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Klyshko E, Kim JSH, McGough L, Valeeva V, Lee E, Ranganathan R, Rauscher S. Functional protein dynamics in a crystal. Nat Commun 2024; 15:3244. [PMID: 38622111 PMCID: PMC11018856 DOI: 10.1038/s41467-024-47473-4] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/17/2023] [Accepted: 04/02/2024] [Indexed: 04/17/2024] Open
Abstract
Proteins are molecular machines and to understand how they work, we need to understand how they move. New pump-probe time-resolved X-ray diffraction methods open up ways to initiate and observe protein motions with atomistic detail in crystals on biologically relevant timescales. However, practical limitations of these experiments demands parallel development of effective molecular dynamics approaches to accelerate progress and extract meaning. Here, we establish robust and accurate methods for simulating dynamics in protein crystals, a nontrivial process requiring careful attention to equilibration, environmental composition, and choice of force fields. With more than seven milliseconds of sampling of a single chain, we identify critical factors controlling agreement between simulation and experiments and show that simulated motions recapitulate ligand-induced conformational changes. This work enables a virtuous cycle between simulation and experiments for visualizing and understanding the basic functional motions of proteins.
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Affiliation(s)
- Eugene Klyshko
- Department of Physics, University of Toronto, Toronto, ON, Canada
- Department of Chemical and Physical Sciences, University of Toronto Mississauga, Mississauga, ON, Canada
| | - Justin Sung-Ho Kim
- Department of Physics, University of Toronto, Toronto, ON, Canada
- Department of Chemical and Physical Sciences, University of Toronto Mississauga, Mississauga, ON, Canada
| | - Lauren McGough
- Department of Ecology and Evolution, University of Chicago, Chicago, IL, USA
| | - Victoria Valeeva
- Department of Chemical and Physical Sciences, University of Toronto Mississauga, Mississauga, ON, Canada
| | - Ethan Lee
- Department of Chemical and Physical Sciences, University of Toronto Mississauga, Mississauga, ON, Canada
- Department of Chemistry, University of Toronto, Toronto, ON, Canada
| | - Rama Ranganathan
- Center for Physics of Evolving Systems and Department of Biochemistry and Molecular Biology, University of Chicago, Chicago, IL, USA
- Pritzker School of Molecular Engineering, University of Chicago, Chicago, IL, USA
| | - Sarah Rauscher
- Department of Physics, University of Toronto, Toronto, ON, Canada.
- Department of Chemical and Physical Sciences, University of Toronto Mississauga, Mississauga, ON, Canada.
- Department of Chemistry, University of Toronto, Toronto, ON, Canada.
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2
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Klyshko E, Sung-Ho Kim J, McGough L, Valeeva V, Lee E, Ranganathan R, Rauscher S. Functional Protein Dynamics in a Crystal. BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2024:2023.07.06.548023. [PMID: 37461732 PMCID: PMC10350071 DOI: 10.1101/2023.07.06.548023] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Indexed: 07/27/2023]
Abstract
Proteins are molecular machines and to understand how they work, we need to understand how they move. New pump-probe time-resolved X-ray diffraction methods open up ways to initiate and observe protein motions with atomistic detail in crystals on biologically relevant timescales. However, practical limitations of these experiments demands parallel development of effective molecular dynamics approaches to accelerate progress and extract meaning. Here, we establish robust and accurate methods for simulating dynamics in protein crystals, a nontrivial process requiring careful attention to equilibration, environmental composition, and choice of force fields. With more than seven milliseconds of sampling of a single chain, we identify critical factors controlling agreement between simulation and experiments and show that simulated motions recapitulate ligand-induced conformational changes. This work enables a virtuous cycle between simulation and experiments for visualizing and understanding the basic functional motions of proteins.
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Affiliation(s)
- Eugene Klyshko
- Department of Physics, University of Toronto, Toronto, ON, Canada
- Department of Chemical and Physical Sciences, University of Toronto Mississauga, Mississauga, ON, Canada
| | - Justin Sung-Ho Kim
- Department of Physics, University of Toronto, Toronto, ON, Canada
- Department of Chemical and Physical Sciences, University of Toronto Mississauga, Mississauga, ON, Canada
| | - Lauren McGough
- Department of Ecology and Evolution, University of Chicago, Chicago, IL, USA
| | - Victoria Valeeva
- Department of Chemical and Physical Sciences, University of Toronto Mississauga, Mississauga, ON, Canada
| | - Ethan Lee
- Department of Chemical and Physical Sciences, University of Toronto Mississauga, Mississauga, ON, Canada
- Department of Chemistry, University of Toronto, Toronto, ON, Canada
| | - Rama Ranganathan
- Center for Physics of Evolving Systems and Department of Biochemistry and Molecular Biology, University of Chicago, Chicago, IL, USA
- Pritzker School of Molecular Engineering, University of Chicago, Chicago, IL, USA
| | - Sarah Rauscher
- Department of Physics, University of Toronto, Toronto, ON, Canada
- Department of Chemical and Physical Sciences, University of Toronto Mississauga, Mississauga, ON, Canada
- Department of Chemistry, University of Toronto, Toronto, ON, Canada
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3
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Biswal S, Agmon N. Collagen Structured Hydration. Biomolecules 2023; 13:1744. [PMID: 38136615 PMCID: PMC10742079 DOI: 10.3390/biom13121744] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/03/2023] [Revised: 11/17/2023] [Accepted: 11/20/2023] [Indexed: 12/24/2023] Open
Abstract
Collagen is a triple-helical protein unique to the extracellular matrix, conferring rigidity and stability to tissues such as bone and tendon. For the [(PPG)10]3 collagen-mimetic peptide at room temperature, our molecular dynamics simulations show that these properties result in a remarkably ordered first hydration layer of water molecules hydrogen bonded to the backbone carbonyl (bb-CO) oxygen atoms. This originates from the following observations. The radius of gyration attests that the PPG triplets are organized along a straight line, so that all triplets (excepting the ends) are equivalent. The solvent-accessible surface area (SASA) for the bb-CO oxygens shows a repetitive regularity for every triplet. This leads to water occupancy of the bb-CO sites following a similar regularity. In the crystal-phase X-ray data, as well as in our 100 K simulations, we observe a 0-2-1 water occupancy in the P-P-G triplet. Surprisingly, a similar (0-1.7-1) regularity is maintained in the liquid phase, in spite of the sub-nsec water exchange rates, because the bb-CO sites rarely remain vacant. The manifested ordered first-shell water molecules are expected to produce a cylindrical electrostatic potential around the peptide, to be investigated in future work.
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Affiliation(s)
| | - Noam Agmon
- The Fritz Haber Research Center, Institute of Chemistry, The Hebrew University of Jerusalem, Jerusalem 9190401, Israel;
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4
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Klyshko E, Kim JSH, Rauscher S. LAWS: Local alignment for water sites-Tracking ordered water in simulations. Biophys J 2023; 122:2871-2883. [PMID: 36116009 PMCID: PMC10397812 DOI: 10.1016/j.bpj.2022.09.012] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/16/2022] [Revised: 09/01/2022] [Accepted: 09/13/2022] [Indexed: 11/02/2022] Open
Abstract
Accurate modeling of protein-water interactions in molecular dynamics (MD) simulations is important for understanding the molecular basis of protein function. Data from x-ray crystallography can be useful in assessing the accuracy of MD simulations, in particular, the locations of crystallographic water sites (CWS) coordinated by the protein. Such a comparison requires special methodological considerations that take into account the dynamic nature of proteins. However, existing methods for analyzing CWS in MD simulations rely on global alignment of the protein onto the crystal structure, which introduces substantial errors in the case of significant structural deviations. Here, we propose a method called local alignment for water sites (LAWS), which is based on multilateration-an algorithm widely used in GPS tracking. LAWS considers the contacts formed by CWS and protein atoms in the crystal structure and uses these interaction distances to track CWS in a simulation. We apply our method to simulations of a protein crystal and to simulations of the same protein in solution. Compared with existing methods, LAWS defines CWS characterized by more prominent water density peaks and a less-perturbed protein environment. In the crystal, we find that all high-confidence crystallographic waters are preserved. Using LAWS, we demonstrate the importance of crystal packing for the stability of CWS in the unit cell. Simulations of the protein in solution and in the crystal share a common set of preserved CWS that are located in pockets and coordinated by residues of the same domain, which suggests that the LAWS algorithm will also be useful in studying ordered waters and water networks in general.
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Affiliation(s)
- Eugene Klyshko
- Department of Physics, University of Toronto, Toronto, Ontario, Canada; Department of Chemical and Physical Sciences, University of Toronto Mississauga, Mississauga, Ontario, Canada
| | - Justin Sung-Ho Kim
- Department of Physics, University of Toronto, Toronto, Ontario, Canada; Department of Chemical and Physical Sciences, University of Toronto Mississauga, Mississauga, Ontario, Canada
| | - Sarah Rauscher
- Department of Physics, University of Toronto, Toronto, Ontario, Canada; Department of Chemical and Physical Sciences, University of Toronto Mississauga, Mississauga, Ontario, Canada; Department of Chemistry, University of Toronto, Toronto, Ontario, Canada.
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5
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Doyle M, Bhowmick A, Wych DC, Lassalle L, Simon PS, Holton J, Sauter NK, Yachandra VK, Kern JF, Yano J, Wall ME. Water Networks in Photosystem II Using Crystalline Molecular Dynamics Simulations and Room-Temperature XFEL Serial Crystallography. J Am Chem Soc 2023; 145:14621-14635. [PMID: 37369071 PMCID: PMC10347547 DOI: 10.1021/jacs.3c01412] [Citation(s) in RCA: 13] [Impact Index Per Article: 13.0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/07/2023] [Indexed: 06/29/2023]
Abstract
Structural dynamics of water and its hydrogen-bonding networks play an important role in enzyme function via the transport of protons, ions, and substrates. To gain insights into these mechanisms in the water oxidation reaction in Photosystem II (PS II), we have performed crystalline molecular dynamics (MD) simulations of the dark-stable S1 state. Our MD model consists of a full unit cell with 8 PS II monomers in explicit solvent (861 894 atoms), enabling us to compute the simulated crystalline electron density and to compare it directly with the experimental density from serial femtosecond X-ray crystallography under physiological temperature collected at X-ray free electron lasers (XFELs). The MD density reproduced the experimental density and water positions with high fidelity. The detailed dynamics in the simulations provided insights into the mobility of water molecules in the channels beyond what can be interpreted from experimental B-factors and electron densities alone. In particular, the simulations revealed fast, coordinated exchange of waters at sites where the density is strong, and water transport across the bottleneck region of the channels where the density is weak. By computing MD hydrogen and oxygen maps separately, we developed a novel Map-based Acceptor-Donor Identification (MADI) technique that yields information which helps to infer hydrogen-bond directionality and strength. The MADI analysis revealed a series of hydrogen-bond wires emanating from the Mn cluster through the Cl1 and O4 channels; such wires might provide pathways for proton transfer during the reaction cycle of PS II. Our simulations provide an atomistic picture of the dynamics of water and hydrogen-bonding networks in PS II, with implications for the specific role of each channel in the water oxidation reaction.
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Affiliation(s)
- Margaret
D. Doyle
- Molecular
Biophysics and Integrated Bioimaging Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, United States
| | - Asmit Bhowmick
- Molecular
Biophysics and Integrated Bioimaging Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, United States
| | - David C. Wych
- Computer,
Computational and Statistical Sciences Division, Los Alamos National Laboratory, Los Alamos, New Mexico 87545, United States
- Center
for Non-linear Studies, Los Alamos National
Laboratory, Los Alamos, New Mexico 87545, United States
| | - Louise Lassalle
- Molecular
Biophysics and Integrated Bioimaging Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, United States
| | - Philipp S. Simon
- Molecular
Biophysics and Integrated Bioimaging Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, United States
| | - James Holton
- Molecular
Biophysics and Integrated Bioimaging Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, United States
- Department
of Biochemistry and Biophysics, University
of California, San Francisco, San
Francisco, California 94158, United States
- SSRL, SLAC National Accelerator Laboratory, Menlo Park, California 94025, United States
| | - Nicholas K. Sauter
- Molecular
Biophysics and Integrated Bioimaging Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, United States
| | - Vittal K. Yachandra
- Molecular
Biophysics and Integrated Bioimaging Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, United States
| | - Jan F. Kern
- Molecular
Biophysics and Integrated Bioimaging Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, United States
| | - Junko Yano
- Molecular
Biophysics and Integrated Bioimaging Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, United States
| | - Michael E. Wall
- Computer,
Computational and Statistical Sciences Division, Los Alamos National Laboratory, Los Alamos, New Mexico 87545, United States
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Liu N, Mikhailovskii O, Skrynnikov NR, Xue Y. Simulating diffraction photographs based on molecular dynamics trajectories of a protein crystal: a new option to examine structure-solving strategies in protein crystallography. IUCRJ 2023; 10:16-26. [PMID: 36598499 PMCID: PMC9812212 DOI: 10.1107/s2052252522011198] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 06/06/2022] [Accepted: 11/21/2022] [Indexed: 06/17/2023]
Abstract
A molecular dynamics (MD)-based pipeline has been designed and implemented to emulate the entire process of collecting diffraction photographs and calculating crystallographic structures of proteins from them. Using a structure of lysozyme solved in-house, a supercell comprising 125 (5 × 5 × 5) crystal unit cells containing a total of 1000 protein molecules and explicit interstitial solvent was constructed. For this system, two 300 ns MD trajectories at 298 and 250 K were recorded. A series of snapshots from these trajectories were then used to simulate a fully realistic set of diffraction photographs, which were further fed into the standard pipeline for structure determination. The resulting structures show very good agreement with the underlying MD model not only in terms of coordinates but also in terms of B factors; they are also consistent with the original experimental structure. The developed methodology should find a range of applications, such as optimizing refinement protocols to solve crystal structures and extracting dynamics information from diffraction data or diffuse scattering.
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Affiliation(s)
- Ning Liu
- School of Life Sciences, Tsinghua University, Beijing 100084, People’s Republic of China
| | - Oleg Mikhailovskii
- Laboratory of Biomolecular NMR, St Petersburg State University, St Petersburg, Russian Federation
- Department of Chemistry, Purdue University, West Lafayette, IN 47907, USA
| | - Nikolai R. Skrynnikov
- Laboratory of Biomolecular NMR, St Petersburg State University, St Petersburg, Russian Federation
- Department of Chemistry, Purdue University, West Lafayette, IN 47907, USA
| | - Yi Xue
- School of Life Sciences, Tsinghua University, Beijing 100084, People’s Republic of China
- Beijing Advanced Innovation Center for Structural Biology, Tsinghua University, Beijing 100084, People’s Republic of China
- Tsinghua University–Peking University Joint Center for Life Sciences, Tsinghua University, Beijing 100084, People’s Republic of China
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7
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Mueller NPF, Carloni P, Alfonso-Prieto M. Molecular determinants of acrylamide neurotoxicity through covalent docking. Front Pharmacol 2023; 14:1125871. [PMID: 36937867 PMCID: PMC10018202 DOI: 10.3389/fphar.2023.1125871] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/16/2022] [Accepted: 02/17/2023] [Indexed: 03/06/2023] Open
Abstract
Acrylamide (ACR) is formed during food processing by Maillard reaction between sugars and proteins at high temperatures. It is also used in many industries, from water waste treatment to manufacture of paper, fabrics, dyes and cosmetics. Unfortunately, cumulative exposure to acrylamide, either from diet or at the workplace, may result in neurotoxicity. Such adverse effects arise from covalent adducts formed between acrylamide and cysteine residues of several neuronal proteins via a Michael addition reaction. The molecular determinants of acrylamide reactivity and its impact on protein function are not completely understood. Here we have compiled a list of acrylamide protein targets reported so far in the literature in connection with neurotoxicity and performed a systematic covalent docking study. Our results indicate that acrylamide binding to cysteine is favored in the presence of nearby positively charged amino acids, such as lysines and arginines. For proteins with more than one reactive Cys, docking scores were able to discriminate between the primary ACR modification site and secondary sites modified only at high ACR concentrations. Therefore, docking scores emerge as a potential filter to predict Cys reactivity against acrylamide. Inspection of the ACR-protein complex structures provides insights into the putative functional consequences of ACR modification, especially for non-enzyme proteins. Based on our study, covalent docking is a promising computational tool to predict other potential protein targets mediating acrylamide neurotoxicity.
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Affiliation(s)
- Nicolas Pierre Friedrich Mueller
- Institute for Advanced Simulations IAS-5, Institute of Neuroscience and Medicine INM-9, Computational Biomedicine, Forschungszentrum Jülich, Jülich, Germany
- Faculty of Mathematics and Natural Sciences, Heinrich Heine University Düsseldorf, Düsseldorf, Germany
| | - Paolo Carloni
- Institute for Advanced Simulations IAS-5, Institute of Neuroscience and Medicine INM-9, Computational Biomedicine, Forschungszentrum Jülich, Jülich, Germany
- Department of Physics, RWTH Aachen University, Aachen, Germany
| | - Mercedes Alfonso-Prieto
- Institute for Advanced Simulations IAS-5, Institute of Neuroscience and Medicine INM-9, Computational Biomedicine, Forschungszentrum Jülich, Jülich, Germany
- Cécile and Oskar Vogt Institute for Brain Research, Medical Faculty, University Hospital Düsseldorf, Heinrich Heine University Düsseldorf, Düsseldorf, Germany
- *Correspondence: Mercedes Alfonso-Prieto,
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8
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Ekberg V, Samways ML, Misini Ignjatović M, Essex JW, Ryde U. Comparison of Grand Canonical and Conventional Molecular Dynamics Simulation Methods for Protein-Bound Water Networks. ACS PHYSICAL CHEMISTRY AU 2022; 2:247-259. [PMID: 35637786 PMCID: PMC9136951 DOI: 10.1021/acsphyschemau.1c00052] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 12/17/2021] [Revised: 01/28/2022] [Accepted: 01/28/2022] [Indexed: 11/28/2022]
Abstract
![]()
Water molecules play
important roles in all biochemical processes.
Therefore, it is of key importance to obtain information of the structure,
dynamics, and thermodynamics of water molecules around proteins. Numerous
computational methods have been suggested with this aim. In this study,
we compare the performance of conventional and grand-canonical Monte
Carlo (GCMC) molecular dynamics (MD) simulations to sample the water
structure, as well GCMC and grid-based inhomogeneous solvation theory
(GIST) to describe the energetics of the water network. They are evaluated
on two proteins: the buried ligand-binding site of a ferritin dimer
and the solvent-exposed binding site of galectin-3. We show that GCMC/MD
simulations significantly speed up the sampling and equilibration
of water molecules in the buried binding site, thereby making the
results more similar for simulations started from different states.
Both GCMC/MD and conventional MD reproduce crystal-water molecules
reasonably for the buried binding site. GIST analyses are normally
based on restrained MD simulations. This improves the precision of
the calculated energies, but the restraints also significantly affect
both absolute and relative energies. Solvation free energies for individual
water molecules calculated with and without restraints show a good
correlation, but with large quantitative differences. Finally, we
note that the solvation free energies calculated with GIST are ∼5
times larger than those estimated by GCMC owing to differences in
the reference state.
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Affiliation(s)
- Vilhelm Ekberg
- Department of Theoretical Chemistry, Lund University, Chemical Centre, P.O. Box 124, Lund SE-221 00, Sweden
| | - Marley L. Samways
- School of Chemistry, University of Southampton, Southampton SO17 1BJ, U.K
| | - Majda Misini Ignjatović
- Department of Theoretical Chemistry, Lund University, Chemical Centre, P.O. Box 124, Lund SE-221 00, Sweden
| | - Jonathan W. Essex
- School of Chemistry, University of Southampton, Southampton SO17 1BJ, U.K
| | - Ulf Ryde
- Department of Theoretical Chemistry, Lund University, Chemical Centre, P.O. Box 124, Lund SE-221 00, Sweden
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Núñez-Franco R, Peccati F, Jiménez-Osés G. A Computational Perspective on Molecular Recognition by Galectins. Curr Med Chem 2021; 29:1219-1231. [PMID: 34348610 DOI: 10.2174/0929867328666210804093058] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/07/2021] [Revised: 06/17/2021] [Accepted: 06/28/2021] [Indexed: 11/22/2022]
Abstract
This article presents an overview of recent computational studies dedicated to the analysis of binding between galectins and small-molecule ligands. We first present a summary of the most popular simulation techniques adopted for calculating binding poses and binding energies, and then discuss relevant examples reported in the literature for the three main classes of galectins (dimeric, tandem and chimera). We show that simulation of galectin-ligand interactions is a mature field which has proven invaluable for completing and unraveling experimental observations. Future perspectives to further improve the accuracy and cost-effectiveness of existing computational approaches will involve the development of new schemes to account for solvation and entropy effects, which represent the main current limitations to the accuracy of computational results.
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Affiliation(s)
- Reyes Núñez-Franco
- CIC bioGUNE, Basque Research and Technology Alliance (BRTA), Bizkaia Technology Park, Building 800, 48160 Derio. Spain
| | - Francesca Peccati
- CIC bioGUNE, Basque Research and Technology Alliance (BRTA), Bizkaia Technology Park, Building 800, 48160 Derio. Spain
| | - Gonzalo Jiménez-Osés
- CIC bioGUNE, Basque Research and Technology Alliance (BRTA), Bizkaia Technology Park, Building 800, 48160 Derio. Spain
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10
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Caldararu O, Ekberg V, Logan DT, Oksanen E, Ryde U. Exploring ligand dynamics in protein crystal structures with ensemble refinement. Acta Crystallogr D Struct Biol 2021; 77:1099-1115. [PMID: 34342282 PMCID: PMC8329865 DOI: 10.1107/s2059798321006513] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/17/2021] [Accepted: 06/21/2021] [Indexed: 11/10/2022] Open
Abstract
Understanding the dynamics of ligands bound to proteins is an important task in medicinal chemistry and drug design. However, the dominant technique for determining protein-ligand structures, X-ray crystallography, does not fully account for dynamics and cannot accurately describe the movements of ligands in protein binding sites. In this article, an alternative method, ensemble refinement, is used on six protein-ligand complexes with the aim of understanding the conformational diversity of ligands in protein crystal structures. The results show that ensemble refinement sometimes indicates that the flexibility of parts of the ligand and some protein side chains is larger than that which can be described by a single conformation and atomic displacement parameters. However, since the electron-density maps are comparable and Rfree values are slightly increased, the original crystal structure is still a better model from a statistical point of view. On the other hand, it is shown that molecular-dynamics simulations and automatic generation of alternative conformations in crystallographic refinement confirm that the flexibility of these groups is larger than is observed in standard refinement. Moreover, the flexible groups in ensemble refinement coincide with groups that give high atomic displacement parameters or non-unity occupancy if optimized in standard refinement. Therefore, the conformational diversity indicated by ensemble refinement seems to be qualitatively correct, indicating that ensemble refinement can be an important complement to standard crystallographic refinement as a tool to discover which parts of crystal structures may show extensive flexibility and therefore are poorly described by a single conformation. However, the diversity of the ensembles is often exaggerated (probably partly owing to the rather poor force field employed) and the ensembles should not be trusted in detail.
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Affiliation(s)
- Octav Caldararu
- Department of Theoretical Chemistry, Lund University, Chemical Centre, PO Box 124, SE-221 00 Lund, Sweden
| | - Vilhelm Ekberg
- Department of Theoretical Chemistry, Lund University, Chemical Centre, PO Box 124, SE-221 00 Lund, Sweden
| | - Derek T. Logan
- Biochemistry and Structural Biology, Centre for Molecular Protein Science, Department of Chemistry, Lund University, Chemical Centre, PO Box 124, SE-221 00 Lund, Sweden
| | - Esko Oksanen
- European Spallation Source Consortium ESS ERIC, PO Box 176, SE-221 00 Lund, Sweden
| | - Ulf Ryde
- Department of Theoretical Chemistry, Lund University, Chemical Centre, PO Box 124, SE-221 00 Lund, Sweden
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