though the simulations and experiments show that the ligand replaces several water molecules upon binding. For the more solvent exposed binding sites of trypsin and galectin-3, no accurate continuum estimates could be obtained, even if the binding site was allowed or prohibited to be filled by continuum water. This shows that continuum methods fail to give accurate free energies on a wide range of systems with varying solvent exposure because they lack a microscopic picture of binding-site hydration as well as information about the entropy of water molecules that are in the binding site before the ligand binds. Consequently, binding affinity estimates based upon continuum solvation methods will give absolute binding energies that may differ by up to 200 kJ/mol depending on the method used. Moreover, even relative energies between ligands with the same scaffold may differ by up to 75 kJ/mol. We have tried to improve the continuum solvation methods by adding information about the solvent exposure of the binding site or the hydration of the binding site, and the results are promising at least for this small set of complexes.
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| 2. |
- Genheden, Samuel, et al.
(författare)
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Nonpolar Solvation Free Energies of Protein-Ligand Complexes
- 2010
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Ingår i: Journal of Chemical Theory and Computation. - : American Chemical Society (ACS). - 1549-9618 .- 1549-9626. ; 6:11, s. 3558-3568
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Tidskriftsartikel (refereegranskat)abstract
- Recent investigations have indicated that different solvation methods give qualitatively different results for the nonpolar solvation contribution to ligand-binding affinities. Therefore, we have calculated the nonpolar solvation contribution to the free energy of benzene binding to the T4 lysozyme Leu99Ala mutant using thermodynamic integration (TI) and three approximate methods. The total binding free energy was calculated with TI and then decomposed into contributions from the solvent and the solute. The nonpolar contribution from the solute was compared to approximate methods within the framework of the molecular-mechanics and generalized Born with surface area method (MM/GBSA). First, the nonpolar solvation energy was calculated with a linear relation to the solvent-accessible surface area (SASA). Second, a recent approach that divides the nonpolar solvation energy into cavity and dispersion parts was used, and third, the nonpolar solvation energy was calculated with the polarized continuum model (PCM). Surprisingly, the simple SASA estimate reproduces the TI results best. However, the reason for this is that all continuum methods assume that the benzene cavity is filled with water for the free protein, contrary to both experimental and simulation results. We present a method to avoid this assumption and then, PCM provides results that are closest to the results obtained with TI.
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| 3. |
- Hedegard, Erik Donovan, et al.
(författare)
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Multiscale Modeling of the Active Site of [Fe] Hydrogenase: The H-2 Binding Site in Open and Closed Protein Conformations
- 2015
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Ingår i: Angewandte Chemie (International edition). - : Wiley. - 1521-3773. ; 54:21, s. 6246-6250
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Tidskriftsartikel (refereegranskat)abstract
- A series of QM/MM optimizations of the full protein of [Fe] hydrogenase were performed. The FeGP cofactor has been optimized in the water-bound resting state (1), with a side-on bound dihydrogen (2), or as a hydride intermediate (3). For inclusion of H4MPT in the closed structure, advanced multiscale modeling appears to be necessary, especially to obtain reliable distances between CH-H4MPT+ and the dihydrogen (H-2) or hydride (H-) ligand in the FeGP cofactor. Inclusion of the full protein is further important for the relative energies of the two intermediates 2 and 3. We finally find that hydride transfer from 3 has a significantly higher barrier than found in previous studies neglecting the full protein environment.
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| 4. |
- Hedegard, Erik Donovan, et al.
(författare)
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Theoretical Fe-57 Mossbauer spectroscopy: isomer shifts of [Fe]- hydrogenase intermediates
- 2014
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Ingår i: Physical Chemistry Chemical Physics. - : Royal Society of Chemistry (RSC). - 1463-9084. ; 16:10, s. 4853-4863
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Tidskriftsartikel (refereegranskat)abstract
- Mossbauer spectroscopy is an indispensable spectroscopic technique and analytical tool in iron coordination chemistry. The linear correlation between the electron density at the nucleus ("contact density'') and experimental isomer shifts has been used to link calculated contact densities to experimental isomer shifts. Here we have investigated relativistic methods of systematically increasing sophistication, including the eXact 2-Component (X2C) Hamiltonian and a finite-nucleus model, for the calculation of isomer shifts of iron compounds. While being of similar accuracy as the full four-component treatment, X2C calculations are far more efficient. We find that effects of spin-orbit coupling can safely be neglected, leading to further speedup. Linear correlation plots using effective densities rather than contact densities versus experimental isomer shift lead to a correlation constant a = -0.294 a(0)(-3) mm s(-1) (PBE functional) which is close to an experimentally derived value. Isomer shifts of similar quality can thus be obtained both with and without fitting, which is not the case if one pursues a priori a non-relativistic model approach. As an application for a biologically relevant system, we have studied three recently proposed [ Fe]-hydrogenase intermediates. The structures of these intermediates were extracted from QM/MM calculations using large QM regions surrounded by the full enzyme and a solvation shell of water molecules. We show that a comparison between calculated and experimentally observed isomer shifts can be used to discriminate between different intermediates, whereas calculated atomic charges do not necessarily correlate with Mossbauer isomer shifts. Detailed analysis reveals that the difference in isomer shifts between two intermediates is due to an overlap effect.
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| 5. |
- Kongsted, Jacob, et al.
(författare)
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An improved method to predict the entropy term with the MM/PBSA approach.
- 2009
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Ingår i: Journal of Computer-Aided Molecular Design. - : Springer Science and Business Media LLC. - 1573-4951 .- 0920-654X. ; 23, s. 63-71
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Tidskriftsartikel (refereegranskat)abstract
- A method is suggested to calculate improved entropies within the MM/PBSA approach (molecular mechanics combined with Poisson-Boltzmann and surface area calculations) to estimate protein-ligand binding affinities. In the conventional approach, the protein is truncated outside ~8 A from the ligand. This system is freely minimised using a distance-dependent dielectric constant (to simulate the removed protein and solvent). However, this can lead to extensive changes in the molecular geometry, giving rise to a large standard deviation in this term. In our new approach, we introduce a buffer region ~4 A outside the truncated protein (including solvent molecules) and keep it fixed during the minimisation. Thereby, we reduce the standard deviation by a factor of 2-4, ensuring that the entropy term no longer limits the precision of the MM/PBSA predictions. The new method is tested for the binding of seven biotin analogues to avidin, eight amidinobenzyl-indole-carboxamide inhibitors to factor Xa, and two substrates to cytochrome P450 3A4 and 2C9. It is shown that it gives more stable results and often improved predictions of the relative binding affinities.
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| 6. |
- Kongsted, Jacob, et al.
(författare)
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How accurate are continuum solvation models for drug-like molecules?
- 2009
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Ingår i: Journal of Computer-Aided Molecular Design. - : Springer Science and Business Media LLC. - 1573-4951 .- 0920-654X. ; 23:7, s. 395-409
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Tidskriftsartikel (refereegranskat)abstract
- We have estimated the hydration free energy for 20 neutral drug-like molecules, as well as for three series of 6-11 inhibitors to avidin, factor Xa, and galectin-3 with four different continuum solvent approaches (the polarised continuum method the Langevin dipole method, the finite-difference solution of the Poisson equation, and the generalised Born method), and several variants of each, giving in total 24 different methods. All four types of methods have been thoroughly calibrated for a number of experimentally known small organic molecules with a mean absolute deviation (MAD) of 1-6 kJ/mol for neutral molecules and 4-30 kJ/mol for ions. However, for the drug-like molecules, the accuracy seems to be appreciably worse. The reason for this is that drug-like molecules are more polar than small organic molecules and that the uncertainty of the methods is proportional to the size of the solvation energy. Therefore, the accuracy of continuum solvation methods should be discussed in relative, rather than absolute, terms. In fact, the mean unsigned relative deviations of the best solvation methods, 0.09 for neutral and 0.05 for ionic molecules, correspond to 2-20 kJ/mol absolute error for the drug-like molecules in this investigation, or 2-3,000 in terms of binding constants. Fortunately, the accuracy of all methods can be improved if only relative energies within a series of inhibitors are considered, especially if all of them have the same net charge. Then, all except two methods give MADs of 2-5 kJ/mol (corresponding to an uncertainty of a factor of 2-7 in the binding constant). Interestingly, the generalised Born methods typically give better results than the Poison-Boltzmann methods.
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| 7. |
- Kongsted, Jacob, et al.
(författare)
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Prediction and rationalization of the pH dependence of the activity and stability of family 11 xylanases
- 2007
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Ingår i: Biochemistry. - : American Chemical Society (ACS). - 0006-2960 .- 1520-4995. ; 46:47, s. 13581-13592
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Tidskriftsartikel (refereegranskat)abstract
- This paper presents a study of the pH dependence of the activity and stability of a set of family 11 xylanases for which X-ray structures are available, using the PROPKA approach. The xylanases are traditionally divided into basic and acidic xylanases, depending on whether the catalytic acid is hydrogen bonded to an Asn or Asp residue. Using X-ray structures, the predicted pH values of optimal activity of the basic xylanases are in the range of 5.2-6.9, which is in reasonable agreement with the available experimental values of 5-6.5. In the case of acidic xylanases, there are only four X-ray structures available, and using these structures, the predicted pHs of optimal activity are in the range of 4.2-5.0, compared to an observed range of 2-4.6. The influence of dynamical fluctuations of the protein structure is investigated for Bacillus agaradhaerens and Aspergillus kawachii xylanase using molecular dynamics (MD) simulations to provide snapshots from which average values can be computed. This decreases the respective predicted pH optima from 6.2-6.7 and 4.8 to 5.3 +/- 0.3 and 4.0 +/- 0.2, respectively, which are in better agreement with the observed values of 5.6 and 2, respectively. The change is primarily due to structural fluctuations of an Arg residue near the catalytic nucleophile, which lowers its pK(a) value compared to using the X-ray structure. The MD simulations and some X-ray structures indicate that this Arg residue can form a hydrogen bond to the catalytic base, and it is hypothesized that this hydrogen bond is stabilized by an additional hydrogen bond to another Glu residue present only in acidic xylanases. Formation of such a hydrogen bond is predicted to lower the pH optimum of A. kawachii xylanase to 2.9 +/- 0.3, which is in reasonable agreement, with the observed value of 2. The predicted pH of optimal stability is in excellent agreement with the pH value at which the melting temperature (T-m) is greatest. Some correlation is observed between the pH-dependent free energy of unfolding and T-m, suggesting that the thermostability of the xylanases is partly due to a difference in residues with shifted pK(a) values. Thus, the thermostability of xylanases (and proteins in general) can perhaps be increased by mutations that introduce ionizable residues with pK(a) values significantly lower than standard values.
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| 8. |
- Rocha-Rinza, Tomas, et al.
(författare)
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Unraveling the similarity of the photoabsorption of deprotonated p-coumaric acid in the gas phase and within the photoactive yellow protein
- 2011
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Ingår i: Physical Chemistry Chemical Physics. - : Royal Society of Chemistry (RSC). - 1463-9084. ; 13:4, s. 1585-1589
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Tidskriftsartikel (refereegranskat)abstract
- Using advanced QM/MM methods, the surprisingly negligible shift of the lowest-lying bright electronic excitation of the deprotonated p-coumaric acid (pCA(-)) within the photoactive yellow protein (PYP) is shown to stem from a subtle balance between hypsochromic and bathochromic effects. More specifically, it is found that the change in the excitation energy as a consequence of the disruption of the planarity of pCA(-) inside PYP is nearly canceled out by the shift induced by the intermolecular interactions of the chromophore and the protein as a whole. These results provide important insights about the primary absorption and the tuning of the chromophore by the protein environment in PYP.
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| 9. |
- Rydberg, Patrik, et al.
(författare)
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Transition-State Docking of Flunitrazepam and Progesterone in Cytochrome P450
- 2008
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Ingår i: J.Chem.Theory Comput.. - : American Chemical Society (ACS). ; 4, s. 673-681
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Tidskriftsartikel (refereegranskat)abstract
- We have developed a method to dock a transition-state structure into the active site of an enzyme. Such an approach is more discriminative than standard docking when looking for substrates of an enzyme, because a transition state has more sterical restrictions than a nonreactive state. We use an accurate and tailored force field for the transition-state for the hydroxylation reaction in cytochrome P450, obtained with the Q2MM method. We apply this method to the docking of two drugs, progesterone and flunitrazepam, to the active sites of two human cytochromes P450, 2C9 and 3A4. We obtain a qualitative agreement compared to experiments, both for hydrogen atoms bound to the same carbon atom (for which the force-field energies are directly comparable) and for general sites on the drug molecules, if the method is combined with an estimate of the intrinsic reactivity of the various sites. However, the method does not rank all the sites correctly. It is not significantly improved if the proteins are allowed to relax locally or if it is combined with the MM/PBSA approach, which fully accounts for the protein flexibility and explicitly treats solvation and entropy effects. On the other hand our method performs better than standard docking with the GOLD software or predictions of metabolic sites with the MetaSite software.
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| 10. |
- Söderhjelm, Pär, et al.
(författare)
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Conformational Dependence of Isotropic Polarizabilities
- 2011
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Ingår i: Journal of Chemical Theory and Computation. - : American Chemical Society (ACS). - 1549-9618 .- 1549-9626. ; 7:5, s. 1404-1414
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Tidskriftsartikel (refereegranskat)abstract
- We perform a statistical and energetic analysis of atomic polarizabilities obtained with the LoProp approach for all atoms in the avidin tetramer for 70 snapshots from molecular dynamics simulations with seven different biotin analogues, and from the crystal structure of the photosynthetic reaction center (in total 560 698 individual polarizabilities). Dynamic effects give a variation of the polarizabilities of 0.09 angstrom(3) on average. Atoms at different positions in the sequence show a variation of 0.14 angstrom(3) on average, caused by the conformational dependence of the polarizabilities. This variation gives errors of 2 and 1 kJ/mol for relative conformational and ligand-binding induction energies. Averaged elementwise or atom type polarizabilities give larger errors, e.g., 9 and 7 kJ/mol, respectively, for the relative conformational energies. Therefore, we recommend that polarizabilities should be assigned atomwise (i.e., individual polarizabilities for each atom in all residues), in the same way as for charges. We provide such a set of extensively averaged polarizabilities (xAvPol) for all atoms in avidin and the photosynthetic reaction center, applicable at the B3LYP/aug-cc-pVTZ level, which is converged with respect to the basis-set limit.
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