1
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Petrov D, Perthold JW, Oostenbrink C, de Groot BL, Gapsys V. Guidelines for Free-Energy Calculations Involving Charge Changes. J Chem Theory Comput 2024; 20:914-925. [PMID: 38164763 PMCID: PMC10809403 DOI: 10.1021/acs.jctc.3c00757] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/11/2023] [Revised: 11/24/2023] [Accepted: 11/27/2023] [Indexed: 01/03/2024]
Abstract
The Coulomb interactions in molecular simulations are inherently approximated due to the finite size of the molecular box sizes amenable to current-day compute power. Several methods exist for treating long-range electrostatic interactions, yet these approaches are subject to various finite-size-related artifacts. Lattice-sum methods are frequently used to approximate long-range interactions; however, these approaches also suffer from artifacts which become particularly pronounced for free-energy calculations that involve charge changes. The artifacts, however, also affect the sampling when plain simulations are performed, leading to a biased ensemble. Here, we investigate two previously described model systems to determine if artifacts continue to play a role when overall neutral boxes are considered, in the context of both free-energy calculations and sampling. We find that ensuring that no net-charge changes take place, while maintaining a neutral simulation box, may be sufficient provided that the simulation boxes are large enough. Addition of salt to the solution (when appropriate) can further alleviate the remaining artifacts in the sampling or the calculated free-energy differences. We provide practical guidelines to avoid finite-size artifacts.
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Affiliation(s)
- Drazen Petrov
- Institute
for Molecular Modeling and Simulation, Department of Material Sciences
and Process Engineering, University of Natural
Resources and Life Sciences, Vienna, Vienna 1190, Austria
| | - Jan Walther Perthold
- Institute
for Molecular Modeling and Simulation, Department of Material Sciences
and Process Engineering, University of Natural
Resources and Life Sciences, Vienna, Vienna 1190, Austria
| | - Chris Oostenbrink
- Institute
for Molecular Modeling and Simulation, Department of Material Sciences
and Process Engineering, University of Natural
Resources and Life Sciences, Vienna, Vienna 1190, Austria
- Christian
Doppler Laboratory for Molecular Informatics in the Biosciences, University of Natural Resources and Life Sciences, Vienna, Vienna 1190, Austria
| | - Bert L. de Groot
- Computational
Biomolecular Dynamics Group, Department of Theoretical and Computational
Biophysics, Max Planck Institute for Multidisciplinary
Sciences, Göttingen 37077, Germany
| | - Vytautas Gapsys
- Computational
Biomolecular Dynamics Group, Department of Theoretical and Computational
Biophysics, Max Planck Institute for Multidisciplinary
Sciences, Göttingen 37077, Germany
- Computational
Chemistry, Janssen Research & Development, Janssen Pharmaceutica N. V., Turnhoutseweg
30, Beerse B-2340, Belgium
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2
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Bignucolo O, Chipot C, Kellenberger S, Roux B. Galvani Offset Potential and Constant-pH Simulations of Membrane Proteins. J Phys Chem B 2022; 126:6868-6877. [PMID: 36049129 PMCID: PMC9483922 DOI: 10.1021/acs.jpcb.2c04593] [Citation(s) in RCA: 12] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/30/2022] [Revised: 08/17/2022] [Indexed: 02/01/2023]
Abstract
A central problem in computational biophysics is the treatment of titratable residues in molecular dynamics simulations of large biological macromolecular systems. Conventional simulation methods ascribe a fixed ionization state to titratable residues in accordance with their pKa and the pH of the system, assuming that an effective average model will be able to capture the predominant behavior of the system. While this assumption may be justifiable in many cases, it is certainly limited, and it is important to design alternative methodologies allowing a more realistic treatment. Constant-pH simulation methods provide powerful approaches to handle titratable residues more realistically by allowing the ionization state to vary statistically during the simulation. Extending the molecular mechanical (MM) potential energy function to a family of potential functions accounting for different ionization states, constant-pH simulations are designed to sample all accessible configurations and ionization states, properly weighted according to their Boltzmann factor. Because protonation and deprotonation events correspond to a change in the total charge, difficulties arise when the long-range Coulomb interaction is treated on the basis of an idealized infinite simulation model and periodic boundary conditions with particle-mesh Ewald lattice sums. Charging free-energy calculations performed under these conditions in aqueous solution depend on the Galvani potential of the bulk water phase. This has important implications for the equilibrium and nonequilibrium constant-pH simulation methods grounded in the relative free-energy difference corresponding to the protonated and unprotonated residues. Here, the effect of the Galvani potential is clarified, and a simple practical solution is introduced to address this issue in constant-pH simulations of the acid-sensing ion channel (ASIC).
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Affiliation(s)
- Olivier Bignucolo
- Department
of Biomedical Sciences, University of Lausanne, 1015 Lausanne, Switzerland
- SIB
Swiss Institute of Bioinformatics, 1015 Lausanne, Switzerland
| | - Christophe Chipot
- Department
of Biochemistry and Molecular Biology, The
University of Chicago, Chicago, Illinois 60637, United States
- Laboratoire
International Associé Centre National de la Recherche Scientifique
et University of Illinois at Urbana−Champaign, Unité
Mixte de Recherche n◦7019, Université
de Lorraine, B.P. 70239, 54506 Cedex Vandœuvre-lès-Nancy, France
- Department
of Physics, University of Illinois at Urbana−Champaign, Urbana, Illinois 61820, United States
| | - Stephan Kellenberger
- Department
of Biomedical Sciences, University of Lausanne, 1015 Lausanne, Switzerland
| | - Benoît Roux
- Department
of Biochemistry and Molecular Biology, The
University of Chicago, Chicago, Illinois 60637, United States
- Department
of Chemistry, The University of Chicago, 5735 S. Ellis Ave., Chicago, Illinois 60637, United States
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3
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Zhang Y, Jiang Y, Peng J, Zhang H. Rational Design of Nonbonded Point Charge Models for Divalent Metal Cations with Lennard-Jones 12-6 Potential. J Chem Inf Model 2021; 61:4031-4044. [PMID: 34313132 DOI: 10.1021/acs.jcim.1c00580] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
Exploring a metal-involved biochemical process at a molecular level often requires a reliable description of metal properties in aqueous solution by classical nonbonded models. An additional C4 term for considering ion-induced dipole interactions was previously proposed to supplement the widely used Lennard-Jones 12-6 potential (known as the 12-6-4 LJ-type model) with good accuracy. Here, we demonstrate an alternative to modeling divalent metal cations (M2+) with the traditional 12-6 LJ potential by developing nonbonded point charge models for use with 11 water models: TIP3P, SPC/E, SPC/Eb, TIP4P-Ew, TIP4P-D, and TIP4P/2005 and the more recent OPC3, TIP3P-FB, OPC, TIP4P-FB, and a99SB-disp. Our designed models simultaneously reproduce the experimental hydration free energy, ion-oxygen distance, and coordination number in the first hydration shell accurately for most of the metal cations, an accuracy equivalent to that of the complex 12-6-4 LJ-type and double exponential potential models. A systematic comparison with the existing M2+ models is presented as well in terms of effective ion radii, diffusion constants, water exchange rates, and ion-water interactions. Molecular dynamics simulations of metal substitution in Escherichia coli glyoxalase I variants show the great potential of our new models for metalloproteins.
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Affiliation(s)
- Yongguang Zhang
- Department of Biological Science and Engineering, School of Chemistry and Biological Engineering, University of Science and Technology Beijing, Beijing 100083, China
| | - Yang Jiang
- Department of Chemistry, Pennsylvania State University, University Park 16802, Pennsylvania, United States
| | - Jiarong Peng
- Department of Biological Science and Engineering, School of Chemistry and Biological Engineering, University of Science and Technology Beijing, Beijing 100083, China
| | - Haiyang Zhang
- Department of Biological Science and Engineering, School of Chemistry and Biological Engineering, University of Science and Technology Beijing, Beijing 100083, China
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4
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Fossat M, Zeng X, Pappu RV. Uncovering Differences in Hydration Free Energies and Structures for Model Compound Mimics of Charged Side Chains of Amino Acids. J Phys Chem B 2021; 125:4148-4161. [PMID: 33877835 PMCID: PMC8154595 DOI: 10.1021/acs.jpcb.1c01073] [Citation(s) in RCA: 38] [Impact Index Per Article: 12.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/05/2021] [Revised: 04/07/2021] [Indexed: 02/07/2023]
Abstract
Free energies of hydration are of fundamental interest for modeling and understanding conformational and phase equilibria of macromolecular solutes in aqueous phases. Of particular relevance to systems such as intrinsically disordered proteins are the free energies of hydration and hydration structures of model compounds that mimic charged side chains of Arg, Lys, Asp, and Glu. Here, we deploy a Thermodynamic Cycle-based Proton Dissociation (TCPD) approach in conjunction with data from direct measurements to obtain estimates for the free energies of hydration for model compounds that mimic the side chains of Arg+, Lys+, Asp-, and Glu-. Irrespective of the choice made for the hydration free energy of the proton, the TCPD approach reveals clear trends regarding the free energies of hydration for Arg+, Lys+, Asp-, and Glu-. These trends include asymmetries between the hydration free energies of acidic (Asp- and Glu-) and basic (Arg+ and Lys+) residues. Further, the TCPD analysis, which relies on a combination of experimental data, shows that the free energy of hydration of Arg+ is less favorable than that of Lys+. We sought a physical explanation for the TCPD-derived trends in free energies of hydration. To this end, we performed temperature-dependent calculations of free energies of hydration and analyzed hydration structures from simulations that use the polarizable Atomic Multipole Optimized Energetics for Biomolecular Applications (AMOEBA) force field and water model. At 298 K, the AMOEBA model generates estimates of free energies of hydration that are consistent with TCPD values with a free energy of hydration for the proton of ca. -259 kcal/mol. Analysis of temperature-dependent simulations leads to a structural explanation for the observed differences in free energies of hydration of ionizable residues and reveals that the heat capacity of hydration is positive for Arg+ and Lys+ and negative for Asp- and Glu-.
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Affiliation(s)
| | | | - Rohit V. Pappu
- Department of Biomedical Engineering
and Center for Science & Engineering of Living Systems, Washington University in St. Louis, St. Louis, Missouri 63130, United States
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5
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Abstract
PDZ domains contain 80-100 amino acids and bind short C-terminal sequences of target proteins. Their specificity is essential for cellular signaling pathways. We studied the binding of the Tiam1 PDZ domain to peptides derived from the C-termini of its Syndecan-1 and Caspr4 targets. We used free energy perturbation (FEP) to characterize the binding energetics of one wild-type and 17 mutant complexes by simulating 21 alchemical transformations between pairs of complexes. Thirteen complexes had known experimental affinities. FEP is a powerful tool to understand protein/ligand binding. It depends, however, on the accuracy of molecular dynamics force fields and conformational sampling. Both aspects require continued testing, especially for ionic mutations. For six mutations that did not modify the net charge, we obtained excellent agreement with experiment using the additive, AMBER ff99SB force field, with a root mean square deviation (RMSD) of 0.37 kcal/mol. For six ionic mutations that modified the net charge, agreement was also good, with one large error (3 kcal/mol) and an RMSD of 0.9 kcal/mol for the other five. The large error arose from the overstabilization of a protein/peptide salt bridge by the additive force field. Four of the ionic mutations were also simulated with the polarizable Drude force field, which represents the first test of this force field for protein/ligand binding free energy changes. The large error was eliminated and the RMS error for the four mutations was reduced from 1.8 to 1.2 kcal/mol. The overall accuracy of FEP indicates it can be used to understand PDZ/peptide binding. Importantly, our results show that for ionic mutations in buried regions, electronic polarization plays a significant role.
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6
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Hofer TS, Hünenberger PH. Absolute proton hydration free energy, surface potential of water, and redox potential of the hydrogen electrode from first principles: QM/MM MD free-energy simulations of sodium and potassium hydration. J Chem Phys 2018; 148:222814. [DOI: 10.1063/1.5000799] [Citation(s) in RCA: 60] [Impact Index Per Article: 10.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023] Open
Affiliation(s)
- Thomas S. Hofer
- Theoretical Chemistry Division, Institute of General, Inorganic and Theoretical Chemistry, Centre for Chemistry and Biomedicine, University of Innsbruck, Innrain 80-82, A-6020 Innsbruck, Austria
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7
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Lin FY, Lopes PEM, Harder E, Roux B, MacKerell AD. Polarizable Force Field for Molecular Ions Based on the Classical Drude Oscillator. J Chem Inf Model 2018; 58:993-1004. [PMID: 29624370 PMCID: PMC5975207 DOI: 10.1021/acs.jcim.8b00132] [Citation(s) in RCA: 37] [Impact Index Per Article: 6.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022]
Abstract
Development of accurate force field parameters for molecular ions in the context of a polarizable energy function based on the classical Drude oscillator is a crucial step toward an accurate polarizable model for modeling and simulations of biological macromolecules. Toward this goal we have undertaken a hierarchical approach in which force field parameter optimization is initially performed for small molecules for which experimental data exists that serve as building blocks of macromolecular systems. Small molecules representative of the ionic moieties of biological macromolecules include the cationic ammonium and methyl substituted ammonium derivatives, imidazolium, guanidinium and methylguanidinium, and the anionic acetate, phenolate, and alkanethiolates. In the present work, parameters for molecular ions in the context of the Drude polarizable force field are optimized and compared to results from the nonpolarizable additive CHARMM general force field (CGenFF). Electrostatic and Lennard-Jones parameters for the model compounds are developed in the context of the polarizable SWM4-NDP water model, with emphasis on assuring that the hydration free energies are consistent with previously reported parameters for atomic ions. The final parameters are shown to be in good agreement with the selected quantum mechanical (QM) and experimental target data. Analysis of the structure of water around the ions reveals substantial differences between the Drude and additive force fields indicating the important role of polarization in dictating the molecular details of aqueous solvation. The presented parameters represent the foundation for the charged functionalities in future generations of the Drude polarizable force field for biological macromolecules as well as for drug-like molecules.
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Affiliation(s)
- Fang-Yu Lin
- Department of Pharmaceutical Sciences, School of Pharmacy, University of Maryland, 20 Penn Street, Baltimore, MD 21201, USA
| | - Pedro E. M. Lopes
- Department of Pharmaceutical Sciences, School of Pharmacy, University of Maryland, 20 Penn Street, Baltimore, MD 21201, USA
| | - Edward Harder
- Department of Biochemistry and Molecular Biology, University of Chicago, Chicago, IL, 60637, USA
| | - Benoît Roux
- Department of Biochemistry and Molecular Biology, University of Chicago, Chicago, IL, 60637, USA
| | - Alexander D. MacKerell
- Department of Pharmaceutical Sciences, School of Pharmacy, University of Maryland, 20 Penn Street, Baltimore, MD 21201, USA
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8
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Zhang H, Yin C, Jiang Y, van der Spoel D. Force Field Benchmark of Amino Acids: I. Hydration and Diffusion in Different Water Models. J Chem Inf Model 2018; 58:1037-1052. [DOI: 10.1021/acs.jcim.8b00026] [Citation(s) in RCA: 61] [Impact Index Per Article: 10.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023]
Affiliation(s)
- Haiyang Zhang
- Department of Biological Science and Engineering, School of Chemistry and Biological Engineering, University of Science and Technology Beijing, Beijing 100083, China
| | - Chunhua Yin
- Department of Biological Science and Engineering, School of Chemistry and Biological Engineering, University of Science and Technology Beijing, Beijing 100083, China
| | - Yang Jiang
- Beijing Key Lab of Bioprocess, College of Life Science and Technology, Beijing University of Chemical Technology, Box 53, Beijing 100029, China
| | - David van der Spoel
- Uppsala Center for Computational Chemistry, Science for Life Laboratory, Department of Cell and Molecular Biology, Uppsala University, Husargatan 3, Box
596, SE-75124 Uppsala, Sweden
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9
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Giese TJ, York DM. A GPU-Accelerated Parameter Interpolation Thermodynamic Integration Free Energy Method. J Chem Theory Comput 2018; 14:1564-1582. [PMID: 29357243 PMCID: PMC5849537 DOI: 10.1021/acs.jctc.7b01175] [Citation(s) in RCA: 38] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022]
Abstract
There has been a resurgence of interest in free energy methods motivated by the performance enhancements offered by molecular dynamics (MD) software written for specialized hardware, such as graphics processing units (GPUs). In this work, we exploit the properties of a parameter-interpolated thermodynamic integration (PI-TI) method to connect states by their molecular mechanical (MM) parameter values. This pathway is shown to be better behaved for Mg2+ → Ca2+ transformations than traditional linear alchemical pathways (with and without soft-core potentials). The PI-TI method has the practical advantage that no modification of the MD code is required to propagate the dynamics, and unlike with linear alchemical mixing, only one electrostatic evaluation is needed (e.g., single call to particle-mesh Ewald) leading to better performance. In the case of AMBER, this enables all the performance benefits of GPU-acceleration to be realized, in addition to unlocking the full spectrum of features available within the MD software, such as Hamiltonian replica exchange (HREM). The TI derivative evaluation can be accomplished efficiently in a post-processing step by reanalyzing the statistically independent trajectory frames in parallel for high throughput. We also show how one can evaluate the particle mesh Ewald contribution to the TI derivative evaluation without needing to perform two reciprocal space calculations. We apply the PI-TI method with HREM on GPUs in AMBER to predict p Ka values in double stranded RNA molecules and make comparison with experiments. Convergence to under 0.25 units for these systems required 100 ns or more of sampling per window and coupling of windows with HREM. We find that MM charges derived from ab initio QM/MM fragment calculations improve the agreement between calculation and experimental results.
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Affiliation(s)
- Timothy J. Giese
- Laboratory for Biomolecular Simulation Research, Center for Integrative Proteomics Research, and Department of Chemistry and Chemical Biology, Rutgers University, Piscataway, New Jersey 08854-8087, United States
| | - Darrin M. York
- Laboratory for Biomolecular Simulation Research, Center for Integrative Proteomics Research, and Department of Chemistry and Chemical Biology, Rutgers University, Piscataway, New Jersey 08854-8087, United States
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10
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Qiao B, Skanthakumar S, Soderholm L. Comparative CHARMM and AMOEBA Simulations of Lanthanide Hydration Energetics and Experimental Aqueous-Solution Structures. J Chem Theory Comput 2018; 14:1781-1790. [DOI: 10.1021/acs.jctc.7b01018] [Citation(s) in RCA: 20] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/24/2022]
Affiliation(s)
- Baofu Qiao
- Chemical Sciences and Engineering Division, Argonne National Laboratory, Argonne, Illinois 60439, United States
| | - S. Skanthakumar
- Chemical Sciences and Engineering Division, Argonne National Laboratory, Argonne, Illinois 60439, United States
| | - L. Soderholm
- Chemical Sciences and Engineering Division, Argonne National Laboratory, Argonne, Illinois 60439, United States
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11
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Zhang H, Jiang Y, Yan H, Cui Z, Yin C. Comparative Assessment of Computational Methods for Free Energy Calculations of Ionic Hydration. J Chem Inf Model 2017; 57:2763-2775. [DOI: 10.1021/acs.jcim.7b00485] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- Haiyang Zhang
- Department
of Biological Science and Engineering, School of Chemistry and Biological
Engineering, University of Science and Technology Beijing, 100083 Beijing, China
| | - Yang Jiang
- Beijing
Key Lab of Bioprocess, College of Life Science and Technology, Beijing University of Chemical Technology, Box 53, 100029 Beijing, China
| | - Hai Yan
- Department
of Biological Science and Engineering, School of Chemistry and Biological
Engineering, University of Science and Technology Beijing, 100083 Beijing, China
| | - Ziheng Cui
- Beijing
Key Lab of Bioprocess, College of Life Science and Technology, Beijing University of Chemical Technology, Box 53, 100029 Beijing, China
| | - Chunhua Yin
- Department
of Biological Science and Engineering, School of Chemistry and Biological
Engineering, University of Science and Technology Beijing, 100083 Beijing, China
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12
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Duignan TT, Baer MD, Schenter GK, Mundy CJ. Electrostatic solvation free energies of charged hard spheres using molecular dynamics with density functional theory interactions. J Chem Phys 2017; 147:161716. [DOI: 10.1063/1.4994912] [Citation(s) in RCA: 40] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022] Open
Affiliation(s)
- Timothy T. Duignan
- Physical Science Division, Pacific Northwest National Laboratory, P.O. Box 999, Richland, Washington 99352, USA
| | - Marcel D. Baer
- Physical Science Division, Pacific Northwest National Laboratory, P.O. Box 999, Richland, Washington 99352, USA
| | - Gregory K. Schenter
- Physical Science Division, Pacific Northwest National Laboratory, P.O. Box 999, Richland, Washington 99352, USA
| | - Chistopher J. Mundy
- Department of Chemical Engineering, University of Washington, Seattle, Washington 98185, USA
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13
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Zhang H, Jiang Y, Yan H, Yin C, Tan T, van der Spoel D. Free-Energy Calculations of Ionic Hydration Consistent with the Experimental Hydration Free Energy of the Proton. J Phys Chem Lett 2017; 8:2705-2712. [PMID: 28561580 DOI: 10.1021/acs.jpclett.7b01125] [Citation(s) in RCA: 31] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 05/21/2023]
Abstract
Computational free-energy correction strategies and the choice of experimental proton hydration free energy, ΔGs*(H+), are analyzed to investigate the apparent controversy in experimental thermodynamics of ionic hydration. Without corrections, the hydration free-energy (ΔGhyd) calculations match experiments with ΔGs*(H+) = -1064 kJ/mol as reference. Using the Galvani surface potential the resulting (real) ΔGhyd are consistent with ΔGs*(H+) = -1098 kJ/mol. When applying, in an ad hoc manner, the discrete solvent correction, ΔGhyd matching the "consensus" ΔGs*(H+) of -1112 kJ/mol are obtained. This analysis rationalizes reports on ΔGhyd calculations for ions using different experimental references. For neutral amino acid side chains ΔGhyd are independent of the water model, whereas there are large differences in ΔGhyd due to the water model for charged species, suggesting that long-range ordering of water around ions yields an important contribution to the ΔGhyd. These differences are reduced significantly when applying consistent corrections, but to obtain the most accurate results it is recommended to use the water model belonging to the force field.
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Affiliation(s)
- Haiyang Zhang
- Department of Biological Science and Engineering, School of Chemistry and Biological Engineering, University of Science and Technology Beijing , 100083 Beijing, China
| | - Yang Jiang
- Beijing Key Lab of Bioprocess, College of Life Science and Technology, Beijing University of Chemical Technology , Box 53, 100029 Beijing, China
| | - Hai Yan
- Department of Biological Science and Engineering, School of Chemistry and Biological Engineering, University of Science and Technology Beijing , 100083 Beijing, China
| | - Chunhua Yin
- Department of Biological Science and Engineering, School of Chemistry and Biological Engineering, University of Science and Technology Beijing , 100083 Beijing, China
| | - Tianwei Tan
- Beijing Key Lab of Bioprocess, College of Life Science and Technology, Beijing University of Chemical Technology , Box 53, 100029 Beijing, China
| | - David van der Spoel
- Uppsala Center for Computational Chemistry, Science for Life Laboratory, Department of Cell and Molecular Biology, Uppsala University , Husargatan 3, Box 596, SE-75124 Uppsala, Sweden
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