1
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Kaiser S, Yue Z, Peng Y, Nguyen TD, Chen S, Teng D, Voth GA. Molecular Dynamics Simulation of Complex Reactivity with the Rapid Approach for Proton Transport and Other Reactions (RAPTOR) Software Package. J Phys Chem B 2024; 128:4959-4974. [PMID: 38742764 PMCID: PMC11129700 DOI: 10.1021/acs.jpcb.4c01987] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/26/2024] [Revised: 05/05/2024] [Accepted: 05/06/2024] [Indexed: 05/16/2024]
Abstract
Simulating chemically reactive phenomena such as proton transport on nanosecond to microsecond and beyond time scales is a challenging task. Ab initio methods are unable to currently access these time scales routinely, and traditional molecular dynamics methods feature fixed bonding arrangements that cannot account for changes in the system's bonding topology. The Multiscale Reactive Molecular Dynamics (MS-RMD) method, as implemented in the Rapid Approach for Proton Transport and Other Reactions (RAPTOR) software package for the LAMMPS molecular dynamics code, offers a method to routinely sample longer time scale reactive simulation data with statistical precision. RAPTOR may also be interfaced with enhanced sampling methods to drive simulations toward the analysis of reactive rare events, and a number of collective variables (CVs) have been developed to facilitate this. Key advances to this methodology, including GPU acceleration efforts and novel CVs to model water wire formation are reviewed, along with recent applications of the method which demonstrate its versatility and robustness.
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Affiliation(s)
- Scott Kaiser
- Department
of Chemistry, Chicago Center for Theoretical Chemistry, James Franck
Institute, and Institute for Biophysical Dynamics, The University of Chicago, Chicago, Illinois 60637, United States
| | - Zhi Yue
- Department
of Chemistry, Chicago Center for Theoretical Chemistry, James Franck
Institute, and Institute for Biophysical Dynamics, The University of Chicago, Chicago, Illinois 60637, United States
| | - Yuxing Peng
- NVIDIA
Corporation, Santa
Clara, California 95051, United States
| | - Trung Dac Nguyen
- Research
Computing Center, The University of Chicago, Chicago, Illinois 60637, United States
| | - Sijia Chen
- Department
of Chemistry, Chicago Center for Theoretical Chemistry, James Franck
Institute, and Institute for Biophysical Dynamics, The University of Chicago, Chicago, Illinois 60637, United States
| | - Da Teng
- Department
of Chemistry, Chicago Center for Theoretical Chemistry, James Franck
Institute, and Institute for Biophysical Dynamics, The University of Chicago, Chicago, Illinois 60637, United States
| | - Gregory A. Voth
- Department
of Chemistry, Chicago Center for Theoretical Chemistry, James Franck
Institute, and Institute for Biophysical Dynamics, The University of Chicago, Chicago, Illinois 60637, United States
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2
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Costa GJ, Liang R. Understanding the Multifaceted Mechanism of Compound I Formation in Unspecific Peroxygenases through Multiscale Simulations. J Phys Chem B 2023; 127:8809-8824. [PMID: 37796883 DOI: 10.1021/acs.jpcb.3c04589] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/07/2023]
Abstract
Unspecific peroxygenases (UPOs) can selectively oxyfunctionalize unactivated hydrocarbons by using peroxides under mild conditions. They circumvent the oxygen dilemma faced by cytochrome P450s and exhibit greater stability than the latter. As such, they hold great potential for industrial applications. A thorough understanding of their catalysis is needed to improve their catalytic performance. However, it remains elusive how UPOs effectively convert peroxide to Compound I (CpdI), the principal oxidizing intermediate in the catalytic cycle. Previous computational studies of this process primarily focused on heme peroxidases and P450s, which have significant differences in the active site from UPOs. Additionally, the roles of peroxide unbinding in the kinetics of CpdI formation, which is essential for interpreting existing experiments, have been understudied. Moreover, there has been a lack of free energy characterizations with explicit sampling of protein and hydration dynamics, which is critical for understanding the thermodynamics of the proton transport (PT) events involved in CpdI formation. To bridge these gaps, we employed multiscale simulations to comprehensively characterize the CpdI formation in wild-type UPO from Agrocybe aegerita (AaeUPO). Extensive free energy and potential energy calculations were performed in a quantum mechanics/molecular mechanics setting. Our results indicate that substrate-binding dehydrates the active site, impeding the PT from H2O2 to a nearby catalytic base (Glu196). Furthermore, the PT is coupled with considerable hydrogen bond network rearrangements near the active site, facilitating subsequent O-O bond cleavage. Finally, large unbinding free energy barriers kinetically stabilize H2O2 at the active site. These findings reveal a delicate balance among PT, hydration dynamics, hydrogen bond rearrangement, and cosubstrate unbinding, which collectively enable efficient CpdI formation. Our simulation results are consistent with kinetic measurements and offer new insights into the CpdI formation mechanism at atomic-level details, which can potentially aid the design of next-generation biocatalysts for sustainable chemical transformations of feedstocks.
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Affiliation(s)
- Gustavo J Costa
- Department of Chemistry and Biochemistry, Texas Tech University, Lubbock, Texas 79409, United States
| | - Ruibin Liang
- Department of Chemistry and Biochemistry, Texas Tech University, Lubbock, Texas 79409, United States
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3
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Kratochvil HT, Watkins LC, Mravic M, Thomaston JL, Nicoludis JM, Somberg NH, Liu L, Hong M, Voth GA, DeGrado WF. Transient water wires mediate selective proton transport in designed channel proteins. Nat Chem 2023; 15:1012-1021. [PMID: 37308712 PMCID: PMC10475958 DOI: 10.1038/s41557-023-01210-4] [Citation(s) in RCA: 12] [Impact Index Per Article: 12.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/19/2022] [Accepted: 04/19/2023] [Indexed: 06/14/2023]
Abstract
Selective proton transport through proteins is essential for forming and using proton gradients in cells. Protons are conducted along hydrogen-bonded 'wires' of water molecules and polar side chains, which, somewhat surprisingly, are often interrupted by dry apolar stretches in the conduction pathways, inferred from static protein structures. Here we hypothesize that protons are conducted through such dry spots by forming transient water wires, often highly correlated with the presence of the excess protons in the water wire. To test this hypothesis, we performed molecular dynamics simulations to design transmembrane channels with stable water pockets interspersed by apolar segments capable of forming flickering water wires. The minimalist designed channels conduct protons at rates similar to viral proton channels, and they are at least 106-fold more selective for H+ over Na+. These studies inform the mechanisms of biological proton conduction and the principles for engineering proton-conductive materials.
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Affiliation(s)
- Huong T Kratochvil
- Department of Pharmaceutical Chemistry, University of California-San Francisco, San Francisco, CA, USA.
- Department of Chemistry, University of North Carolina at Chapel Hill, Chapel Hill, NC, USA.
| | - Laura C Watkins
- Department of Chemistry, Chicago Center for Theoretical Chemistry, Institute for Biophysical Dynamics and James Franck Institute, The University of Chicago, Chicago, IL, USA
- Kemper Insurance, Chicago, IL, USA
| | - Marco Mravic
- Department of Pharmaceutical Chemistry, University of California-San Francisco, San Francisco, CA, USA
- Department of Integrative Structural and Computational Biology Scripps Research Institute, La Jolla, CA, USA
| | - Jessica L Thomaston
- Department of Pharmaceutical Chemistry, University of California-San Francisco, San Francisco, CA, USA
| | - John M Nicoludis
- Department of Pharmaceutical Chemistry, University of California-San Francisco, San Francisco, CA, USA
- Genentech, San Francisco, CA, USA
| | - Noah H Somberg
- Department of Chemistry, Massachusetts Institute of Technology, Cambridge, MA, USA
| | | | - Mei Hong
- Department of Chemistry, Massachusetts Institute of Technology, Cambridge, MA, USA
| | - Gregory A Voth
- Department of Chemistry, Chicago Center for Theoretical Chemistry, Institute for Biophysical Dynamics and James Franck Institute, The University of Chicago, Chicago, IL, USA.
| | - William F DeGrado
- Department of Pharmaceutical Chemistry, University of California-San Francisco, San Francisco, CA, USA.
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4
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Raman AS, Selloni A. Modeling the Solvation and Acidity of Carboxylic Acids Using an Ab Initio Deep Neural Network Potential. J Phys Chem A 2022; 126:7283-7290. [PMID: 36194268 DOI: 10.1021/acs.jpca.2c06252] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Formic and acetic acid constitute the simplest of carboxylic acids, yet they exhibit fascinating chemistry in the condensed phase such as proton transfer and dimerization. The go-to method of choice for modeling these rare events have been accurate but expensive ab initio molecular dynamics simulations. In this study, we present a deep neural network potential trained using accurate ab initio data that can be used in tandem with enhanced-sampling methods to perform an efficient exploration of the free-energy surface of aqueous solutions of weak carboxylic acids. In particular, we show that our model captures proton dissociation and provides a good estimate of the pKa, as well as the dimerization of formic and acetic acid. This provides a suitable starting point for applications in different research areas where computational efficiency coupled with the accuracy of ab initio methods is required.
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Affiliation(s)
- Abhinav S Raman
- Department of Chemistry, Princeton University, Princeton, New Jersey08544, United States
| | - Annabella Selloni
- Department of Chemistry, Princeton University, Princeton, New Jersey08544, United States
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5
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Zuchniarz J, Liu Y, Li C, Voth GA. Accurate p Ka Calculations in Proteins with Reactive Molecular Dynamics Provide Physical Insight Into the Electrostatic Origins of Their Values. J Phys Chem B 2022; 126:7321-7330. [PMID: 36106487 PMCID: PMC9528908 DOI: 10.1021/acs.jpcb.2c04899] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/11/2022] [Revised: 08/28/2022] [Indexed: 11/29/2022]
Abstract
Classical molecular dynamics simulations are a versatile tool in the study of biomolecular systems, but they usually rely on a fixed bonding topology, precluding the explicit simulation of chemical reactivity. Certain modifications can permit the modeling of reactions. One such method, multiscale reactive molecular dynamics, makes use of a linear combination approach to describe condensed-phase free energy surfaces of reactive processes of biological interest. Before these simulations can be performed, models of the reactive moieties must first be parametrized using electronic structure data. A recent study demonstrated that gas-phase electronic structure data can be used to derive parameters for glutamate and lysine which reproduce experimental pKa values in both bulk water and the staphylococcal nuclease protein with remarkable accuracy and transferability between the water and protein environments. In this work, we first present a new model for aspartate derived in similar fashion and demonstrate that it too produces accurate pKa values in both bulk and protein contexts. We also describe a modification to the prior methodology, involving refitting some of the classical force field parameters to density functional theory calculations, which improves the transferability of the existing glutamate model. Finally and most importantly, this reactive molecular dynamics approach, based on rigorous statistical mechanics, allows one to specifically analyze the fundamental physical causes for the marked pKa shift of both aspartate and glutamate between bulk water and protein and also to demonstrate that local steric and electrostatic effects largely explain the observed differences.
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Affiliation(s)
- Joshua Zuchniarz
- Department of Chemistry, Chicago Center
for Theoretical Chemistry, James Franck Institute, and Institute for
Biophysical Dynamics, The University of
Chicago, Chicago, Illinois 60637, United States
| | - Yu Liu
- Department of Chemistry, Chicago Center
for Theoretical Chemistry, James Franck Institute, and Institute for
Biophysical Dynamics, The University of
Chicago, Chicago, Illinois 60637, United States
| | - Chenghan Li
- Department of Chemistry, Chicago Center
for Theoretical Chemistry, James Franck Institute, and Institute for
Biophysical Dynamics, The University of
Chicago, Chicago, Illinois 60637, United States
| | - Gregory A. Voth
- Department of Chemistry, Chicago Center
for Theoretical Chemistry, James Franck Institute, and Institute for
Biophysical Dynamics, The University of
Chicago, Chicago, Illinois 60637, United States
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6
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Kollias L, Zhang D, Allec SI, Nguyen MT, Lee MS, Cantu DC, Rousseau R, Glezakou VA. Advanced Theory and Simulation to Guide the Development of CO 2 Capture Solvents. ACS OMEGA 2022; 7:12453-12466. [PMID: 35465123 PMCID: PMC9022203 DOI: 10.1021/acsomega.1c07398] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 12/31/2021] [Accepted: 03/03/2022] [Indexed: 06/14/2023]
Abstract
Increasing atmospheric concentrations of greenhouse gases due to industrial activity have led to concerning levels of global warming. Reducing carbon dioxide (CO2) emissions, one of the main contributors to the greenhouse effect, is key to mitigating further warming and its negative effects on the planet. CO2 capture solvent systems are currently the only available technology deployable at scales commensurate with industrial processes. Nonetheless, designing these solvents for a given application is a daunting task requiring the optimization of both thermodynamic and transport properties. Here, we discuss the use of atomic scale modeling for computing reaction energetics and transport properties of these chemically complex solvents. Theoretical studies have shown that in many cases, one is dealing with a rich ensemble of chemical species in a coupled equilibrium that is often difficult to characterize and quantify by experiment alone. As a result, solvent design is a balancing act between multiple parameters which have optimal zones of effectiveness depending on the operating conditions of the application. Simulation of reaction mechanisms has shown that CO2 binding and proton transfer reactions create chemical equilibrium between multiple species and that the agglomeration of resulting ions and zwitterions can have profound effects on bulk solvent properties such as viscosity. This is balanced against the solvent systems needing to perform different functions (e.g., CO2 uptake and release) depending on the thermodynamic conditions (e.g., temperature and pressure swings). The latter constraint imposes a "Goldilocks" range of effective parameters, such as binding enthalpy and pK a, which need to be tuned at the molecular level. The resulting picture is that solvent development requires an integrated approach where theory and simulation can provide the necessary ingredients to balance competing factors.
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Affiliation(s)
- Loukas Kollias
- Basic
& Applied Molecular Foundations, Physical and Computational Sciences
Directorate, Pacific Northwest National
Laboratory, Richland, Washington 99352, United States
| | - Difan Zhang
- Basic
& Applied Molecular Foundations, Physical and Computational Sciences
Directorate, Pacific Northwest National
Laboratory, Richland, Washington 99352, United States
| | - Sarah I. Allec
- Basic
& Applied Molecular Foundations, Physical and Computational Sciences
Directorate, Pacific Northwest National
Laboratory, Richland, Washington 99352, United States
| | - Manh-Thuong Nguyen
- Basic
& Applied Molecular Foundations, Physical and Computational Sciences
Directorate, Pacific Northwest National
Laboratory, Richland, Washington 99352, United States
| | - Mal-Soon Lee
- Basic
& Applied Molecular Foundations, Physical and Computational Sciences
Directorate, Pacific Northwest National
Laboratory, Richland, Washington 99352, United States
| | - David C. Cantu
- Department
of Chemical and Materials Engineering, University
of Nevada, Reno, Reno, Nevada 89557, United States
| | - Roger Rousseau
- Basic
& Applied Molecular Foundations, Physical and Computational Sciences
Directorate, Pacific Northwest National
Laboratory, Richland, Washington 99352, United States
| | - Vassiliki-Alexandra Glezakou
- Basic
& Applied Molecular Foundations, Physical and Computational Sciences
Directorate, Pacific Northwest National
Laboratory, Richland, Washington 99352, United States
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7
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Watkins LC, DeGrado WF, Voth GA. Multiscale Simulation of an Influenza A M2 Channel Mutant Reveals Key Features of Its Markedly Different Proton Transport Behavior. J Am Chem Soc 2022; 144:769-776. [PMID: 34985907 PMCID: PMC8834648 DOI: 10.1021/jacs.1c09281] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/21/2023]
Abstract
The influenza A M2 channel, a prototype for viroporins, is an acid-activated viroporin that conducts protons across the viral membrane, a critical step in the viral life cycle. Four central His37 residues control channel activation by binding subsequent protons from the viral exterior, which opens the Trp41 gate and allows proton flux to the interior. Asp44 is essential for maintaining the Trp41 gate in a closed state at high pH, resulting in asymmetric conduction. The prevalent D44N mutant disrupts this gate and opens the C-terminal end of the channel, resulting in increased conduction and a loss of this asymmetric conduction. Here, we use extensive Multiscale Reactive Molecular Dynamics (MS-RMD) and quantum mechanics/molecular mechanics (QM/MM) molecular dynamics simulations with an explicit, reactive excess proton to calculate the free energy of proton transport in this M2 mutant and to study the dynamic molecular-level behavior of D44N M2. We find that this mutation significantly lowers the barrier of His37 deprotonation in the activated state and shifts the barrier for entry to the Val27 tetrad. These free energy changes are reflected in structural shifts. Additionally, we show that the increased hydration around the His37 tetrad diminishes the effect of the His37 charge on the channel's water structure, facilitating proton transport and enabling activation from the viral interior. Altogether, this work provides key insight into the fundamental characteristics of PT in WT M2 and how the D44N mutation alters this PT mechanism, and it expands understanding of the role of emergent mutations in viroporins.
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Affiliation(s)
- Laura C. Watkins
- Department of Chemistry, Chicago Center for Theoretical Chemistry, Institute for Biophysical Dynamics and James Franck Institute, The University of Chicago, Chicago, Illinois 60637, United States
| | - William F. DeGrado
- Department of Pharmaceutical Chemistry, University of California, San Francisco, San Francisco, California, 94158, United States
| | - Gregory A. Voth
- Department of Chemistry, Chicago Center for Theoretical Chemistry, Institute for Biophysical Dynamics and James Franck Institute, The University of Chicago, Chicago, Illinois 60637, United States,Corresponding Author
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8
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Li C, Voth GA. Accurate and Transferable Reactive Molecular Dynamics Models from Constrained Density Functional Theory. J Phys Chem B 2021; 125:10471-10480. [PMID: 34520198 PMCID: PMC8480781 DOI: 10.1021/acs.jpcb.1c05992] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
![]()
Chemical reactions
constitute the central feature of many liquid,
material, and biomolecular processes. Conventional molecular dynamics
(MD) is inadequate for simulating chemical reactions given the fixed
bonding topology of most force fields, while modeling chemical reactions
using ab initio molecular dynamics is limited to
shorter time and length scales given its high computational cost.
As such, the multiscale reactive molecular dynamics method provides
one promising alternative for simulating complex chemical systems
at atomistic detail on a reactive potential energy surface. However,
the parametrization of such models is a key barrier to their applicability
and success. In this work, we present reactive MD models derived from
constrained density functional theory that are both accurate and transferable.
We illustrate the features of these models for proton dissociation
reactions of amino acids in both aqueous and protein environments.
Specifically, we present models for ionizable glutamate and lysine
that predict accurate absolute pKa values
in water as well as their significantly shifted pKa in staphylococcal nuclease (SNase) without any modification
of the models. As one outcome of the new methodology, the simulations
show that the deprotonation of ionizable residues in SNase can be
closely coupled with side chain rotations, which is a concept likely
generalizable to many other proteins. Furthermore, the present approach
is not limited to only pKa prediction
but can enable the fully atomistic simulation of many other reactive
systems along with a determination of the key aspects of the reaction
mechanisms.
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Affiliation(s)
- Chenghan Li
- Department of Chemistry, Chicago Center for Theoretical Chemistry, James Franck Institute, and Institute for Biophysical Dynamics, University of Chicago, Chicago, Illinois 60637, United States
| | - Gregory A Voth
- Department of Chemistry, Chicago Center for Theoretical Chemistry, James Franck Institute, and Institute for Biophysical Dynamics, University of Chicago, Chicago, Illinois 60637, United States
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9
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Li C, Voth GA. Using Constrained Density Functional Theory to Track Proton Transfers and to Sample Their Associated Free Energy Surface. J Chem Theory Comput 2021; 17:5759-5765. [PMID: 34468142 PMCID: PMC8444337 DOI: 10.1021/acs.jctc.1c00609] [Citation(s) in RCA: 6] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/20/2021] [Indexed: 11/30/2022]
Abstract
Ab initio molecular dynamics (AIMD) and quantum mechanics/molecular mechanics (QM/MM) methods are powerful tools for studying proton solvation, transfer, and transport processes in various environments. However, due to the high computational cost of such methods, achieving sufficient sampling of rare events involving excess proton motion-especially when Grotthuss proton shuttling is involved-usually requires enhanced free energy sampling methods to obtain informative results. Moreover, an appropriate collective variable (CV) that describes the effective position of the net positive charge defect associated with an excess proton is essential both for tracking the trajectory of the defect and for the free energy sampling of the processes associated with the resulting proton transfer and transport. In this work, such a CV is derived from first principles using constrained density functional theory (CDFT). This CV is applicable to a broad array of proton transport and transfer processes as studied via AIMD and QM/MM simulations.
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Affiliation(s)
- Chenghan Li
- Department of Chemistry,
Chicago Center for Theoretical Chemistry, James Franck Institute,
and Institute for Biophysical Dynamics, University of Chicago, Chicago, Illinois 60637, United States
| | - Gregory A. Voth
- Department of Chemistry,
Chicago Center for Theoretical Chemistry, James Franck Institute,
and Institute for Biophysical Dynamics, University of Chicago, Chicago, Illinois 60637, United States
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10
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Watkins LC, DeGrado WF, Voth GA. Influenza A M2 Inhibitor Binding Understood through Mechanisms of Excess Proton Stabilization and Channel Dynamics. J Am Chem Soc 2020; 142:17425-17433. [PMID: 32933245 PMCID: PMC7564090 DOI: 10.1021/jacs.0c06419] [Citation(s) in RCA: 16] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022]
Abstract
![]()
Prevalent resistance to inhibitors
that target the influenza A
M2 proton channel has necessitated a continued drug design effort,
supported by a sustained study of the mechanism of channel function
and inhibition. Recent high-resolution X-ray crystal structures present
the first opportunity to see how the adamantyl amine class of inhibitors
bind to M2 and disrupt and interact with the channel’s water
network, providing insight into the critical properties that enable
their effective inhibition in wild-type M2. In this work, we examine
the hypothesis that these drugs act primarily as mechanism-based inhibitors
by comparing hydrated excess proton stabilization during proton transport
in M2 with the interactions revealed in the crystal structures, using
the Multiscale Reactive Molecular Dynamics (MS-RMD) methodology. MS-RMD,
unlike classical molecular dynamics, models the hydrated proton (hydronium-like
cation) as a dynamic excess charge defect and allows bonds to break
and form, capturing the intricate interactions between the hydrated
excess proton, protein atoms, and water. Through this, we show that
the ammonium group of the inhibitors is effectively positioned to
take advantage of the channel’s natural ability to stabilize
an excess protonic charge and act as a hydronium mimic. Additionally,
we show that the channel is especially stable in the drug binding
region, highlighting the importance of this property for binding the
adamantane group. Finally, we characterize an additional hinge point
near Val27, which dynamically responds to charge and inhibitor binding.
Altogether, this work further illuminates a dynamic understanding
of the mechanism of drug inhibition in M2, grounded in the fundamental
properties that enable the channel to transport and stabilize excess
protons, with critical implications for future drug design efforts.
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Affiliation(s)
- Laura C Watkins
- Department of Chemistry, Chicago Center for Theoretical Chemistry, Institute for Biophysical Dynamics and James Franck Institute, The University of Chicago, Chicago, Illinois 60637, United States
| | - William F DeGrado
- Department of Pharmaceutical Chemistry, University of California, San Francisco, San Francisco, California 94158, United States
| | - Gregory A Voth
- Department of Chemistry, Chicago Center for Theoretical Chemistry, Institute for Biophysical Dynamics and James Franck Institute, The University of Chicago, Chicago, Illinois 60637, United States
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11
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Li C, Yue Z, Espinoza-Fonseca LM, Voth GA. Multiscale Simulation Reveals Passive Proton Transport Through SERCA on the Microsecond Timescale. Biophys J 2020; 119:1033-1040. [PMID: 32814059 DOI: 10.1016/j.bpj.2020.07.027] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/17/2020] [Revised: 07/20/2020] [Accepted: 07/24/2020] [Indexed: 12/11/2022] Open
Abstract
The sarcoplasmic reticulum Ca2+-ATPase (SERCA) transports two Ca2+ ions from the cytoplasm to the reticulum lumen at the expense of ATP hydrolysis. In addition to transporting Ca2+, SERCA facilitates bidirectional proton transport across the sarcoplasmic reticulum to maintain the charge balance of the transport sites and to balance the charge deficit generated by the exchange of Ca2+. Previous studies have shown the existence of a transient water-filled pore in SERCA that connects the Ca2+ binding sites with the lumen, but the capacity of this pathway to sustain passive proton transport has remained unknown. In this study, we used the multiscale reactive molecular dynamics method and free energy sampling to quantify the free energy profile and timescale of the proton transport across this pathway while also explicitly accounting for the dynamically coupled hydration changes of the pore. We find that proton transport from the central binding site to the lumen has a microsecond timescale, revealing a novel passive cytoplasm-to-lumen proton flow beside the well-known inverse proton countertransport occurring in active Ca2+ transport. We propose that this proton transport mechanism is operational and serves as a functional conduit for passive proton transport across the sarcoplasmic reticulum.
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Affiliation(s)
- Chenghan Li
- Department of Chemistry, Chicago Center for Theoretical Chemistry, James Franck Institute, and Institute for Biophysical Dynamics, The University of Chicago, Chicago, Illinois
| | - Zhi Yue
- Department of Chemistry, Chicago Center for Theoretical Chemistry, James Franck Institute, and Institute for Biophysical Dynamics, The University of Chicago, Chicago, Illinois
| | - L Michel Espinoza-Fonseca
- Center for Arrhythmia Research, Department of Internal Medicine, Division of Cardiovascular Medicine, University of Michigan, Ann Arbor, Michigan
| | - Gregory A Voth
- Department of Chemistry, Chicago Center for Theoretical Chemistry, James Franck Institute, and Institute for Biophysical Dynamics, The University of Chicago, Chicago, Illinois.
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12
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Li C, Swanson JMJ. Understanding and Tracking the Excess Proton in Ab Initio Simulations; Insights from IR Spectra. J Phys Chem B 2020; 124:5696-5708. [PMID: 32515957 PMCID: PMC7448536 DOI: 10.1021/acs.jpcb.0c03615] [Citation(s) in RCA: 13] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
Proton transport in aqueous media is ubiquitously important in chemical and biological processes. Although ab initio molecular dynamics (AIMD) simulations have made great progress in characterizing proton transport, there has been a long-standing challenge in defining and tracking the excess proton, or more properly, the center of excess charge (CEC) created when a hydrogen nucleus distorts the electron distributions of water molecules in a delocalized and highly dynamic nature. Yet, defining (and biasing) such a CEC is essential when combining AIMD with enhanced sampling methods to calculate the relevant macroscopic properties via free-energy landscapes, which is the standard practice for most processes of interest. Several CEC formulas have been proposed and used, but none have yet been systematically tested or rigorously derived. In this paper, we show that the CEC can be used as a computational tool to disentangle IR features of the solvated excess proton from its surrounding solvent, and in turn, how correlating the features in the excess charge spectrum with the behavior of CEC in simulations enables a systematic evaluation of various CEC definitions. We present a new definition of CEC and show how it overcomes the limitations of those currently available both from a spectroscopic point of view and from a practical perspective of performance in enhanced sampling simulations.
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Affiliation(s)
- Chenghan Li
- Department of Chemistry, Chicago Center for Theoretical Chemistry, James Franck Institute, and Institute for Biophysical Dynamics, The University of Chicago, Chicago, Illinois 60637, United States
| | - Jessica M. J. Swanson
- Department of Chemistry, Biological Chemistry Program, and Center for Cell and Genome Science, The University of Utah, Salt Lake City, Utah 84112, United States
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13
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Wang R, Carnevale V, Klein ML, Borguet E. First-Principles Calculation of Water p Ka Using the Newly Developed SCAN Functional. J Phys Chem Lett 2020; 11:54-59. [PMID: 31834803 DOI: 10.1021/acs.jpclett.9b02913] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/10/2023]
Abstract
Acid/base chemistry is an intriguing topic that still constitutes a challenge for computational chemistry. While estimating the acid dissociation constant (or pKa) could shed light on many chemistry processes, especially in the fields of biochemistry and geochemistry, evaluating the relative stability between protonated and nonprotonated species is often very difficult. Indeed, a prerequisite for calculating the pKa of any molecule is an accurate description of the energetics of water dissociation. Here, we applied constrained molecular dynamics simulations, a noncanonical sampling technique, to investigate the water deprotonation process by selecting the OH distance as the reaction coordinate. The calculation is based on density functional theory and the newly developed SCAN functional, which has shown excellent performance in describing water structure. This first benchmark of SCAN on a chemical reaction shows that this functional accurately models the energetics of proton transfer reactions in an aqueous environment. After taking Coulomb long-range corrections and nuclear quantum effects into account, the estimated water pKa is only 1.0 pKa unit different from the target experimental value. Our results show that the combination of SCAN and constrained MD successfully reproduces the chemistry of water and constitutes a good framework for calculating the free energy of chemical reactions of interest.
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Affiliation(s)
- Ruiyu Wang
- Department of Chemistry , Temple University , Philadelphia , Pennsylvania 19122 , United States
- Center for Complex Materials from First-Principles (CCM) , Temple University , 1925 North 12th Street , Philadelphia , Pennsylvania 19122 , United States
| | - Vincenzo Carnevale
- Institute for Computational Molecular Science , Temple University , Philadelphia , Pennsylvania 19122 , United States
- Department of Biology , Temple University , Philadelphia , Pennsylvania 19122 , United States
| | - Michael L Klein
- Department of Chemistry , Temple University , Philadelphia , Pennsylvania 19122 , United States
- Center for Complex Materials from First-Principles (CCM) , Temple University , 1925 North 12th Street , Philadelphia , Pennsylvania 19122 , United States
- Institute for Computational Molecular Science , Temple University , Philadelphia , Pennsylvania 19122 , United States
| | - Eric Borguet
- Department of Chemistry , Temple University , Philadelphia , Pennsylvania 19122 , United States
- Center for Complex Materials from First-Principles (CCM) , Temple University , 1925 North 12th Street , Philadelphia , Pennsylvania 19122 , United States
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14
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Yue Z, Li C, Voth GA, Swanson JMJ. Dynamic Protonation Dramatically Affects the Membrane Permeability of Drug-like Molecules. J Am Chem Soc 2019; 141:13421-13433. [PMID: 31382734 DOI: 10.1021/jacs.9b04387] [Citation(s) in RCA: 44] [Impact Index Per Article: 8.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
Abstract
Permeability (Pm) across biological membranes is of fundamental importance and a key factor in drug absorption, distribution, and development. Although the majority of drugs will be charged at some point during oral delivery, our understanding of membrane permeation by charged species is limited. The canonical model assumes that only neutral molecules partition into and passively permeate across membranes, but there is mounting evidence that these processes are also facile for certain charged species. However, it is unknown whether such ionizable permeants dynamically neutralize at the membrane surface or permeate in their charged form. To probe protonation-coupled permeation in atomic detail, we herein apply continuous constant-pH molecular dynamics along with free energy sampling to study the permeation of a weak base propranolol (PPL), and evaluate the impact of including dynamic protonation on Pm. The simulations reveal that PPL dynamically neutralizes at the lipid-tail interface, which dramatically influences the permeation free energy landscape and explains why the conventional model overestimates the assigned intrinsic permeability. We demonstrate how fixed-charge-state simulations can account for this effect, and propose a revised model that better describes pH-coupled partitioning and permeation. Our results demonstrate how dynamic changes in protonation state may play a critical role in the permeation of ionizable molecules, including pharmaceuticals and drug-like molecules, thus requiring a revision of the standard picture.
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Affiliation(s)
- Zhi Yue
- Department of Chemistry, James Frank Institute, and Institute for Biophysical Dynamics , The University of Chicago , Chicago , Illinois 60637 , United States
| | - Chenghan Li
- Department of Chemistry, James Frank Institute, and Institute for Biophysical Dynamics , The University of Chicago , Chicago , Illinois 60637 , United States
| | - Gregory A Voth
- Department of Chemistry, James Frank Institute, and Institute for Biophysical Dynamics , The University of Chicago , Chicago , Illinois 60637 , United States
| | - Jessica M J Swanson
- Department of Chemistry, James Frank Institute, and Institute for Biophysical Dynamics , The University of Chicago , Chicago , Illinois 60637 , United States
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15
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Watkins LC, Liang R, Swanson JMJ, DeGrado WF, Voth GA. Proton-Induced Conformational and Hydration Dynamics in the Influenza A M2 Channel. J Am Chem Soc 2019; 141:11667-11676. [PMID: 31264413 DOI: 10.1021/jacs.9b05136] [Citation(s) in RCA: 21] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022]
Abstract
The influenza A M2 protein is an acid-activated proton channel responsible for acidification of the inside of the virus, a critical step in the viral life cycle. This channel has four central histidine residues that form an acid-activated gate, binding protons from the outside until an activated state allows proton transport to the inside. While previous work has focused on proton transport through the channel, the structural and dynamic changes that accompany proton flux and enable activation have yet to be resolved. In this study, extensive Multiscale Reactive Molecular Dynamics simulations with explicit Grotthuss-shuttling hydrated excess protons are used to explore detailed molecular-level interactions that accompany proton transport in the +0, + 1, and +2 histidine charge states. The results demonstrate how the hydrated excess proton strongly influences both the protein and water hydrogen-bonding network throughout the channel, providing further insight into the channel's acid-activation mechanism and rectification behavior. We find that the excess proton dynamically, as a function of location, shifts the protein structure away from its equilibrium distributions uniquely for different pH conditions consistent with acid-activation. The proton distribution in the xy-plane is also shown to be asymmetric about the channel's main axis, which has potentially important implications for the mechanism of proton conduction and future drug design efforts.
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Affiliation(s)
- Laura C Watkins
- Department of Chemistry, Institute for Biophysical Dynamics and James Franck Institute , The University of Chicago , Chicago , Illinois 60637 , United States
| | - Ruibin Liang
- Department of Chemistry, Institute for Biophysical Dynamics and James Franck Institute , The University of Chicago , Chicago , Illinois 60637 , United States
| | - Jessica M J Swanson
- Department of Chemistry, Institute for Biophysical Dynamics and James Franck Institute , The University of Chicago , Chicago , Illinois 60637 , United States
| | - William F DeGrado
- Department of Pharmaceutical Chemistry , University of California , San Francisco , California 94158 , United States
| | - Gregory A Voth
- Department of Chemistry, Institute for Biophysical Dynamics and James Franck Institute , The University of Chicago , Chicago , Illinois 60637 , United States
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16
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Wang Z, Swanson JMJ, Voth GA. Modulating the Chemical Transport Properties of a Transmembrane Antiporter via Alternative Anion Flux. J Am Chem Soc 2018; 140:16535-16543. [PMID: 30421606 PMCID: PMC6379079 DOI: 10.1021/jacs.8b07614] [Citation(s) in RCA: 21] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/16/2023]
Abstract
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ClC-ec1 is a prototype of the ClC
antiporters, proteins that stoichiometrically
exchange Cl– and H+ ions in opposite
directions across a membrane. It has been shown that other polyatomic
anions, such as NO3– and SCN–, can also be transported by ClC-ec1, but with partially or completely
uncoupled proton flux. Herein, with the help of multiscale computer
simulations in which the Grotthuss mechanism of proton transport (PT)
is treated explicitly, we demonstrate how the chemical nature of these
anions alters the coupling mechanism and qualitatively explain the
shifts in the ion stoichiometry. Multidimensional free energy profiles
for PT and the coupled changes in hydration are presented for NO3– and SCN–. The calculated
proton conductances agree with experiment, showing reduced or abolished
proton flux. Surprisingly, the proton affinity of the anion is less
influential on the PT, while its size and interactions with the protein
significantly alter hydration and shift its influence on PT from facilitating
to inhibiting. We find that the hydration of the cavity below the
anion is relatively fast, but connecting the water network past the
steric hindrance of these polyatomic anions is quite slow. Hence,
the most relevant coordinate to the PT free energy barrier is the
water connectivity along the PT pathway, but importantly only in the
presence of the excess proton, and this coordinate is significantly
affected by the nature of the bound anion. This work again demonstrates
how PT is intrinsically coupled with protein cavity hydration changes
as well as influenced by the protein environment. It additionally
suggests ways in which ion exchange can be modulated and exchange
stoichiometries altered.
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Affiliation(s)
- Zhi Wang
- Department of Chemistry, James Franck Institute, and Institute for Biophysical Dynamics , The University of Chicago , Chicago , Illinois 60637 , United States
| | - Jessica M J Swanson
- Department of Chemistry, James Franck Institute, and Institute for Biophysical Dynamics , The University of Chicago , Chicago , Illinois 60637 , United States
| | - Gregory A Voth
- Department of Chemistry, James Franck Institute, and Institute for Biophysical Dynamics , The University of Chicago , Chicago , Illinois 60637 , United States
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17
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Nelson JG, Peng Y, Silverstein DW, Swanson JMJ. Correction to Multiscale Reactive Molecular Dynamics for Absolute p Ka Predictions and Amino Acid Deprotonation. J Chem Theory Comput 2018; 14:1169. [PMID: 29392951 PMCID: PMC8154317 DOI: 10.1021/acs.jctc.8b00044] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
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18
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Yang X, Rees RJ, Conway W, Puxty G, Yang Q, Winkler DA. Computational Modeling and Simulation of CO2 Capture by Aqueous Amines. Chem Rev 2017; 117:9524-9593. [PMID: 28517929 DOI: 10.1021/acs.chemrev.6b00662] [Citation(s) in RCA: 68] [Impact Index Per Article: 9.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022]
Affiliation(s)
- Xin Yang
- CSIRO Manufacturing, Bayview Avenue, Clayton 3169, Australia
- College
of Chemistry, Key Lab of Green Chemistry and Technology in Ministry
of Education, Sichuan University, Chengdu 610064, People’s Republic of China
| | - Robert J. Rees
- Data61
- CSIRO, Door 34 Goods
Shed, Village Street, Docklands VIC 3008, Australia
| | | | | | - Qi Yang
- CSIRO Manufacturing, Bayview Avenue, Clayton 3169, Australia
| | - David A. Winkler
- CSIRO Manufacturing, Bayview Avenue, Clayton 3169, Australia
- Monash Institute of Pharmaceutical Sciences, 392 Royal Parade, Parkville 3052, Australia
- Latrobe Institute for Molecular Science, Bundoora 3046, Australia
- School
of
Chemical and Physical Science, Flinders University, Bedford Park 5042, Australia
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19
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van Keulen SC, Gianti E, Carnevale V, Klein ML, Rothlisberger U, Delemotte L. Does Proton Conduction in the Voltage-Gated H + Channel hHv1 Involve Grotthuss-Like Hopping via Acidic Residues? J Phys Chem B 2017; 121:3340-3351. [PMID: 27801578 PMCID: PMC6310143 DOI: 10.1021/acs.jpcb.6b08339] [Citation(s) in RCA: 27] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Hv1s are ubiquitous highly selective voltage-gated proton channels involved in male fertility, immunology, and the invasiveness of certain forms of breast cancer. The mechanism of proton extrusion in Hv1 is not yet understood, while it constitutes the first step toward the design of high-affinity drugs aimed at this important pharmacological target. In this contribution, we explore the details of the mechanism via an integrative approach, using classical and QM/MM molecular dynamics simulations of a monomeric hHv1 model. We propose that protons localize in three binding sites along the channel lumen, formed by three pairs of conserved negatively charged residues lining the pore: D174/E153, D112/D185, and E119/D123. Local rearrangements, involving notably a dihedral transition of F150, a conserved phenylalanine lining the permeation pathway, appear to allow protons to hop from one acidic residue to the next through a bridging water molecule. These results constitute a first attempt at rationalizing hHv1 selectivity for H+ and the role played by D112 in this process. They pave the way for further quantitative characterization of H+ transport in hHv1.
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Affiliation(s)
- Siri C. van Keulen
- Laboratory of Computational Chemistry and Biochemistry, Institute of Chemical Sciences and Engineering, École Polytechnique Fédérale de Lausanne (EPFL), CH-1015 Lausanne, Switzerland
| | - Eleonora Gianti
- Institute for Computational Molecular Science, Department of Chemistry, Temple University, Philadelphia, PA 19122
| | - Vincenzo Carnevale
- Institute for Computational Molecular Science, Department of Chemistry, Temple University, Philadelphia, PA 19122
| | - Michael L. Klein
- Institute for Computational Molecular Science, Department of Chemistry, Temple University, Philadelphia, PA 19122
| | - Ursula Rothlisberger
- Laboratory of Computational Chemistry and Biochemistry, Institute of Chemical Sciences and Engineering, École Polytechnique Fédérale de Lausanne (EPFL), CH-1015 Lausanne, Switzerland
| | - Lucie Delemotte
- Laboratory of Computational Chemistry and Biochemistry, Institute of Chemical Sciences and Engineering, École Polytechnique Fédérale de Lausanne (EPFL), CH-1015 Lausanne, Switzerland
- Present address: Science for Life Laboratory, Department of Theoretical Physics, KTH, Box 1031, SE-171 21 Solna, Stockholm, Sweden
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20
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Sun R, Sode O, Dama JF, Voth GA. Simulating Protein Mediated Hydrolysis of ATP and Other Nucleoside Triphosphates by Combining QM/MM Molecular Dynamics with Advances in Metadynamics. J Chem Theory Comput 2017; 13:2332-2341. [PMID: 28345907 PMCID: PMC5425946 DOI: 10.1021/acs.jctc.7b00077] [Citation(s) in RCA: 28] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Abstract
The protein mediated hydrolysis of nucleoside triphosphates such as ATP or GTP is one of the most important and challenging biochemical reactions in nature. The chemical environment (water structure, catalytic metal, and amino acid residues) adjacent to the hydrolysis site contains hundreds of atoms, usually greatly limiting the amount of the free energy sampling that one can achieve from computationally demanding electronic structure calculations such as QM/MM simulations. Therefore, the combination of QM/MM molecular dynamics with the recently developed transition-tempered metadynamics (TTMetaD), an enhanced sampling method that can provide a high-quality free energy estimate at an early stage in a simulation, is an ideal approach to address the biomolecular nucleoside triphosphate hydrolysis problem. In this work the ATP hydrolysis process in monomeric and filamentous actin is studied as an example application of the combined methodology. The performance of TTMetaD in these demanding QM/MM simulations is compared with that of the more conventional well-tempered metadynamics (WTMetaD). Our results show that TTMetaD exhibits much better exploration of the hydrolysis reaction free energy surface in two key collective variables (CVs) during the early stages of the QM/MM simulation than does WTMetaD. The TTMetaD simulations also reveal that a key third degree of freedom, the O-H bond-breaking and proton transfer from the lytic water, must be biased for TTMetaD to converge fully. To perturb the NTP hydrolysis dynamics to the least extent and to properly focus the MetaD free energy sampling, we also adopt here the recently developed metabasin metadynamics (MBMetaD) to construct a self-limiting bias potential that only applies to the lytic water after its nucleophilic attack of the phosphate of ATP. With these new, state-of-the-art enhanced sampling metadynamics techniques, we present an effective and accurate computational strategy for combining QM/MM molecular dynamics simulation with free energy sampling methodology, including a means to analyze the convergence of the calculations through robust numerical criteria.
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Affiliation(s)
- Rui Sun
- Department of Chemistry, James Franck Institute, and Institute for Biophysical Dynamics, The University of Chicago , 5735 South Ellis Avenue, Chicago, Illinois 60637, United States
| | - Olaseni Sode
- Department of Chemistry, James Franck Institute, and Institute for Biophysical Dynamics, The University of Chicago , 5735 South Ellis Avenue, Chicago, Illinois 60637, United States
| | - James F Dama
- Department of Chemistry, James Franck Institute, and Institute for Biophysical Dynamics, The University of Chicago , 5735 South Ellis Avenue, Chicago, Illinois 60637, United States
| | - Gregory A Voth
- Department of Chemistry, James Franck Institute, and Institute for Biophysical Dynamics, The University of Chicago , 5735 South Ellis Avenue, Chicago, Illinois 60637, United States
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21
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Estimation of the racemization rate constants for α-amino acids using Density Functional Theory. COMPUT THEOR CHEM 2017. [DOI: 10.1016/j.comptc.2017.01.034] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
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22
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Multiscale Simulations Reveal Key Aspects of the Proton Transport Mechanism in the ClC-ec1 Antiporter. Biophys J 2016; 110:1334-45. [PMID: 27028643 DOI: 10.1016/j.bpj.2016.02.014] [Citation(s) in RCA: 44] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/06/2015] [Revised: 02/05/2016] [Accepted: 02/08/2016] [Indexed: 11/22/2022] Open
Abstract
Multiscale reactive molecular dynamics simulations are used to study proton transport through the central region of ClC-ec1, a widely studied ClC transporter that enables the stoichiometric exchange of 2 Cl(-) ions for 1 proton (H(+)). It has long been known that both Cl(-) and proton transport occur through partially congruent pathways, and that their exchange is strictly coupled. However, the nature of this coupling and the mechanism of antiporting remain topics of debate. Here multiscale simulations have been used to characterize proton transport between E203 (Glu(in)) and E148 (Glu(ex)), the internal and external intermediate proton binding sites, respectively. Free energy profiles are presented, explicitly accounting for the binding of Cl(-) along the central pathway, the dynamically coupled hydration changes of the central region, and conformational changes of Glu(in) and Glu(ex). We find that proton transport between Glu(in) and Glu(ex) is possible in both the presence and absence of Cl(-) in the central binding site, although it is facilitated by the anion presence. These results support the notion that the requisite coupling between Cl(-) and proton transport occurs elsewhere (e.g., during proton uptake or release). In addition, proton transport is explored in the E203K mutant, which maintains proton permeation despite the substitution of a basic residue for Glu(in). This collection of calculations provides for the first time, to our knowledge, a detailed picture of the proton transport mechanism in the central region of ClC-ec1 at a molecular level.
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23
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Liang R, Swanson JMJ, Madsen JJ, Hong M, DeGrado WF, Voth GA. Acid activation mechanism of the influenza A M2 proton channel. Proc Natl Acad Sci U S A 2016; 113:E6955-E6964. [PMID: 27791184 PMCID: PMC5111692 DOI: 10.1073/pnas.1615471113] [Citation(s) in RCA: 70] [Impact Index Per Article: 8.8] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022] Open
Abstract
The homotetrameric influenza A M2 channel (AM2) is an acid-activated proton channel responsible for the acidification of the influenza virus interior, an important step in the viral lifecycle. Four histidine residues (His37) in the center of the channel act as a pH sensor and proton selectivity filter. Despite intense study, the pH-dependent activation mechanism of the AM2 channel has to date not been completely understood at a molecular level. Herein we have used multiscale computer simulations to characterize (with explicit proton transport free energy profiles and their associated calculated conductances) the activation mechanism of AM2. All proton transfer steps involved in proton diffusion through the channel, including the protonation/deprotonation of His37, are explicitly considered using classical, quantum, and reactive molecular dynamics methods. The asymmetry of the proton transport free energy profile under high-pH conditions qualitatively explains the rectification behavior of AM2 (i.e., why the inward proton flux is allowed when the pH is low in viral exterior and high in viral interior, but outward proton flux is prohibited when the pH gradient is reversed). Also, in agreement with electrophysiological results, our simulations indicate that the C-terminal amphipathic helix does not significantly change the proton conduction mechanism in the AM2 transmembrane domain; the four transmembrane helices flanking the channel lumen alone seem to determine the proton conduction mechanism.
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Affiliation(s)
- Ruibin Liang
- Department of Chemistry, The University of Chicago, Chicago, IL 60637
- Institute for Biophysical Dynamics, The University of Chicago, Chicago, IL 60637
- James Franck Institute, The University of Chicago, Chicago, IL 60637
| | - Jessica M J Swanson
- Department of Chemistry, The University of Chicago, Chicago, IL 60637
- Institute for Biophysical Dynamics, The University of Chicago, Chicago, IL 60637
- James Franck Institute, The University of Chicago, Chicago, IL 60637
| | - Jesper J Madsen
- Department of Chemistry, The University of Chicago, Chicago, IL 60637
- Institute for Biophysical Dynamics, The University of Chicago, Chicago, IL 60637
- James Franck Institute, The University of Chicago, Chicago, IL 60637
| | - Mei Hong
- Department of Chemistry, Massachusetts Institute of Technology, Cambridge, MA 02139
| | - William F DeGrado
- Department of Pharmaceutical Chemistry, University of San Francisco, San Francisco, CA 94158
| | - Gregory A Voth
- Department of Chemistry, The University of Chicago, Chicago, IL 60637;
- Institute for Biophysical Dynamics, The University of Chicago, Chicago, IL 60637
- James Franck Institute, The University of Chicago, Chicago, IL 60637
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24
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Lee S, Mayes HB, Swanson JMJ, Voth GA. The Origin of Coupled Chloride and Proton Transport in a Cl -/H + Antiporter. J Am Chem Soc 2016; 138:14923-14930. [PMID: 27783900 PMCID: PMC5114699 DOI: 10.1021/jacs.6b06683] [Citation(s) in RCA: 31] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
![]()
The ClC family of transmembrane proteins
functions throughout nature
to control the transport of Cl– ions across biological
membranes. ClC-ec1 from Escherichia coli is an antiporter,
coupling the transport of Cl– and H+ ions
in opposite directions and driven by the concentration gradients of
the ions. Despite keen interest in this protein, the molecular mechanism
of the Cl–/H+ coupling has not been fully
elucidated. Here, we have used multiscale simulation to help identify
the essential mechanism of the Cl–/H+ coupling. We find that the highest barrier for proton transport
(PT) from the intra- to extracellular solution is attributable to
a chemical reaction, the deprotonation of glutamic acid 148 (E148).
This barrier is significantly reduced by the binding of Cl– in the “central” site (Cl–cen), which displaces E148 and thereby facilitates its deprotonation.
Conversely, in the absence of Cl–cen E148
favors the “down” conformation, which results in a much
higher cumulative rotation and deprotonation barrier that effectively
blocks PT to the extracellular solution. Thus, the rotation of E148
plays a critical role in defining the Cl–/H+ coupling. As a control, we have also simulated PT in the
ClC-ec1 E148A mutant to further understand the role of this residue.
Replacement with a non-protonatable residue greatly increases the
free energy barrier for PT from E203 to the extracellular solution,
explaining the experimental result that PT in E148A is blocked whether
or not Cl–cen is present. The results
presented here suggest both how a chemical reaction can control the
rate of PT and also how it can provide a mechanism for a coupling
of the two ion transport processes.
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Affiliation(s)
- Sangyun Lee
- Department of Chemistry, James Franck Institute, and Institute for Biophysical Dynamics, The University of Chicago , Chicago, Illinois 60637, United States
| | - Heather B Mayes
- Department of Chemistry, James Franck Institute, and Institute for Biophysical Dynamics, The University of Chicago , Chicago, Illinois 60637, United States
| | - Jessica M J Swanson
- Department of Chemistry, James Franck Institute, and Institute for Biophysical Dynamics, The University of Chicago , Chicago, Illinois 60637, United States
| | - Gregory A Voth
- Department of Chemistry, James Franck Institute, and Institute for Biophysical Dynamics, The University of Chicago , Chicago, Illinois 60637, United States
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25
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Linear Response Function of Bond-Order. Int J Mol Sci 2016; 17:ijms17111779. [PMID: 27792148 PMCID: PMC5133780 DOI: 10.3390/ijms17111779] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/31/2016] [Revised: 10/12/2016] [Accepted: 10/14/2016] [Indexed: 11/16/2022] Open
Abstract
We present the linear response function of bond-orders (LRF-BO) based on a real space integration scheme for molecular systems. As in the case of the LRF of density, the LRF-BO is defined as the response of the bond order of the molecule for the virtual perturbation. Our calculations show that the LRF-BO enables us not only to detect inductive and resonating effects of conjugating systems, but also to predict pKa values on substitution groups via linear relationships between the Hammett constants and the LRF-BO values for meta- and para-substituted benzoic acids. More importantly, the LRF-BO values for the O-H bonds strongly depend on the sites to which the virtual perturbation is applied, implying that the LRF-BO values include essential information about reaction mechanism of the acid-dissociation of substituted benzoic acids.
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26
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Multiscale simulations reveal key features of the proton-pumping mechanism in cytochrome c oxidase. Proc Natl Acad Sci U S A 2016; 113:7420-5. [PMID: 27339133 DOI: 10.1073/pnas.1601982113] [Citation(s) in RCA: 49] [Impact Index Per Article: 6.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Cytochrome c oxidase (CcO) reduces oxygen to water and uses the released free energy to pump protons across the membrane. We have used multiscale reactive molecular dynamics simulations to explicitly characterize (with free-energy profiles and calculated rates) the internal proton transport events that enable proton pumping during first steps of oxidation of the fully reduced enzyme. Our results show that proton transport from amino acid residue E286 to both the pump loading site (PLS) and to the binuclear center (BNC) are thermodynamically driven by electron transfer from heme a to the BNC, but that the former (i.e., pumping) is kinetically favored whereas the latter (i.e., transfer of the chemical proton) is rate-limiting. The calculated rates agree with experimental measurements. The backflow of the pumped proton from the PLS to E286 and from E286 to the inside of the membrane is prevented by large free-energy barriers for the backflow reactions. Proton transport from E286 to the PLS through the hydrophobic cavity and from D132 to E286 through the D-channel are found to be strongly coupled to dynamical hydration changes in the corresponding pathways and, importantly, vice versa.
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27
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Lee S, Liang R, Voth GA, Swanson JMJ. Computationally Efficient Multiscale Reactive Molecular Dynamics to Describe Amino Acid Deprotonation in Proteins. J Chem Theory Comput 2016; 12:879-91. [PMID: 26734942 PMCID: PMC4750100 DOI: 10.1021/acs.jctc.5b01109] [Citation(s) in RCA: 42] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/21/2015] [Indexed: 11/30/2022]
Abstract
An important challenge in the simulation of biomolecular systems is a quantitative description of the protonation and deprotonation process of amino acid residues. Despite the seeming simplicity of adding or removing a positively charged hydrogen nucleus, simulating the actual protonation/deprotonation process is inherently difficult. It requires both the explicit treatment of the excess proton, including its charge defect delocalization and Grotthuss shuttling through inhomogeneous moieties (water and amino residues), and extensive sampling of coupled condensed phase motions. In a recent paper (J. Chem. Theory Comput. 2014, 10, 2729-2737), a multiscale approach was developed to map high-level quantum mechanics/molecular mechanics (QM/MM) data into a multiscale reactive molecular dynamics (MS-RMD) model in order to describe amino acid deprotonation in bulk water. In this article, we extend the fitting approach (called FitRMD) to create MS-RMD models for ionizable amino acids within proteins. The resulting models are shown to faithfully reproduce the free energy profiles of the reference QM/MM Hamiltonian for PT inside an example protein, the ClC-ec1 H(+)/Cl(-) antiporter. Moreover, we show that the resulting MS-RMD models are computationally efficient enough to then characterize more complex 2-dimensional free energy surfaces due to slow degrees of freedom such as water hydration of internal protein cavities that can be inherently coupled to the excess proton charge translocation. The FitRMD method is thus shown to be an effective way to map ab initio level accuracy into a much more computationally efficient reactive MD method in order to explicitly simulate and quantitatively describe amino acid protonation/deprotonation in proteins.
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Affiliation(s)
| | | | - Gregory A. Voth
- Department of Chemistry,
Institute for Biophysical Dynamics, James Franck Institute, and Computation
Institute, University of Chicago, 5735 S. Ellis Avenue, Chicago, Illinois 60637, United States
| | - Jessica M. J. Swanson
- Department of Chemistry,
Institute for Biophysical Dynamics, James Franck Institute, and Computation
Institute, University of Chicago, 5735 S. Ellis Avenue, Chicago, Illinois 60637, United States
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28
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Tummanapelli AK, Vasudevan S. Ab Initio Molecular Dynamics Simulations of Amino Acids in Aqueous Solutions: Estimating pKa Values from Metadynamics Sampling. J Phys Chem B 2015; 119:12249-55. [PMID: 26331783 DOI: 10.1021/acs.jpcb.5b05211] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Changes in the protonation and deprotonation of amino acid residues in proteins play a key role in many biological processes and pathways. Here, we report calculations of the free-energy profile for the protonation-deprotonation reaction of the 20 canonical α amino acids in aqueous solutions using ab initio Car-Parrinello molecular dynamics simulations coupled with metadynamics sampling. We show here that the calculated change in free energy of the dissociation reaction provides estimates of the multiple pKa values of the amino acids that are in good agreement with experiment. We use the bond-length-dependent number of the protons coordinated to the hydroxyl oxygen of the carboxylic and the amine groups as the collective variables to explore the free-energy profiles of the Bronsted acid-base chemistry of amino acids in aqueous solutions. We ensure that the amino acid undergoing dissociation is solvated by at least three hydrations shells with all water molecules included in the simulations. The method works equally well for amino acids with neutral, acidic and basic side chains and provides estimates of the multiple pKa values with a mean relative error, with respect to experimental results, of 0.2 pKa units.
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Affiliation(s)
- Anil Kumar Tummanapelli
- Department of Inorganic and Physical Chemistry, Indian Institute of Science , Bangalore 560012, India
| | - Sukumaran Vasudevan
- Department of Inorganic and Physical Chemistry, Indian Institute of Science , Bangalore 560012, India
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29
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Tummanapelli AK, Vasudevan S. Estimating successive pKa values of polyprotic acids from ab initio molecular dynamics using metadynamics: the dissociation of phthalic acid and its isomers. Phys Chem Chem Phys 2015; 17:6383-8. [DOI: 10.1039/c4cp06000h] [Citation(s) in RCA: 33] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/04/2023]
Abstract
pKa values of polyprotic acids estimated from ab initio molecular dynamics computation of the change in free energy upon dissociation.
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Affiliation(s)
- Anil Kumar Tummanapelli
- Department of Inorganic and Physical Chemistry
- Indian Institute of Science
- Bangalore 560012
- India
| | - Sukumaran Vasudevan
- Department of Inorganic and Physical Chemistry
- Indian Institute of Science
- Bangalore 560012
- India
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30
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Méndez-Hurtado J, Menéndez MI, López R, Ruiz-López MF. Unraveling the intramolecular cyclization mechanism of oxidized tryptophan in aqueous solution as a function of pH. Org Biomol Chem 2015; 13:8695-702. [DOI: 10.1039/c5ob01193k] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
pH tunes the mechanism of the intramolecular cyclization of 3a-substituted tryptophan derivatives.
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Affiliation(s)
| | - M. Isabel Menéndez
- Departamento de Química Física y Analítica
- Universidad de Oviedo
- 33006 Oviedo
- Spain
| | - Ramón López
- Departamento de Química Física y Analítica
- Universidad de Oviedo
- 33006 Oviedo
- Spain
| | - Manuel F. Ruiz-López
- Theoretical Chemistry and Biochemistry Group
- SRSMC
- Nancy-University CNRS
- 54506 Vandoeuvre-lès-Nancy Cedex
- France
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31
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Sode O, Voth GA. Electron transfer activation of a second water channel for proton transport in [FeFe]-hydrogenase. J Chem Phys 2014; 141:22D527. [DOI: 10.1063/1.4902236] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022] Open
Affiliation(s)
- Olaseni Sode
- Department of Chemistry, James Franck Institute, Institute for Biophysical Dynamics, Computation Institute, The University of Chicago, Chicago, Illinois 60637, USA and Computing, Environment and Life Sciences, Argonne National Laboratory, Argonne, Illinois 60439, USA
| | - Gregory A. Voth
- Department of Chemistry, James Franck Institute, Institute for Biophysical Dynamics, Computation Institute, The University of Chicago, Chicago, Illinois 60637, USA and Computing, Environment and Life Sciences, Argonne National Laboratory, Argonne, Illinois 60439, USA
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32
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Tummanapelli AK, Vasudevan S. Dissociation Constants of Weak Acids from ab Initio Molecular Dynamics Using Metadynamics: Influence of the Inductive Effect and Hydrogen Bonding on pKa Values. J Phys Chem B 2014; 118:13651-7. [DOI: 10.1021/jp5088898] [Citation(s) in RCA: 41] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022]
Affiliation(s)
- Anil Kumar Tummanapelli
- Department of Inorganic and
Physical Chemistry, Indian Institute of Science, Bangalore 560012, India
| | - Sukumaran Vasudevan
- Department of Inorganic and
Physical Chemistry, Indian Institute of Science, Bangalore 560012, India
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