1
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Liu X, Brooks Iii CL. Enhanced Sampling of Buried Charges in Free Energy Calculations Using Replica Exchange with Charge Tempering. J Chem Theory Comput 2024; 20:1051-1061. [PMID: 38232295 PMCID: PMC11275198 DOI: 10.1021/acs.jctc.3c00993] [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] [Indexed: 01/19/2024]
Abstract
Buried ionizable groups in proteins often play important structural and functional roles. However, it is generally challenging to study the detailed molecular mechanisms solely based on experimental measurements. Free energy calculations using atomistic simulations, on the other hand, complement experimental studies and can provide high temporal and spatial resolution information that can lead to mechanistic insights. Nevertheless, it is also well recognized that sufficient sampling of such atomistic simulations can be challenging, considering that structural changes related to the buried charges may be very slow. In the present study, we describe a simple but effective enhanced sampling technique called replica exchange with charge tempering (REChgT) with a novel free energy method, multisite λ dynamics (MSλD), to study two systems containing buried charges, pKa prediction of a small molecule, orotate, in complex with the dihydroorotate dehydrogenase, and relative stability of a Glu-Lys pair buried in the hydrophobic core of two variants of Staphylococcal nuclease. Compared to the original MSλD simulations, the usage of REChgT dramatically increases sampling in both conformational and alchemical spaces, which directly translates into a significant reduction of wall time to converge the free energy calculations. This study highlights the importance of sufficient sampling toward developing improved free energy methods.
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Affiliation(s)
- Xiaorong Liu
- Department of Chemistry, University of Michigan, Ann Arbor, Michigan 48109, United States
| | - Charles L Brooks Iii
- Department of Chemistry, University of Michigan, Ann Arbor, Michigan 48109, United States
- Biophysics Program, University of Michigan, Ann Arbor, Michigan 48109, United States
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2
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Li T, Yu L, Sun J, Liu J, He X. Ionization of D571 Is Coupled with SARS-CoV-2 Spike Up/Down Equilibrium Revealing the pH-Dependent Allosteric Mechanism of Receptor-Binding Domains. J Phys Chem B 2022; 126:4828-4839. [PMID: 35736566 PMCID: PMC9236204 DOI: 10.1021/acs.jpcb.2c02365] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/07/2022] [Revised: 06/05/2022] [Indexed: 11/30/2022]
Abstract
As a type I viral fusion protein, SARS-CoV-2 spike undergoes a pH-dependent switch to mediate the endosomal positioning of the receptor-binding domain to facilitate viral entry into cells and immune evasion. Gaps in our knowledge concerning the conformational transitions and key intramolecular motivations have hampered the development of effective therapeutics against the virus. To clarify the pH-sensitive elements on spike-gating the receptor-binding domain (RBD) opening and understand the details of the RBD opening transition, we performed microsecond-time scale constant pH molecular dynamics simulations in this study. We identified the deeply buried D571 with a clear pKa shift, suggesting a potential pH sensor, and showed the coupling of ionization of D571 with spike RBD-up/down equilibrium. We also computed the free-energy landscape for RBD opening and identified the crucial interactions that influence RBD dynamics. The atomic-level characterization of the pH-dependent spike activation mechanism provided herein offers new insights for a better understanding of the fundamental mechanisms of SARS-CoV-2 viral entry and infection and hence supports the discovery of novel therapeutics for COVID-19.
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Affiliation(s)
- Tong Li
- School of Traditional Chinese Pharmacy,
China Pharmaceutical University, Nanjing 210009,
China
| | - Lan Yu
- School of Science, China Pharmaceutical
University, Nanjing 210009, China
| | - Jingfang Sun
- School of Basic Medicine and Clinical Pharmacy,
China Pharmaceutical University, Nanjing 210009,
China
| | - Jinfeng Liu
- School of Basic Medicine and Clinical Pharmacy,
China Pharmaceutical University, Nanjing 210009,
China
| | - Xiao He
- Shanghai Engineering Research Center of Molecular
Therapeutics and New Drug Development, Shanghai Frontiers Science Center of Molecule
Intelligent Syntheses, School of Chemistry and Molecular Engineering, East
China Normal University, Shanghai 200062, China
- New York University-East China Normal University
Center for Computational Chemistry, New York University
Shanghai, Shanghai 200062, China
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3
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Zhang B, Peng Y, Wang Y, Wang X. Exploring the trimerization process of a transmembrane helix with an ionizable residue by molecular dynamics simulations: a case study of transmembrane domain 5 of LMP-1. Phys Chem Chem Phys 2022; 24:7084-7092. [PMID: 35262149 DOI: 10.1039/d2cp00102k] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
The oligomerization of membrane proteins is an important biological process that plays a critical role in the initialization of membrane protein receptor signaling. Unveiling how transmembrane segments oligomerize is critical for understanding the mechanism of membrane receptor signaling activation. Owing to the complicated membrane environment and the extraordinary dynamic properties of the ionizable residues in the transmembrane segment, it is extremely challenging to thoroughly understand the oligomerization process of the transmembrane domain. In this study, transmembrane domain 5 (TMD5) of latent membrane protein-1 from Epstein-Barr virus was used as a prototype model to investigate the trimerization process of the transmembrane segment with ionizable residues. The trimerization process of TMD5 was rebuilt and investigated via conventional molecular dynamics simulations and constant-pH molecular dynamics simulations. When TMD5s approached each other, the tilting angles of the TMD5 monomer decreased. TMD5s formed stable trimers until two interacting sites (D150s and Q139s) along each transmembrane helix were created to lock the TMD5s. The pKa values of D150 shifted toward neutral states in the membrane environment. When TMD5s were monomers, the pKa shift of D150 was mainly influenced by its microenvironment in the lipid bilayer. When TMD5s were moving close to each other, protein-protein interactions became the main contributing factor for the pKa shift of D150s. Overall, this work elucidates the behavior of the TMD5 helix and the pKa shift of ionizable residue D150 in the process of TMD5 oligomerization. This study may provide insight into the development of agents for targeting the oligomerization of membrane proteins.
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Affiliation(s)
- Bo Zhang
- Laboratory of Chemical Biology, Changchun Institute of Applied Chemistry, Chinese Academy of Sciences, Changchun, Jilin, 130022, China. .,Department of Applied Chemistry and Engineering, University of Science and Technology of China, Hefei, Anhui, 230026, China
| | - Yinghua Peng
- State Key Laboratory for Molecular Biology of Special Economic Animal, Institute of Special Animal and Plant Sciences, Chinese Academy of Agricultural Sciences, Changchun, Jilin, 130112, China
| | - Yibo Wang
- Laboratory of Chemical Biology, Changchun Institute of Applied Chemistry, Chinese Academy of Sciences, Changchun, Jilin, 130022, China.
| | - Xiaohui Wang
- Laboratory of Chemical Biology, Changchun Institute of Applied Chemistry, Chinese Academy of Sciences, Changchun, Jilin, 130022, China. .,Department of Applied Chemistry and Engineering, University of Science and Technology of China, Hefei, Anhui, 230026, China.,Beijing National Laboratory for Molecular Sciences, Beijing, 100190, China
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4
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Frazee N, Mertz B. Intramolecular interactions play key role in stabilization of pHLIP at acidic conditions. J Comput Chem 2021; 42:1809-1816. [PMID: 34245047 DOI: 10.1002/jcc.26719] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/23/2020] [Revised: 04/30/2021] [Accepted: 06/21/2021] [Indexed: 12/12/2022]
Abstract
The pH-Low Insertion Peptide (pHLIP) is a membrane-active peptide that spontaneously folds into a transmembrane α-helix upon acidification. This activity enables pHLIP to potentially act as a vector for drugs related to diseases characterized by acidosis such as cancer or heart ischemia. Presently, due to aggregation-based effects, formulations of pHLIP are only viable at near-μM concentrations. In addition, since most of pHLIP's measurable qualities involve a membrane, probing the details of pHLIP in the interstitial region is difficult. In attempts to shed light on these issues, we performed constant pH molecular dynamics simulations on pHLIP as well as P20G, a variant with increased helicity, in solution at 0 and 150 mM NaCl over a broad range of pHs. In general, the addition of ions reduced the effective pKa of the acidic residues in pHLIP. P20G exhibits a higher helicity than pHLIP in general and is more compact than pHLIP at pH values under 4. In terms of charge effects, sodium cations localized predominantly to the C-terminus of the peptide with a high density of acidic residues. Additionally, the salt bridge between R11 and D14 is by far the most favored and particularly so with pHLIP at 150 mM NaCl. We expect that this approach will be a valuable tool to screen variants of pHLIP for favorable properties in solution, an aspect of pHLIP design that to this point has largely been neglected.
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Affiliation(s)
- Nicolas Frazee
- C. Eugene Bennett Department of Chemistry, West Virginia University, Morgantown, West Virginia, USA
| | - Blake Mertz
- C. Eugene Bennett Department of Chemistry, West Virginia University, WVU Cancer Institute, Morgantown, West Virginia, USA
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5
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Deng J, Cui Q. Reverse Protonation of Buried Ion-Pairs in Staphylococcal Nuclease Mutants. J Chem Theory Comput 2021; 17:4550-4563. [PMID: 34143626 DOI: 10.1021/acs.jctc.1c00355] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/24/2023]
Abstract
Although buried titratable residues in protein cavities are often of major functional importance, it is generally challenging to understand their properties such as the ionization state and factors of stabilization based on experimental studies alone. A specific set of examples involve buried Glu-Lys pairs in a series of variants of Staphylococcal nuclease, for which recent structural and thermodynamic studies appeared to suggest that both the stability and the ionization state of the buried Glu-Lys pair are sensitive to its orientation (i.e., Glu23-Lys36 vs Lys23-Glu36). To further clarify the situation, especially ionization states of the buried Glu-Lys pairs, we have conducted extensive molecular dynamics simulations and free energy computations. Microsecond molecular dynamics simulations show that the hydration level of the cavity depends on the orientation of the buried ion-pair therein as well as its ionization state; free energy simulations recapitulate the relative stability of Glu23-Lys36 (EK) vs Lys23-Glu36 (KE) mutants measured experimentally, although the difference is similar in magnitude regardless of the ionization state of the Glu-Lys pair. A complementary set of free energy simulations strongly suggests that, in contrast to the original suggestion in the experimental analysis, the Glu and Lys residues prefer to adopt their charge-neutral rather than the ionized states. This result is consistent with the low dielectric constant computed for water in the cavity, which makes it difficult for the protein cavity to stabilize a pair of charged Glu-Lys residues, even with water penetration. The current study highlights the role of free energy simulations in understanding the ionization state of buried titratable residues and the relevant energetic contributions, forming the basis for the rational design of buried charge networks in proteins.
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Affiliation(s)
- Jiahua Deng
- Department of Chemistry, Boston University, 590 Commonwealth Avenue, Boston, Massachusetts 02215, United States
| | - Qiang Cui
- Departments of Chemistry, Physics, and Biomedical Engineering, Boston University, 590 Commonwealth Avenue, Boston, Massachusetts 02215, United States
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6
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Sarkar A, Roitberg AE. pH-Dependent Conformational Changes Lead to a Highly Shifted p Ka for a Buried Glutamic Acid Mutant of SNase. J Phys Chem B 2020; 124:11072-11080. [PMID: 33259714 DOI: 10.1021/acs.jpcb.0c07136] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Ionizable residues are rarely present in the hydrophobic interior of proteins, but when they are, they play important roles in biological processes such as energy transduction and enzyme catalysis. Internal ionizable residues have anomalous experimental pKa values with respect to their pKa in bulk water. This work investigates the atomistic cause of the highly shifted pKa of the internal Glu23 in the artificially mutated variant V23E of Staphylococcal Nuclease (SNase) using pH replica exchange molecular dynamics (pH-REMD) simulations. The pKa of Glu23 obtained from our calculations is 6.55, which is elevated with respect to the glutamate pKa of 4.40 in bulk water. The calculated value is close to the experimental pKa of 7.10. Our simulations show that the highly shifted pKa of Glu23 is the product of a pH-dependent conformational change, which has been observed experimentally and also seen in our simulations. We carry out an analysis of this pH-dependent conformational change in response to the protonation state change of Glu23. Using a four-state thermodynamic model, we estimate the two conformation-specific pKa values of Glu23 and describe the coupling between the conformational and ionization equilibria.
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Affiliation(s)
- Ankita Sarkar
- Department of Physics, University of Florida, Gainesville, Florida 32611, United States
| | - Adrian E Roitberg
- Department of Chemistry, University of Florida, Gainesville, Florida 32611, United States
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7
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Harris RC, Liu R, Shen J. Predicting Reactive Cysteines with Implicit-Solvent-Based Continuous Constant pH Molecular Dynamics in Amber. J Chem Theory Comput 2020; 16:3689-3698. [PMID: 32330035 PMCID: PMC7772776 DOI: 10.1021/acs.jctc.0c00258] [Citation(s) in RCA: 21] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022]
Abstract
Cysteines existing in the deprotonated thiolate form or having a tendency to become deprotonated are important players in enzymatic and cellular redox functions and frequently exploited in covalent drug design; however, most computational studies assume cysteines as protonated. Thus, developing an efficient tool that can make accurate and reliable predictions of cysteine protonation states is timely needed. We recently implemented a generalized Born (GB) based continuous constant pH molecular dynamics (CpHMD) method in Amber for protein pKa calculations on CPUs and GPUs. Here we benchmark the performance of GB-CpHMD for predictions of cysteine pKa's and reactivities using a data set of 24 proteins with both down- and upshifted cysteine pKa's. We found that 10 ns single-pH or 4 ns replica-exchange CpHMD titrations gave root-mean-square errors of 1.2-1.3 and correlation coefficients of 0.8-0.9 with respect to experiment. The accuracy of predicting thiolates or reactive cysteines at physiological pH with single-pH titrations is 86 or 81% with a precision of 100 or 90%, respectively. This performance well surpasses the traditional structure-based methods, particularly a widely used empirical pKa tool that gives an accuracy less than 50%. We discuss simulation convergence, dependence on starting structures, common determinants of the pKa downshifts and upshifts, and the origin of the discrepancies from the structure-based calculations. Our work suggests that CpHMD titrations can be performed on a desktop computer equipped with a single GPU card to predict cysteine protonation states for a variety of applications, from understanding biological functions to covalent drug design.
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Affiliation(s)
- Robert C Harris
- Department of Pharmaceutical Sciences, University of Maryland School of Pharmacy, Baltimore, Maryland 21201, United States
| | - Ruibin Liu
- ComputChem LLC, Baltimore, Maryland 21202, United States
| | - Jana Shen
- Department of Pharmaceutical Sciences, University of Maryland School of Pharmacy, Baltimore, Maryland 21201, United States
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8
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M2 amphipathic helices facilitate pH-dependent conformational transition in influenza A virus. Proc Natl Acad Sci U S A 2020; 117:3583-3591. [PMID: 32015120 DOI: 10.1073/pnas.1913385117] [Citation(s) in RCA: 17] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/08/2023] Open
Abstract
The matrix-2 (M2) protein from influenza A virus is a tetrameric, integral transmembrane (TM) protein that plays a vital role in viral replication by proton flux into the virus. The His37 tetrad is a pH sensor in the center of the M2 TM helix that activates the channel in response to the low endosomal pH. M2 consists of different regions that are believed to be involved in membrane targeting, packaging, nucleocapsid binding, and proton transport. Although M2 has been the target of many experimental and theoretical studies that have led to significant insights into its structure and function under differing conditions, the main mechanism of proton transport, its conformational dynamics, and the role of the amphipathic helices (AHs) on proton conductance remain elusive. To this end, we have applied explicit solvent constant pH molecular dynamics using the multisite λ-dynamics approach (CpHMDMSλD) to investigate the buried ionizable residues comprehensively and to elucidate their effect on the conformational transition. Our model recapitulates the pH-dependent conformational transition of M2 from closed to open state when the AH domain is included in the M2 construct, revealing the role of the amphipathic helices on this transition and shedding light on the proton-transport mechanism. This work demonstrates the importance of including the amphipathic helices in future experimental and theoretical studies of ion channels. Finally, our work shows that explicit solvent CpHMDMSλD provides a realistic pH-dependent model for membrane proteins.
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9
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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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10
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Haynes EP, Rajendran M, Henning CK, Mishra A, Lyon AM, Tantama M. Quantifying Acute Fuel and Respiration Dependent pH Homeostasis in Live Cells Using the mCherryTYG Mutant as a Fluorescence Lifetime Sensor. Anal Chem 2019; 91:8466-8475. [PMID: 31247720 PMCID: PMC6623984 DOI: 10.1021/acs.analchem.9b01562] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022]
Abstract
Intracellular pH plays a key role in physiology, and its measurement in living specimens remains a crucial task in biology. Fluorescent protein-based pH sensors have gained widespread use, but there is limited spectral diversity for multicolor detection, and it remains a challenge to measure absolute pH values. Here we demonstrate that mCherryTYG is an excellent fluorescence lifetime pH sensor that significantly expands the modalities available for pH quantification in live cells. We first report the 1.09 Å X-ray crystal structure of mCherryTYG, exhibiting a fully matured chromophore. We next determine that it has an extraordinarily large dynamic range with a 2 ns lifetime change from pH 5.5 to 9.0. Critically, we find that the sensor maintains a p Ka of 6.8 independent of environment, whether as the purified protein in solution or expressed in live cells. Furthermore, the lifetime measurements are robustly independent of total fluorescence intensity and scatter. We demonstrate that mCherryTYG is a highly effective sensor using time-resolved fluorescence spectroscopy on live-cell suspensions, which has been previously overlooked as an easily accessible approach for quantifying intracellular pH. As a red fluorescent sensor, we also demonstrate that mCherryTYG is spectrally compatible with the ATeam sensor and EGFP for simultaneous dual-color measurements of intracellular pH, ATP, and extracellular pH. In a proof-of-concept, we quantify acute respiration-dependent pH homeostasis that exhibits a stoichiometric relationship with the ATP-generating capacity of the carbon fuel choice in E. coli. Broadly speaking, our work presents a previously unemployed methodology that will greatly facilitate continuous pH quantification.
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Affiliation(s)
- Emily P. Haynes
- Department of Chemistry, Purdue University, 560 Oval Drive, Box 68, West Lafayette, IN 47907, USA
| | - Megha Rajendran
- Department of Chemistry, Purdue University, 560 Oval Drive, Box 68, West Lafayette, IN 47907, USA
- Institute for Integrative Neuroscience, Purdue University, 560 Oval Drive, Box 68, West Lafayette, IN 47907, USA
| | | | | | - Angeline M. Lyon
- Department of Chemistry, Purdue University, 560 Oval Drive, Box 68, West Lafayette, IN 47907, USA
- Institute of Inflammation, Immunology, and Infectious Disease, Purdue University, 560 Oval Drive, Box 68, West Lafayette, IN 47907, USA
- Department of Biological Sciences, Purdue University, 560 Oval Drive, Box 68, West Lafayette, IN 47907, USA
| | - Mathew Tantama
- Department of Chemistry, Purdue University, 560 Oval Drive, Box 68, West Lafayette, IN 47907, USA
- Institute for Integrative Neuroscience, Purdue University, 560 Oval Drive, Box 68, West Lafayette, IN 47907, USA
- Institute of Inflammation, Immunology, and Infectious Disease, Purdue University, 560 Oval Drive, Box 68, West Lafayette, IN 47907, USA
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11
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Sarkar A, Gupta PL, Roitberg AE. pH-Dependent Conformational Changes Due to Ionizable Residues in a Hydrophobic Protein Interior: The Study of L25K and L125K Variants of SNase. J Phys Chem B 2019; 123:5742-5754. [DOI: 10.1021/acs.jpcb.9b03816] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022]
Affiliation(s)
- Ankita Sarkar
- Department of Physics, University of Florida, Gainesville, Florida 32611, United States
| | - Pancham Lal Gupta
- Department of Chemistry, University of Florida, Gainesville, Florida 32603, United States
| | - Adrian E. Roitberg
- Department of Chemistry, University of Florida, Gainesville, Florida 32603, United States
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12
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Abstract
The aggregation of amyloid fibrils can lead to various diseases including Alzheimer's, Parkinson's disease, and transmissible spongiform encephalopathy. Amyloid fibrils can develop from a variety of proteins in the body as they misfold into a primarily β-sheet structure and aggregate. Human lysozyme has been shown to have far reaching effects in the human health-a homologous enzyme, hen egg-white lysozyme, has been shown to denature to a primarily β-sheet structure at low pH and high alcohol content solution. We have studied these systems in atomic-level detail with a combination of constant pH and microsecond long molecular dynamics simulation in explicit solvent, which cumulatively total over 10 μs of simulation time. These studies have allowed us to determine two potential unfolding pathways depending on the protonation state of a key glutamic acid residue as well as the effect of solution dynamics and pH on the unfolding process.
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Affiliation(s)
- Alice R. Walker
- Department of Chemistry, University of North Texas, Denton, TX 76201, USA
| | - Nikhil Baddam
- Department of Chemistry, Wayne State University, Detroit, MI 48202, USA
| | - G. Andrés Cisneros
- Department of Chemistry, University of North Texas, Denton, TX 76201, USA
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13
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Zhang Y, Zhang H, Zheng Q. A unique activation-promotion mechanism of the influenza B M2 proton channel uncovered by multiscale simulations. Phys Chem Chem Phys 2019; 21:2984-2991. [PMID: 30672572 DOI: 10.1039/c9cp00130a] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/25/2022]
Abstract
The influenza B M2 protein (BM2) forms an acid-activated proton channel that is important for the virus's lifecycle. Despite extensive research efforts, the detailed activation mechanism of the BM2 proton channel is often elusive. Herein a pH-regulated mechanism of the BM2TM domain has been systematically characterized using multiscale computer simulations, including classical molecular dynamics, constant pH molecular dynamics (CpHMD) and quantum mechanics/molecular mechanics (QM/MM) approaches. Our simulations reveal a pH-dependent conformational switch from the C-terminal closed to the C-terminal open conformers, and provide the free energy of conformational activation coupled to the titration of the His19 tetrad. Importantly, our results confirm the coupling titration between the His19 tetrad and His27 tetrad, and identify that the full-cationic state (His2744+) dominates at the low pH (the His19 tetrad at +2, +3 and +4 charge states). Our QM/MM simulations indicate that the second titratable histidine, His27, could further promote the BM2 acid activation and speed up proton dissociation from the HxxxW motif, thus facilitating proton conduction by BM2. Taken together, a unique "activation-promotion mechanism" about the BM2 proton channel is proposed, and these results may be helpful for the understanding of other similar proton channels and the development of BM2 inhibitors.
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Affiliation(s)
- Yulai Zhang
- Laboratory of Theoretical and Computational Chemistry, Institute of Theoretical Chemistry, International Joint Research Laboratory of Nano-Micro Architecture Chemistry, Jilin University, Changchun 130023, People's Republic of China.
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14
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Damjanovic A, Miller BT, Okur A, Brooks BR. Reservoir pH replica exchange. J Chem Phys 2018; 149:072321. [PMID: 30134701 PMCID: PMC6005788 DOI: 10.1063/1.5027413] [Citation(s) in RCA: 19] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/01/2018] [Accepted: 05/30/2018] [Indexed: 11/15/2022] Open
Abstract
We present the reservoir pH replica exchange (R-pH-REM) method for constant pH simulations. The R-pH-REM method consists of a two-step procedure; the first step involves generation of one or more reservoirs of conformations. Each reservoir is obtained from a standard or enhanced molecular dynamics simulation with a constrained (fixed) protonation state. In the second step, fixed charge constraints are relaxed, as the structures from one or more reservoirs are periodically injected into a constant pH or a pH-replica exchange (pH-REM) simulation. The benefit of this two-step process is that the computationally intensive part of conformational search can be decoupled from constant pH simulations, and various techniques for enhanced conformational sampling can be applied without the need to integrate such techniques into the pH-REM framework. Simulations on blocked Lys, KK, and KAAE peptides were used to demonstrate an agreement between pH-REM and R-pH-REM simulations. While the reservoir simulations are not needed for these small test systems, the real need arises in cases when ionizable molecules can sample two or more conformations separated by a large energy barrier, such that adequate sampling is not achieved on a time scale of standard constant pH simulations. Such problems might be encountered in protein systems that exploit conformational transitions for function. A hypothetical case is studied, a small molecule with a large torsional barrier; while results of pH-REM simulations depend on the starting structure, R-pH-REM calculations on this model system are in excellent agreement with a theoretical model.
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Affiliation(s)
- Ana Damjanovic
- Author to whom correspondence should be addressed: . Tel.: (410) 516-5390. FAX: (410) 516-4118
| | - Benjamin T. Miller
- Laboratory of Computational Biology, National Heart, Lung, and Blood Institute, National Institutes of Health, Bethesda, Maryland 20892-5690, USA
| | - Asim Okur
- Laboratory of Computational Biology, National Heart, Lung, and Blood Institute, National Institutes of Health, Bethesda, Maryland 20892-5690, USA
| | - Bernard R. Brooks
- Laboratory of Computational Biology, National Heart, Lung, and Blood Institute, National Institutes of Health, Bethesda, Maryland 20892-5690, USA
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15
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Gueto-Tettay C, Martinez-Consuegra A, Pelaez-Bedoya L, Drosos-Ramirez JC. G-score: A function to solve the puzzle of modeling the protonation states of β-secretase binding pocket. J Mol Graph Model 2018; 85:1-12. [PMID: 30053756 DOI: 10.1016/j.jmgm.2018.07.008] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/17/2018] [Revised: 07/13/2018] [Accepted: 07/16/2018] [Indexed: 10/28/2022]
Abstract
The population density concept has emerged as a proposal for the analysis of molecular dynamics results, the key characteristic of population density is the evaluation of the simultaneous occurrence of a set of relevant parameters for a system. However, despite its statistical strength, selection of the tolerance level for the comparison of different models may appear as arbitrary. This work introduces the G-score, a function which summarizes and categorizes the results of population density analysis. Additionally, it incorporates parameters based on rmsd and dihedral angles, besides the protein-protein and protein-ligand interatomic distances conventionally used, which complement each other to provide a better description of the behavior of the system. These newly-proposed tools were applied to determine the most probable protonation state of the aspartic dyad of BACE1, Asp93 and Asp289, in the presence of three types of transition state inhibitors namely: reduced amides, tertiary carbinamines and hydroxyethylamines. The results show a full agreement between G-score values and population density charts, with the advantage of allowing a quick and direct comparison among all the considered models. We anticipate that the simplicity of calculating the parameters employed in this study will permit the extensive use of population density and the G-score for other molecular systems.
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Affiliation(s)
- Carlos Gueto-Tettay
- Grupo de Química Bioorgánica, Facultad de Ciencias Exactas y Naturales, Universidad de Cartagena, Campus San Pablo, 130015, Colombia; Lund University, Faculty of Medicine, Department of Clinical Sciences Lund, Division of Infection Medicine, Lund, Sweden.
| | - Alejandro Martinez-Consuegra
- Grupo de Química Bioorgánica, Facultad de Ciencias Exactas y Naturales, Universidad de Cartagena, Campus San Pablo, 130015, Colombia
| | - Luis Pelaez-Bedoya
- Grupo de Química Bioorgánica, Facultad de Ciencias Exactas y Naturales, Universidad de Cartagena, Campus San Pablo, 130015, Colombia
| | - Juan Carlos Drosos-Ramirez
- Grupo de Química Bioorgánica, Facultad de Ciencias Exactas y Naturales, Universidad de Cartagena, Campus San Pablo, 130015, Colombia.
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16
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Li Z, Zhang X, Wang Q, Li C, Zhang N, Zhang X, Xu B, Ma B, Schrader TE, Coates L, Kovalevsky A, Huang Y, Wan Q. Understanding the pH-Dependent Reaction Mechanism of a Glycoside Hydrolase Using High-Resolution X-ray and Neutron Crystallography. ACS Catal 2018. [DOI: 10.1021/acscatal.8b01472] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- Zhihong Li
- College of Science, Nanjing Agricultural University, Nanjing 210095, People’s Republic of China
| | - Xiaoshuai Zhang
- College of Science, Nanjing Agricultural University, Nanjing 210095, People’s Republic of China
| | - Qingqing Wang
- College of Science, Nanjing Agricultural University, Nanjing 210095, People’s Republic of China
| | - Chunran Li
- College of Science, Nanjing Agricultural University, Nanjing 210095, People’s Republic of China
| | - Nianying Zhang
- College of Science, Nanjing Agricultural University, Nanjing 210095, People’s Republic of China
| | - Xinkai Zhang
- College of Science, Nanjing Agricultural University, Nanjing 210095, People’s Republic of China
| | - Birui Xu
- College of Science, Nanjing Agricultural University, Nanjing 210095, People’s Republic of China
| | - Baoliang Ma
- College of Science, Nanjing Agricultural University, Nanjing 210095, People’s Republic of China
| | - Tobias E. Schrader
- Jülich Centre for Neutron Science at Heinz Maier-Leibnitz Zentrum, Forschungszentrum Jülich GmbH, Garching 85747, Germany
| | - Leighton Coates
- Neutron Scattering Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, United States
| | - Andrey Kovalevsky
- Neutron Scattering Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, United States
| | - Yandong Huang
- College of Computer Engineering, Jimei University, Xiamen 361021, People’s Republic of China
| | - Qun Wan
- College of Science, Nanjing Agricultural University, Nanjing 210095, People’s Republic of China
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17
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Wu X, Brooks BR. Hydronium Ions Accompanying Buried Acidic Residues Lead to High Apparent Dielectric Constants in the Interior of Proteins. J Phys Chem B 2018; 122:6215-6223. [PMID: 29771522 DOI: 10.1021/acs.jpcb.8b04584] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
Abstract
Internal ionizable groups are known to play important roles in protein functions. A mystery that has attracted decades of extensive experimental and theoretical studies is the apparent dielectric constants experienced by buried ionizable groups, which are much higher than values expected for protein interiors. Many interpretations have been proposed, such as water penetration, conformational relaxation, local unfolding, protein intrinsic backbone fluctuations, etc. However, these interpretations conflict with many experimental observations. The virtual mixture of multiple states (VMMS) simulation method developed in our lab provides a direct approach for studying the equilibrium of multiple chemical states and can monitor p Ka values along simulation trajectories. Through VMMS simulations of staphylococcal nuclease (SNase) variants with internal Asp or Glu residues, we discovered that cations were attracted to buried deprotonated acidic groups and the presence of the nearby cations were essential to reproduce experimentally measured p Ka values. This finding, combined with structural analysis and validation simulations, suggests that the proton released from a deprotonation process stays near the deprotonated group inside proteins, possibly in the form of a hydronium ion. The existence of a proton near a buried charge has many implications in our understanding of protein functions.
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Affiliation(s)
- Xiongwu Wu
- Laboratory of Computational Biology, National Heart, Lung, and Blood Institute (NHLBI) , National Institutes of Health (NIH) , Bethesda , Maryland 20892 , United States
| | - Bernard R Brooks
- Laboratory of Computational Biology, National Heart, Lung, and Blood Institute (NHLBI) , National Institutes of Health (NIH) , Bethesda , Maryland 20892 , United States
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18
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Kougentakis CM, Grasso EM, Robinson AC, Caro JA, Schlessman JL, Majumdar A, García-Moreno E B. Anomalous Properties of Lys Residues Buried in the Hydrophobic Interior of a Protein Revealed with 15N-Detect NMR Spectroscopy. J Phys Chem Lett 2018; 9:383-387. [PMID: 29266956 DOI: 10.1021/acs.jpclett.7b02668] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/07/2023]
Abstract
Ionizable residues buried in hydrophobic environments in proteins are essential for many fundamental biochemical processes. These residues titrate with anomalous pKa values that are challenging to reproduce with structure-based calculations owing to the conformational reorganization coupled to their ionization. Detailed characterization of this conformational reorganization is of interest; unfortunately, the properties of buried Lys residues are difficult to study experimentally. Here we demonstrate the utility of 15N NMR spectroscopy to gain insight into the protonation state, state of hydration and conformational dynamics of the Nζ amino group of buried Lys residues. The experiments were applied to five variants of staphylococcal nuclease, with internal Lys residues that titrate with pKa values ranging from 6.2 to 8.1. Direct detection of buried Lys residues with these NMR spectroscopy methods will enable correlation between thermodynamic and structural data as well as unprecedented examination of how conformational transitions coupled to their ionization affect their pKa values.
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Affiliation(s)
| | | | | | | | - Jamie L Schlessman
- Chemistry Department, United States Naval Academy , 572M Holloway Rd MS 9B, Annapolis, Maryland 21402, United States
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19
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Zhou HX, Pang X. Electrostatic Interactions in Protein Structure, Folding, Binding, and Condensation. Chem Rev 2018; 118:1691-1741. [PMID: 29319301 DOI: 10.1021/acs.chemrev.7b00305] [Citation(s) in RCA: 477] [Impact Index Per Article: 79.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
Charged and polar groups, through forming ion pairs, hydrogen bonds, and other less specific electrostatic interactions, impart important properties to proteins. Modulation of the charges on the amino acids, e.g., by pH and by phosphorylation and dephosphorylation, have significant effects such as protein denaturation and switch-like response of signal transduction networks. This review aims to present a unifying theme among the various effects of protein charges and polar groups. Simple models will be used to illustrate basic ideas about electrostatic interactions in proteins, and these ideas in turn will be used to elucidate the roles of electrostatic interactions in protein structure, folding, binding, condensation, and related biological functions. In particular, we will examine how charged side chains are spatially distributed in various types of proteins and how electrostatic interactions affect thermodynamic and kinetic properties of proteins. Our hope is to capture both important historical developments and recent experimental and theoretical advances in quantifying electrostatic contributions of proteins.
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Affiliation(s)
- Huan-Xiang Zhou
- Department of Chemistry and Department of Physics, University of Illinois at Chicago , Chicago, Illinois 60607, United States.,Department of Physics and Institute of Molecular Biophysics, Florida State University , Tallahassee, Florida 32306, United States
| | - Xiaodong Pang
- Department of Physics and Institute of Molecular Biophysics, Florida State University , Tallahassee, Florida 32306, United States
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20
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Lošdorfer Božič A, Podgornik R. pH Dependence of Charge Multipole Moments in Proteins. Biophys J 2017; 113:1454-1465. [PMID: 28978439 DOI: 10.1016/j.bpj.2017.08.017] [Citation(s) in RCA: 40] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/30/2017] [Revised: 08/10/2017] [Accepted: 08/11/2017] [Indexed: 11/26/2022] Open
Abstract
Electrostatic interactions play a fundamental role in the structure and function of proteins. Due to ionizable amino acid residues present on the solvent-exposed surfaces of proteins, the protein charge is not constant but varies with the changes in the environment-most notably, the pH of the surrounding solution. We study the effects of pH on the charge of four globular proteins by expanding their surface charge distributions in terms of multipoles. The detailed representation of the charges on the proteins is in this way replaced by the magnitudes and orientations of the multipole moments of varying order. Focusing on the three lowest-order multipoles-the total charge, dipole, and quadrupole moment-we show that the value of pH influences not only their magnitudes, but more notably and importantly also the spatial orientation of their principal axes. Our findings imply important consequences for the study of protein-protein interactions and the assembly of both proteinaceous shells and patchy colloids with dissociable charge groups.
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Affiliation(s)
| | - Rudolf Podgornik
- Department of Theoretical Physics, Jožef Stefan Institute, Ljubljana, Slovenia; Department of Physics, Faculty of Mathematics and Physics, University of Ljubljana, Ljubljana, Slovenia
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21
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Abstract
An important limitation of standard classical molecular dynamics simulations is the inability to make or break chemical bonds. This restricts severely our ability to study processes that involve even the simplest of chemical reactions, the transfer of a proton. Existing approaches for allowing proton transfer in the context of classical mechanics are rather cumbersome and have not achieved widespread use and routine status. Here we reconsider the combination of molecular dynamics with periodic stochastic proton hops. To ensure computational efficiency, we propose a non-Boltzmann acceptance criterion that is heuristically adjusted to maintain the correct or desirable thermodynamic equilibria between different protonation states and proton transfer rates. Parameters are proposed for hydronium, Asp, Glu, and His. The algorithm is implemented in the program CHARMM and tested on proton diffusion in bulk water and carbon nanotubes and on proton conductance in the gramicidin A channel. Using hopping parameters determined from proton diffusion in bulk water, the model reproduces the enhanced proton diffusivity in carbon nanotubes and gives a reasonable estimate of the proton conductance in gramicidin A.
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Affiliation(s)
- Themis Lazaridis
- Department of Chemistry, City College of New York/CUNY , 160 Convent Avenue, New York, New York 10031, United States.,Graduate Programs in Chemistry, Biochemistry & Physics, Graduate Center, City University of New York , 365 Fifth Ave, New York, New York 10016, United States
| | - Gerhard Hummer
- Department of Theoretical Biophysics, Max Planck Institute of Biophysics , Max-von-Laue Strasse 3, 60438 Frankfurt am Main, Germany
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22
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Peck MT, Ortega G, De Luca-Johnson JN, Schlessman JL, Robinson AC, García-Moreno E B. Local Backbone Flexibility as a Determinant of the Apparent pKa Values of Buried Ionizable Groups in Proteins. Biochemistry 2017; 56:5338-5346. [DOI: 10.1021/acs.biochem.7b00678] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/22/2023]
Affiliation(s)
- Meredith T. Peck
- Department
of Biophysics, Johns Hopkins University, Baltimore, Maryland 21218, United States
| | - Gabriel Ortega
- Structural
Biology Unit, CIC bioGUNE, Bizkaia Technology Park Ed. 800, 48160 Derio, Spain
- Department
of Chemistry and Biochemistry, University of California, Santa Barbara, California 93106, United States
| | | | - Jamie L. Schlessman
- Chemistry
Department, U.S. Naval Academy, Annapolis, Maryland 21402, United States
| | - Aaron C. Robinson
- Department
of Biophysics, Johns Hopkins University, Baltimore, Maryland 21218, United States
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23
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Electric-Field-Induced Protein Translocation via a Conformational Transition in SecDF: An MD Study. Biophys J 2017. [PMID: 28636909 DOI: 10.1016/j.bpj.2017.04.034] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
SecDF is an important component of the Sec protein translocation machinery embedded in the bacterial membrane, which is associated with many functions, such as stabilizing other Sec translocon components within the membrane, maintaining the transmembrane (TM) potential, and facilitating the ATP-independent stage of the translocation mechanism. Related studies suggest that SecDF undergoes functionally important conformational changes that involve mainly its P1-head domain and that these changes are coupled with the proton motive force (Δp). However, there still is not a clear understanding of how SecDF functions, its exact role in the translocation machinery, and how its function is related to Δp. Here, using all-atom molecular dynamics simulations combined with umbrella sampling, we study the P1-head conformational change and how it is coupled to the proton motive force. We report potentials of mean force along a root-mean-square-distance-based reaction coordinate obtained in the presence and absence of the TM electrical potential. Our results show that the interaction of the P1 domain dipole moment with the TM electrical field considerably lowers the free-energy barrier in the direction of F-form to I-form transition.
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24
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Jo S, Cheng X, Lee J, Kim S, Park SJ, Patel DS, Beaven AH, Lee KI, Rui H, Park S, Lee HS, Roux B, MacKerell AD, Klauda JB, Qi Y, Im W. CHARMM-GUI 10 years for biomolecular modeling and simulation. J Comput Chem 2017; 38:1114-1124. [PMID: 27862047 PMCID: PMC5403596 DOI: 10.1002/jcc.24660] [Citation(s) in RCA: 186] [Impact Index Per Article: 26.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/13/2016] [Revised: 10/04/2016] [Accepted: 10/18/2016] [Indexed: 12/16/2022]
Abstract
CHARMM-GUI, http://www.charmm-gui.org, is a web-based graphical user interface that prepares complex biomolecular systems for molecular simulations. CHARMM-GUI creates input files for a number of programs including CHARMM, NAMD, GROMACS, AMBER, GENESIS, LAMMPS, Desmond, OpenMM, and CHARMM/OpenMM. Since its original development in 2006, CHARMM-GUI has been widely adopted for various purposes and now contains a number of different modules designed to set up a broad range of simulations: (1) PDB Reader & Manipulator, Glycan Reader, and Ligand Reader & Modeler for reading and modifying molecules; (2) Quick MD Simulator, Membrane Builder, Nanodisc Builder, HMMM Builder, Monolayer Builder, Micelle Builder, and Hex Phase Builder for building all-atom simulation systems in various environments; (3) PACE CG Builder and Martini Maker for building coarse-grained simulation systems; (4) DEER Facilitator and MDFF/xMDFF Utilizer for experimentally guided simulations; (5) Implicit Solvent Modeler, PBEQ-Solver, and GCMC/BD Ion Simulator for implicit solvent related calculations; (6) Ligand Binder for ligand solvation and binding free energy simulations; and (7) Drude Prepper for preparation of simulations with the CHARMM Drude polarizable force field. Recently, new modules have been integrated into CHARMM-GUI, such as Glycolipid Modeler for generation of various glycolipid structures, and LPS Modeler for generation of lipopolysaccharide structures from various Gram-negative bacteria. These new features together with existing modules are expected to facilitate advanced molecular modeling and simulation thereby leading to an improved understanding of the structure and dynamics of complex biomolecular systems. Here, we briefly review these capabilities and discuss potential future directions in the CHARMM-GUI development project. © 2016 Wiley Periodicals, Inc.
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Affiliation(s)
- Sunhwan Jo
- Leadership Computing Facility, Argonne National Laboratory, 9700 Cass Ave, Argonne, Illinois
| | - Xi Cheng
- Drug Discovery and Design Center, State Key Laboratory of Drug Research, Shanghai Institute of Materia Medica Chinese Academy of Sciences, 555 Zuchongzhi Road, Pudong, Shanghai, 201203, China
| | - Jumin Lee
- Department of Biological Sciences and Bioengineering Program, Lehigh University, Pennsylvania
| | - Seonghoon Kim
- Department of Biological Sciences and Bioengineering Program, Lehigh University, Pennsylvania
| | - Sang-Jun Park
- Department of Biological Sciences and Bioengineering Program, Lehigh University, Pennsylvania
| | - Dhilon S Patel
- Department of Biological Sciences and Bioengineering Program, Lehigh University, Pennsylvania
| | - Andrew H Beaven
- Department of Chemistry, The University of Kansas, Lawrence, Kansas
| | - Kyu Il Lee
- Department of Biological Sciences and Bioengineering Program, Lehigh University, Pennsylvania
| | - Huan Rui
- Department of Biochemistry and Molecular Biology, The University of Chicago, Chicago, Illinois
| | - Soohyung Park
- Department of Biological Sciences and Bioengineering Program, Lehigh University, Pennsylvania
| | - Hui Sun Lee
- Department of Biological Sciences and Bioengineering Program, Lehigh University, Pennsylvania
| | - Benoît Roux
- Department of Biochemistry and Molecular Biology, The University of Chicago, Chicago, Illinois
| | - Alexander D MacKerell
- Department of Pharmaceutical Sciences School of Pharmacy, University of Maryland, Baltimore, Maryland
| | - Jeffrey B Klauda
- Department of Chemical and Biomolecular Engineering and the Biophysics Program, University of Maryland College Park, Maryland
| | - Yifei Qi
- Department of Biological Sciences and Bioengineering Program, Lehigh University, Pennsylvania
| | - Wonpil Im
- Department of Biological Sciences and Bioengineering Program, Lehigh University, Pennsylvania
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25
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Robinson AC, Majumdar A, Schlessman JL, García-Moreno E B. Charges in Hydrophobic Environments: A Strategy for Identifying Alternative States in Proteins. Biochemistry 2016; 56:212-218. [DOI: 10.1021/acs.biochem.6b00843] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022]
Affiliation(s)
| | | | - Jamie L. Schlessman
- Chemistry
Department, United States Naval Academy, 572M Holloway Rd MS 9B, Annapolis, Maryland 21402, United States
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26
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Zheng Y, Cui Q. Microscopic mechanisms that govern the titration response and pK a values of buried residues in staphylococcal nuclease mutants. Proteins 2016; 85:268-281. [PMID: 27862310 DOI: 10.1002/prot.25213] [Citation(s) in RCA: 25] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/16/2016] [Revised: 10/19/2016] [Accepted: 10/28/2016] [Indexed: 01/09/2023]
Abstract
To probe the microscopic mechanisms that govern the titration behavior of buried ionizable groups, microsecond explicit solvent molecular dynamics simulations are carried out for several mutants of Staphylococcal nuclease using both fixed charge and polarizable force fields. While the ionization of Asp 66, Glu 66, and Lys 125 lead to enhanced structural fluctuations and partial unfolding of adjacent α-helical regions, the ionization of Lys 25 causes local unfolding of adjacent β sheets. Using the sampled conformational ensembles, good agreement with experimental pKa values is obtained with Poisson-Boltzmann calculations using a protein dielectric constant of 2-4 for V66D/E; slightly larger dielectric constants are needed for Lys mutants especially L25K, suggesting that structural responses beyond microseconds are involved in ionization of Lys 25. Overall, the set of unbiased simulations provides insights into the spatial and temporal scales of protein and solvent motions that dictate the diverse titration behaviors of buried protein residues. Proteins 2017; 85:268-281. © 2016 Wiley Periodicals, Inc.
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Affiliation(s)
- Yuqing Zheng
- Graduate Program in Biophysics, University of Wisconsin-Madison, 1525 Linden Drive, Madison, Wisconsin, 53706
| | - Qiang Cui
- Department of Chemistry and Theoretical Chemistry Institute, University of Wisconsin-Madison, 1101 University Avenue, Madison, Wisconsin, 53706
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27
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Panahi A, Bandara A, Pantelopulos GA, Dominguez L, Straub JE. Specific Binding of Cholesterol to C99 Domain of Amyloid Precursor Protein Depends Critically on Charge State of Protein. J Phys Chem Lett 2016; 7:3535-41. [PMID: 27525349 PMCID: PMC5293176 DOI: 10.1021/acs.jpclett.6b01624] [Citation(s) in RCA: 28] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 05/15/2023]
Abstract
Recent NMR chemical shift measurements of the 99 residue C-terminal fragment of amyloid precursor protein (APP-C99) in the presence of cholesterol provide evidence of binary complex formation between C99 and cholesterol in membrane mimetic environments. It has also been observed that the production of Aβ protein is enhanced under conditions of high cholesterol concentration. In this study, we investigated the impact of the charge state of C99 on the structure and stability of the C99-cholesterol complex. We observed that the binding of C99 to cholesterol depends critically on the charge state of Glu 693 (E22) and Asp 694 (D23). Evaluation of the pKa values of the Asp and Glu side chains suggests that these residues may be predominantly neutral in existing experimental observations of a stable C99-cholesterol complex at lower pH (characteristic of the endosomal environment), while binding is destabilized near neutral pH (characteristic of the cytoplasm). These observations suggest that specific binding of cholesterol to C99 is a sensitive function of the pH encountered in vivo, with key E22 and D23 residues serving as a "pH switch" controlling C99-cholesterol binding.
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Affiliation(s)
- Afra Panahi
- Department of Chemistry, Boston University, 590 Commonwealth Avenue, Boston, Massachusetts, 02215
| | - Asanga Bandara
- Department of Chemistry, Boston University, 590 Commonwealth Avenue, Boston, Massachusetts, 02215
| | - George A. Pantelopulos
- Department of Chemistry, Boston University, 590 Commonwealth Avenue, Boston, Massachusetts, 02215
| | - Laura Dominguez
- Biophysical Chemistry Laboratory, Physical Chemistry Department, School of Chemistry, National Autonomous University of Mexico, Mexico City, Mexico
| | - John E. Straub
- Department of Chemistry, Boston University, 590 Commonwealth Avenue, Boston, Massachusetts, 02215
- Corresponding Author:
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28
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Soares RO, Torres PHM, da Silva ML, Pascutti PG. Unraveling HIV protease flaps dynamics by Constant pH Molecular Dynamics simulations. J Struct Biol 2016; 195:216-226. [PMID: 27291071 DOI: 10.1016/j.jsb.2016.06.006] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/13/2016] [Revised: 06/08/2016] [Accepted: 06/09/2016] [Indexed: 11/15/2022]
Abstract
The active site of HIV protease (HIV-PR) is covered by two flaps. These flaps are known to be essential for the catalytic activity of the HIV-PR, but their exact conformations at the different stages of the enzymatic pathway remain subject to debate. Understanding the correct functional dynamics of the flaps might aid the development of new HIV-PR inhibitors. It is known that, the HIV-PR catalytic efficiency is pH-dependent, likely due to the influence of processes such as charge transfer and protonation/deprotonation of ionizable residues. Several Molecular Dynamics (MD) simulations have reported information about the HIV-PR flaps. However, in MD simulations the protonation of a residue is fixed and thus it is not possible to study the correlation between conformation and protonation state. To address this shortcoming, this work attempts to capture, through Constant pH Molecular Dynamics (CpHMD), the conformations of the apo, substrate-bound and inhibitor-bound HIV-PR, which differ drastically in their flap arrangements. The results show that the HIV-PR flaps conformations are defined by the protonation of the catalytic residues Asp25/Asp25' and that these residues are sensitive to pH changes. This study suggests that the catalytic aspartates can modulate the opening of the active site and substrate binding.
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Affiliation(s)
- Rosemberg O Soares
- Instituto de Biofísica Carlos Chagas Filho (IBCCF), Universidade Federal do Rio de Janeiro (UFRJ), Rio de Janeiro, Brazil; Diretoria de Metrologia Aplicada às Ciências da Vida (DIMAV), Instituto Nacional de Metrologia Qualidade e Tecnologia (INMETRO), Xerém, Brazil.
| | - Pedro H M Torres
- Instituto de Biofísica Carlos Chagas Filho (IBCCF), Universidade Federal do Rio de Janeiro (UFRJ), Rio de Janeiro, Brazil
| | - Manuela L da Silva
- Diretoria de Metrologia Aplicada às Ciências da Vida (DIMAV), Instituto Nacional de Metrologia Qualidade e Tecnologia (INMETRO), Xerém, Brazil
| | - Pedro G Pascutti
- Instituto de Biofísica Carlos Chagas Filho (IBCCF), Universidade Federal do Rio de Janeiro (UFRJ), Rio de Janeiro, Brazil; Diretoria de Metrologia Aplicada às Ciências da Vida (DIMAV), Instituto Nacional de Metrologia Qualidade e Tecnologia (INMETRO), Xerém, Brazil
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29
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Richman DE, Majumdar A, García-Moreno E B. Conformational Reorganization Coupled to the Ionization of Internal Lys Residues in Proteins. Biochemistry 2015; 54:5888-97. [PMID: 26335188 DOI: 10.1021/acs.biochem.5b00522] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023]
Abstract
Ionizable groups buried in the hydrophobic interior of proteins are essential for energy transduction and catalysis. Because the protein interior is usually neither as polar nor as polarizable as water, these groups tend to have anomalous pKa values, and their ionization tends to be coupled to conformational reorganization. To elucidate mechanisms of energy transduction in proteins, it is necessary to understand the structural determinants of the pKa values of these buried groups, including the range and character of the conformational reorganization that the ionization of these buried groups can elicit. The L25K and L125K variants of staphylococcal nuclease (SNase) were used to characterize the diverse types of structural reorganization that can be promoted by the ionization of buried groups. NMR relaxation dispersion and ZZ-exchange experiments were used to identify the locations and measure the time scales and extent of pH-dependent conformational exchange in these two proteins. The buried Lys-25 and Lys-125 residues titrate with pKa of 6.3 and 6.2, respectively. The L25K protein fluctuates between the native state and an ensemble of locally unfolded states on the 400 μs to 7 ms time scale. On the 100 to 500 ms time scale the native state exchanges with a subglobally unfolded state in which the β-barrel is partially reorganized. The equilibrium between the native state and this alternative state is highly pH dependent; at pH values below the pKa of Lys-25 the state with the partially reorganized β-barrel is the dominant state. In contrast, the L125K protein only exhibited pH-independent fluctuation in the microsecond to millisecond time scale in the region near Lys-125. The study illustrates how diverse and how localized the coupling between conformational reorganization and ionization of buried groups can be. The pH-sensitive exchange between the fully native and subglobally or locally unfolded states in time scales well into hundreds of milliseconds will challenge all computational methods for structure-based calculations of pKa values.
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Affiliation(s)
- Daniel E Richman
- Department of Biophysics and ‡Biomolecular NMR Center, Johns Hopkins University , 3400 North Charles Street, Baltimore, Maryland 21218, United States
| | - Ananya Majumdar
- Department of Biophysics and ‡Biomolecular NMR Center, Johns Hopkins University , 3400 North Charles Street, Baltimore, Maryland 21218, United States
| | - Bertrand García-Moreno E
- Department of Biophysics and ‡Biomolecular NMR Center, Johns Hopkins University , 3400 North Charles Street, Baltimore, Maryland 21218, United States
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30
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Yang M, Zhang X, Liu H, Kang H, Zhu Z, Yang W, Tan W. Stable DNA Nanomachine Based on Duplex-Triplex Transition for Ratiometric Imaging Instantaneous pH Changes in Living Cells. Anal Chem 2015; 87:5854-9. [PMID: 26016566 PMCID: PMC4928482 DOI: 10.1021/acs.analchem.5b01233] [Citation(s) in RCA: 48] [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: 04/01/2015] [Accepted: 05/27/2015] [Indexed: 02/07/2023]
Abstract
DNA nanomachines are becoming useful tools for molecular recognition, imaging, and diagnostics and have drawn gradual attention. Unfortunately, the present application of most DNA nanomachines is limited in vitro, so expanding their application in organism has become a primary focus. Hence, a novel DNA nanomachine named t-switch, based on the DNA duplex-triplex transition, is developed for monitoring the intracellular pH gradient. Our strategy is based on the DNA triplex structure containing C(+)-G-C triplets and pH-dependent Förster resonance energy transfer (FRET). Our results indicate that the t-switch is an efficient reporter of pH from pH 5.3 to 6.0 with a fast response of a few seconds. Also the uptake of the t-switch is speedy. In order to protect the t-switch from enzymatic degradation, PEI is used for modification of our DNA nanomachine. At the same time, the dynamic range could be extended to pH 4.6-7.8. The successful application of this pH-depended DNA nanomachine and motoring spatiotemporal pH changes associated with endocytosis is strong evidence of the possibility of self-assembly DNA nanomachine for imaging, targeted therapies, and controllable drug delivery.
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Affiliation(s)
- Mengqi Yang
- Key
Laboratory of Cluster Science of Ministry of Education, Beijing Key
Laboratory of Photoelectronic/Electrophotonic Conversion Materials,
School of Chemistry, Beijing Institute of
Technology, 5 Zhongguancun
Road, Beijing 100081, P. R. China
| | - Xiaoling Zhang
- Key
Laboratory of Cluster Science of Ministry of Education, Beijing Key
Laboratory of Photoelectronic/Electrophotonic Conversion Materials,
School of Chemistry, Beijing Institute of
Technology, 5 Zhongguancun
Road, Beijing 100081, P. R. China
| | - Haipeng Liu
- College
of Engineering, Wayne State University, Detroit, Michigan 48202, United States
| | - Huaizhi Kang
- College
of Chemistry and Chemical Engineering, Xiamen
University, Xiamen, Fujian 361005, P.
R. China
| | - Zhi Zhu
- College
of Chemistry and Chemical Engineering, Xiamen
University, Xiamen, Fujian 361005, P.
R. China
| | - Wen Yang
- Key
Laboratory of Cluster Science of Ministry of Education, Beijing Key
Laboratory of Photoelectronic/Electrophotonic Conversion Materials,
School of Chemistry, Beijing Institute of
Technology, 5 Zhongguancun
Road, Beijing 100081, P. R. China
| | - Weihong Tan
- Center
for Research at Bio/nano Interface, Department
of Chemistry, Department of Physiology and
Functional Genomics, Shands Cancer Center, UF Genetics Institute, and McKnight Brain Institute, University of
Florida, Gainesville, Florida 32611-7200, United States
- Molecular
Science and Biomedicine Laboratory, State Key Laboratory of Chemo/Biosensing
and Chemometrics, College of Chemistry and Chemical Engineering, College
of Biology, Collaborative Innovation Center for Molecular Engineering
and Theranostics, Hunan University, Changsha 410082, P. R. China
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31
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Abstract
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In
this work, we apply the recently developed constant pH molecular
dynamics technique to study protonation equilibria of titratable side
chains in the context of simple transmembrane (TM) helices and explore
the effect of pH on their configurations in membrane bilayers. We
observe that, despite a significant shift toward neutral states, considerable
population of different side chains stay in the charged state that
give rise to pKa values around 9.6 for
Asp and Glu and 4.5 to 6 for His and Lys side chains, respectively.
These charged states are highly stabilized by favorable interactions
between head groups, water molecules, and the charged side chains
that are facilitated by substantial changes in the configuration of
the peptides. The pH dependent configurations and the measured pKa values are in good agreement with relatively
recent solid state NMR measurements. Our results presented here demonstrate
that all-atom constant pH molecular dynamics can be applied to membrane
proteins and peptides to obtain reliable pKa values and pH dependent behavior for these systems.
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Affiliation(s)
- Afra Panahi
- †Department of Chemistry and ‡Biophysics Program, University of Michigan, 930 N. University Ave., Ann Arbor, Michigan, 48109, United States
| | - Charles L Brooks
- †Department of Chemistry and ‡Biophysics Program, University of Michigan, 930 N. University Ave., Ann Arbor, Michigan, 48109, United States
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32
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Laricheva EN, Goh GB, Dickson A, Brooks CL. pH-dependent transient conformational states control optical properties in cyan fluorescent protein. J Am Chem Soc 2015; 137:2892-900. [PMID: 25647152 PMCID: PMC4394632 DOI: 10.1021/ja509233r] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
A recently engineered mutant of cyan fluorescent protein (WasCFP) that exhibits pH-dependent absorption suggests that its tryptophan-based chromophore switches between neutral (protonated) and charged (deprotonated) states depending on external pH. At pH 8.1, the latter gives rise to green fluorescence as opposed to the cyan color of emission that is characteristic for the neutral form at low pH. Given the high energy cost of deprotonating the tryptophan at the indole nitrogen, this behavior is puzzling, even if the stabilizing effect of the V61K mutation in proximity to the protonation/deprotonation site is considered. Because of its potential to open new avenues for the development of optical sensors and photoconvertible fluorescent proteins, a mechanistic understanding of how the charged state in WasCFP can possibly be stabilized is thus important. Attributed to the dynamic nature of proteins, such understanding often requires knowledge of the various conformations adopted, including transiently populated conformational states. Transient conformational states triggered by pH are of emerging interest and have been shown to be important whenever ionizable groups interact with hydrophobic environments. Using a combination of the weighted-ensemble sampling method and explicit-solvent constant pH molecular dynamics (CPHMD(MSλD)) simulations, we have identified a solvated transient state, characterized by a partially open β-barrel where the chromophore pKa of 6.8 is shifted by over 20 units from that of the closed form (6.8 and 31.7, respectively). This state contributes a small population at low pH (12% at pH 6.1) but becomes dominant at mildly basic conditions, contributing as much as 53% at pH 8.1. This pH-dependent population shift between neutral (at pH 6.1) and charged (at pH 8.1) forms is thus responsible for the observed absorption behavior of WasCFP. Our findings demonstrate the conditions necessary to stabilize the charged state of the WasCFP chromophore (namely, local solvation at the deprotonation site and a partial flexibility of the protein β-barrel structure) and provide the first evidence that transient conformational states can control optical properties of fluorescent proteins.
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Affiliation(s)
- Elena N. Laricheva
- Department of Chemistry, University of Michigan, Ann Arbor, Michigan 48109, United States
| | - Garrett B. Goh
- Department of Chemistry, University of Michigan, Ann Arbor, Michigan 48109, United States
| | - Alex Dickson
- Department of Chemistry, University of Michigan, Ann Arbor, Michigan 48109, United States
| | - Charles L. Brooks
- Department of Chemistry, University of Michigan, Ann Arbor, Michigan 48109, United States
- Biophysics Program, University of Michigan, Ann Arbor, Michigan 48109, United States
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33
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Di Russo NV, Martí MA, Roitberg AE. Underlying thermodynamics of pH-dependent allostery. J Phys Chem B 2014; 118:12818-26. [PMID: 25318010 DOI: 10.1021/jp507971v] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Abstract
Understanding the effects of coupling protein protonation and conformational states is critical to the development of drugs targeting pH sensors and to the rational engineering of pH switches. In this work, we address this issue by performing a comprehensive study of the pH-regulated switch from the closed to the open conformation in nitrophorin 4 (NP4) that determines its pH-dependent activity. Our calculations show that D30 is the only amino acid that has two significantly different pKas in the open and closed conformations, confirming its critical role in regulating pH-dependent behavior. In addition, we describe the free-energy landscape of the conformational change as a function of pH, obtaining accurate estimations of free-energy barriers and equilibrium constants using different methods. The underlying thermodynamic model of the switch workings suggests the possibility of tuning the observed pKa only through the conformational equilibria, keeping the same conformation-specific pKas, as evidenced by the proposed K125L mutant. Moreover, coupling between the protonation and conformational equilibria results in efficient regulation and pH-sensing around physiological pH values only for some combinations of protonation and conformational equilibrium constants, placing constraints on their possible values and leaving a narrow space for protein molecular evolution. The calculations and analysis presented here are of general applicability and provide a guide as to how more complex systems can be studied, offering insight into how pH-regulated allostery works of great value for designing drugs that target pH sensors and for rational engineering of pH switches beyond the common histidine trigger.
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Affiliation(s)
- Natali V Di Russo
- Quantum Theory Project and Department of Chemistry, University of Florida , Gainesville, Florida 32611, United States
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34
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Richman DE, Majumdar A, García-Moreno E B. pH dependence of conformational fluctuations of the protein backbone. Proteins 2014; 82:3132-43. [PMID: 25137073 DOI: 10.1002/prot.24673] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/14/2014] [Revised: 06/25/2014] [Accepted: 08/04/2014] [Indexed: 01/08/2023]
Abstract
Proton binding equilibria (pK(a) values) of ionizable groups in proteins are exquisitely sensitive to their microenvironments. Apparent pK(a) values measured for individual ionizable residues with NMR spectroscopy are actually population-weighted averages of the pK(a) in different conformational microstates. NMR spectroscopy experiments with staphylococcal nuclease were used to test the hypothesis that pK(a) values of surface Glu and Asp residues are affected by pH-sensitive fluctuations of the backbone between folded and locally unfolded conformations. (15)N spin relaxation studies showed that as the pH decreases from the neutral into the acidic range the amplitudes of backbone fluctuations in the ps-ns timescale increase near carboxylic residues. Hydrogen exchange experiments suggested that backbone conformational fluctuations promoted by decreasing pH also reflect slower local or sub-global unfolding near carboxylic groups. This study has implications for structure-based pKa calculations: (1) The timescale of the backbone's response to ionization events in proteins can range from ps to ms, and even longer; (2) pH-sensitive fluctuations of the backbone can be localized to both the segment the ionizable residue is attached to or the one that occludes the ionizable group; (3) Structural perturbations are not necessarily propagated through Coulomb interactions; instead, local fluctuations appear to be coupled through the co-operativity inherent to elements of secondary structure and to networks of hydrogen bonds. These results are consistent with the idea that local conformational fluctuations and stabilities are important determinants of apparent pK(a) values of ionizable residues in proteins.
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Affiliation(s)
- Daniel E Richman
- Department of Physics and Astronomy, Johns Hopkins University, Baltimore, Maryland, 21218
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