51
|
Pieri E, Ledentu V, Huix-Rotllant M, Ferré N. Sampling the protonation states: the pH-dependent UV absorption spectrum of a polypeptide dyad. Phys Chem Chem Phys 2018; 20:23252-23261. [DOI: 10.1039/c8cp03557a] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022]
Abstract
When a chromophore interacts with several titratable molecular sites, the modeling of its photophysical properties requires to take into account all their probable protonation states.
Collapse
|
52
|
Geronimo I, Payne CM, Sandgren M. The role of catalytic residue pKa on the hydrolysis/transglycosylation partition in family 3 β-glucosidases. Org Biomol Chem 2018; 16:316-324. [DOI: 10.1039/c7ob02558k] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022]
Abstract
The catalytic acid/base residue (E441) pKa, as modulated by its electrostatic environment, has potential impact on the hydrolysis/transglycosylation partition in β-glucosidases.
Collapse
Affiliation(s)
- Inacrist Geronimo
- Department of Molecular Sciences
- Swedish University of Agricultural Sciences
- 750 07 Uppsala
- Sweden
| | - Christina M. Payne
- Department of Chemical and Materials Engineering
- University of Kentucky
- Lexington
- USA
| | - Mats Sandgren
- Department of Molecular Sciences
- Swedish University of Agricultural Sciences
- 750 07 Uppsala
- Sweden
| |
Collapse
|
53
|
Guzmán-Ocampo DC, Aguayo-Ortiz R, Cano-González L, Castillo R, Hernández-Campos A, Dominguez L. Effects of the Protonation State of Titratable Residues and the Presence of Water Molecules on Nocodazole Binding to β-Tubulin. ChemMedChem 2017; 13:20-24. [PMID: 29059502 DOI: 10.1002/cmdc.201700530] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/04/2017] [Revised: 10/18/2017] [Indexed: 01/18/2023]
Abstract
Regulation of microtubule assembly by antimitotic agents is a potential therapeutic strategy for the treatment of cancer, parasite infections, and neurodegenerative diseases. One of these agents is nocodazole (NZ), which inhibits microtubule polymerization by binding to β-tubulin. NZ was recently co-crystallized in Gallus gallus tubulin, providing new information about the features of interaction for ligand recognition and stability. In this work, we used state-of-the-art computational approaches to evaluate the protonation effects of titratable residues and the presence of water molecules in the binding of NZ. Analysis of protonation states showed that residue E198 has the largest modification in its pKa value. The resulting E198 pKa value, calculated with pH-REMD methodology (pKa =6.21), was higher than the isolated E amino acid (pKa =4.25), thus being more likely to be found in its protonated state at the binding site. Moreover, we identified an interaction between a water molecule and C239 and G235 as essential for NZ binding. Our results suggest that the protonation state of E198 and the structural water molecules play key roles in the binding of NZ to β-tubulin.
Collapse
Affiliation(s)
- Dulce C Guzmán-Ocampo
- Facultad de Química, Departamento de Fisicoquímica, Universidad Nacional Autónoma de México, Mexico City, 04510, Mexico
| | - Rodrigo Aguayo-Ortiz
- Facultad de Química, Departamento de Fisicoquímica, Universidad Nacional Autónoma de México, Mexico City, 04510, Mexico
| | - Lucia Cano-González
- Facultad de Química, Departamento de Farmacia, Universidad Nacional Autónoma de México, Mexico City, 04510, Mexico
| | - Rafael Castillo
- Facultad de Química, Departamento de Farmacia, Universidad Nacional Autónoma de México, Mexico City, 04510, Mexico
| | - Alicia Hernández-Campos
- Facultad de Química, Departamento de Farmacia, Universidad Nacional Autónoma de México, Mexico City, 04510, Mexico
| | - Laura Dominguez
- Facultad de Química, Departamento de Fisicoquímica, Universidad Nacional Autónoma de México, Mexico City, 04510, Mexico
| |
Collapse
|
54
|
Yue Z, Chen W, Zgurskaya HI, Shen J. Constant pH Molecular Dynamics Reveals How Proton Release Drives the Conformational Transition of a Transmembrane Efflux Pump. J Chem Theory Comput 2017; 13:6405-6414. [PMID: 29117682 DOI: 10.1021/acs.jctc.7b00874] [Citation(s) in RCA: 49] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
AcrB is the inner-membrane transporter of an E. coli AcrAB-TolC tripartite efflux complex, which plays a major role in the intrinsic resistance to clinically important antibiotics. AcrB pumps a wide range of toxic substrates by utilizing the proton gradient between periplasm and cytoplasm. Crystal structures of AcrB revealed three distinct conformational states of the transport cycle, substrate access, binding, and extrusion or loose (L), tight (T), and open (O) states. However, the specific residue(s) responsible for proton binding/release and the mechanism of proton-coupled conformational cycling remain controversial. Here we use the newly developed membrane hybrid-solvent continuous constant pH molecular dynamics technique to explore the protonation states and conformational dynamics of the transmembrane domain of AcrB. Simulations show that both Asp407 and Asp408 are deprotonated in the L/T states, while only Asp408 is protonated in the O state. Remarkably, release of a proton from Asp408 in the O state results in large conformational changes, such as the lateral and vertical movement of transmembrane helices as well as the salt-bridge formation between Asp408 and Lys940 and other side chain rearrangements among essential residues. Consistent with the crystallographic differences between the O and L protomers, simulations offer dynamic details of how proton release drives the O-to-L transition in AcrB and address the controversy regarding the proton/drug stoichiometry. This work offers a significant step toward characterizing the complete cycle of proton-coupled drug transport in AcrB and further validates the membrane hybrid-solvent CpHMD technique for studies of proton-coupled transmembrane proteins which are currently poorly understood.
Collapse
Affiliation(s)
- Zhi Yue
- Department of Pharmaceutical Sciences, University of Maryland School of Pharmacy , Baltimore, Maryland 21201, United States
| | | | - Helen I Zgurskaya
- Department of Chemistry and Biochemistry, University of Oklahoma , Norman, Oklahoma 73019, United States
| | - Jana Shen
- Department of Pharmaceutical Sciences, University of Maryland School of Pharmacy , Baltimore, Maryland 21201, United States
| |
Collapse
|
55
|
Yeager AV, Swails JM, Miller BR. Improved Accuracy for Constant pH-REMD Simulations through Modification of Carboxylate Effective Radii. J Chem Theory Comput 2017; 13:4624-4635. [DOI: 10.1021/acs.jctc.7b00638] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Affiliation(s)
- Andrew V. Yeager
- Department
of Chemistry, Truman State University, 100 E. Normal Ave., Kirksville, Missouri 63501, United States
| | - Jason M. Swails
- Department
of Chemistry and Chemical Biology and BioMaPS Institute, Rutgers University, Piscataway, New Jersey 08854, United States
| | - Bill R. Miller
- Department
of Chemistry, Truman State University, 100 E. Normal Ave., Kirksville, Missouri 63501, United States
| |
Collapse
|
56
|
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
| | | |
Collapse
|
57
|
Izmailov SA, Podkorytov IS, Skrynnikov NR. Simple MD-based model for oxidative folding of peptides and proteins. Sci Rep 2017; 7:9293. [PMID: 28839177 PMCID: PMC5570944 DOI: 10.1038/s41598-017-09229-7] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/13/2016] [Accepted: 07/17/2017] [Indexed: 11/14/2022] Open
Abstract
Significant strides have been recently made to fold peptides and small proteins in silico using MD simulations. However, facilities are currently lacking to include disulfide bonding in the MD models of protein folding. To address this problem, we have developed a simple empirical protocol to model formation of disulfides, which is perturbation-free, retains the same speed as conventional MD simulations and allows one to control the reaction rate. The new protocol has been tested on 15-aminoacid peptide guanylin containing four cysteine residues; the net simulation time using Amber ff14SB force field was 61 μs. The resulting isomer distribution is in qualitative agreement with experiment, suggesting that oxidative folding of guanylin in vitro occurs under kinetic control. The highly stable conformation of the so-called isomer 2(B) has been obtained for full-length guanylin, which is significantly different from the poorly ordered structure of the truncated peptide PDB ID 1GNB. In addition, we have simulated oxidative folding of guanylin within the 94-aminoacid prohormone proguanylin. The obtained structure is in good agreement with the NMR coordinates 1O8R. The proposed modeling strategy can help to explore certain fundamental aspects of protein folding and is potentially relevant for manufacturing of synthetic peptides and recombinant proteins.
Collapse
Affiliation(s)
- Sergei A Izmailov
- Laboratory of Biomolecular NMR, St. Petersburg State University, St. Petersburg, 199034, Russia
| | - Ivan S Podkorytov
- Laboratory of Biomolecular NMR, St. Petersburg State University, St. Petersburg, 199034, Russia
| | - Nikolai R Skrynnikov
- Laboratory of Biomolecular NMR, St. Petersburg State University, St. Petersburg, 199034, Russia.
- Department of Chemistry, Purdue University, West Lafayette, IN, 47907, USA.
| |
Collapse
|
58
|
Prati F, Bottegoni G, Bolognesi ML, Cavalli A. BACE-1 Inhibitors: From Recent Single-Target Molecules to Multitarget Compounds for Alzheimer’s Disease. J Med Chem 2017; 61:619-637. [DOI: 10.1021/acs.jmedchem.7b00393] [Citation(s) in RCA: 70] [Impact Index Per Article: 10.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
Affiliation(s)
- Federica Prati
- Drug Discovery Unit,
Division of Biological Chemistry and Drug Discovery, College of Life
Sciences, University of Dundee, Dow Street, Dundee, DD1 5EH, Scotland, U.K
| | - Giovanni Bottegoni
- CompuNet, Istituto Italiano di Tecnologia, Via Morego 30, 16163 Genova, Italy
- Heptares Therapeutics Ltd., BioPark, Broadwater Road, Welwyn Garden City, Hertfordshire AL7 3AX, U.K
| | - Maria Laura Bolognesi
- Department
of Pharmacy and Biotechnology, Alma Mater Studiorum-University of Bologna, Via Belmeloro 6, 40126 Bologna, Italy
| | - Andrea Cavalli
- CompuNet, Istituto Italiano di Tecnologia, Via Morego 30, 16163 Genova, Italy
- Department
of Pharmacy and Biotechnology, Alma Mater Studiorum-University of Bologna, Via Belmeloro 6, 40126 Bologna, Italy
| |
Collapse
|
59
|
Ganesan A, Coote ML, Barakat K. Molecular dynamics-driven drug discovery: leaping forward with confidence. Drug Discov Today 2017; 22:249-269. [DOI: 10.1016/j.drudis.2016.11.001] [Citation(s) in RCA: 133] [Impact Index Per Article: 19.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/21/2016] [Revised: 09/22/2016] [Accepted: 11/01/2016] [Indexed: 12/11/2022]
|
60
|
Trozzi F, Marforio TD, Bottoni A, Zerbetto F, Calvaresi M. Engineering the Fullerene-protein Interface by Computational Design: The Sum is More than its Parts. Isr J Chem 2016. [DOI: 10.1002/ijch.201600127] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022]
Affiliation(s)
- Francesco Trozzi
- Dipartimento di Chimica “G. Ciamician”; Alma Mater Studiorum; Università di Bologna; via F. Selmi 2 40126 Bologna Italy
| | - Tainah Dorina Marforio
- Dipartimento di Chimica “G. Ciamician”; Alma Mater Studiorum; Università di Bologna; via F. Selmi 2 40126 Bologna Italy
| | - Andrea Bottoni
- Dipartimento di Chimica “G. Ciamician”; Alma Mater Studiorum; Università di Bologna; via F. Selmi 2 40126 Bologna Italy
| | - Francesco Zerbetto
- Dipartimento di Chimica “G. Ciamician”; Alma Mater Studiorum; Università di Bologna; via F. Selmi 2 40126 Bologna Italy
| | - Matteo Calvaresi
- Dipartimento di Chimica “G. Ciamician”; Alma Mater Studiorum; Università di Bologna; via F. Selmi 2 40126 Bologna Italy
| |
Collapse
|
61
|
Mechanism of pH-dependent activation of the sodium-proton antiporter NhaA. Nat Commun 2016; 7:12940. [PMID: 27708266 PMCID: PMC5059715 DOI: 10.1038/ncomms12940] [Citation(s) in RCA: 73] [Impact Index Per Article: 9.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/03/2016] [Accepted: 08/17/2016] [Indexed: 11/08/2022] Open
Abstract
Escherichia coli NhaA is a prototype sodium-proton antiporter, which has been extensively characterized by X-ray crystallography, biochemical and biophysical experiments. However, the identities of proton carriers and details of pH-regulated mechanism remain controversial. Here we report constant pH molecular dynamics data, which reveal that NhaA activation involves a net charge switch of a pH sensor at the entrance of the cytoplasmic funnel and opening of a hydrophobic gate at the end of the funnel. The latter is triggered by charging of Asp164, the first proton carrier. The second proton carrier Lys300 forms a salt bridge with Asp163 in the inactive state, and releases a proton when a sodium ion binds Asp163. These data reconcile current models and illustrate the power of state-of-the-art molecular dynamics simulations in providing atomic details of proton-coupled transport across membrane which is challenging to elucidate by experimental techniques. The pH dependence of the activity of Escherichia coli main sodium-proton antiporter NhaA is still not fully understood. Here, the authors use continuous constant pH molecular dynamics simulations to identify NhaA proton carrier residues and elucidate its gating and ion transport processes.
Collapse
|
62
|
Purvine E, Monson K, Jurrus E, Star K, Baker NA. Energy Minimization of Discrete Protein Titration State Models Using Graph Theory. J Phys Chem B 2016; 120:8354-60. [PMID: 27089174 DOI: 10.1021/acs.jpcb.6b02059] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
There are several applications in computational biophysics that require the optimization of discrete interacting states, for example, amino acid titration states, ligand oxidation states, or discrete rotamer angles. Such optimization can be very time-consuming as it scales exponentially in the number of sites to be optimized. In this paper, we describe a new polynomial time algorithm for optimization of discrete states in macromolecular systems. This algorithm was adapted from image processing and uses techniques from discrete mathematics and graph theory to restate the optimization problem in terms of "maximum flow-minimum cut" graph analysis. The interaction energy graph, a graph in which vertices (amino acids) and edges (interactions) are weighted with their respective energies, is transformed into a flow network in which the value of the minimum cut in the network equals the minimum free energy of the protein and the cut itself encodes the state that achieves the minimum free energy. Because of its deterministic nature and polynomial time performance, this algorithm has the potential to allow for the ionization state of larger proteins to be discovered.
Collapse
Affiliation(s)
| | | | | | | | - Nathan A Baker
- Division of Applied Mathematics, Brown University , Providence, Rhode Island 02912, United States
| |
Collapse
|
63
|
Ellis CR, Tsai CC, Hou X, Shen J. Constant pH Molecular Dynamics Reveals pH-Modulated Binding of Two Small-Molecule BACE1 Inhibitors. J Phys Chem Lett 2016; 7:944-9. [PMID: 26905811 PMCID: PMC5713896 DOI: 10.1021/acs.jpclett.6b00137] [Citation(s) in RCA: 38] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 05/16/2023]
Abstract
Targeting β-secretase (BACE1) with small-molecule inhibitors offers a promising route for treatment of Alzheimer's disease. However, the intricate pH dependence of BACE1 function and inhibitor efficacy has posed major challenges for structure-based drug design. Here we investigate two structurally similar BACE1 inhibitors that have dramatically different inhibitory activity using continuous constant pH molecular dynamics (CpHMD). At high pH, both inhibitors are stably bound to BACE1; however, within the enzyme active pH range, only the iminopyrimidinone-based inhibitor remains bound, while the aminothiazine-based inhibitor becomes partially dissociated following the loss of hydrogen bonding with the active site and change of the 10s loop conformation. The drastically lower activity of the second inhibitor is due to the protonation of a catalytic aspartate and the lack of a propyne tail. This work demonstrates that CpHMD can be used for screening pH-dependent binding profiles of small-molecule inhibitors, providing a new tool for structure-based drug design and optimization.
Collapse
Affiliation(s)
- Christopher R. Ellis
- Department of Pharmaceutical Sciences, University of Maryland School of Pharmacy, Baltimore, MD
| | - Cheng-Chieh Tsai
- Department of Pharmaceutical Sciences, University of Maryland School of Pharmacy, Baltimore, MD
| | - Xinjun Hou
- Neuroscience Worldwide Medicinal Chemistry, Pfizer Worldwide Research and Development, Cambridge, MA
| | - Jana Shen
- Department of Pharmaceutical Sciences, University of Maryland School of Pharmacy, Baltimore, MD
- Corresponding Author:
| |
Collapse
|
64
|
Capelli R, Villemot F, Moroni E, Tiana G, van der Vaart A, Colombo G. Assessment of Mutational Effects on Peptide Stability through Confinement Simulations. J Phys Chem Lett 2016; 7:126-130. [PMID: 26678679 DOI: 10.1021/acs.jpclett.5b02221] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/05/2023]
Abstract
The evaluation of free energy differences between specific states of a system is of fundamental interest in the study of (bio)chemical systems. Herein, we examine the use of the recently introduced confinement method (CM) to evaluate relative free energy changes upon protein/peptide mutations. CM is a path-independent technique that involves the transformation of a configurational state of the system into an ideal crystal permitting the direct computation of free energy differences. We illustrate the method by evaluating the differential stabilities between native and mutant sequences of a model peptide that has been extensively characterized by experimental approaches, the GB1 hairpin. We show a good correlation between calculated and experimental relative stabilities and discuss other possible applications of this method in the context of complex molecular conversions.
Collapse
Affiliation(s)
- Riccardo Capelli
- Dipartimento di Fisica, Università degli Studi di Milano and INFN , via Celoria 16, 20133 Milan, Italy
- Istituto di Chimica del Riconoscimento Molecolare, Consiglio Nazionale delle Ricerche , via Mario Bianco 9, 20131 Milan, Italy
| | - François Villemot
- Department of Chemistry, University of South Florida , 4202 East Fowler Avenue, CHE 205, Tampa, Florida 33620, United States
| | - Elisabetta Moroni
- Istituto di Chimica del Riconoscimento Molecolare, Consiglio Nazionale delle Ricerche , via Mario Bianco 9, 20131 Milan, Italy
| | - Guido Tiana
- Dipartimento di Fisica, Università degli Studi di Milano and INFN , via Celoria 16, 20133 Milan, Italy
- Center for Complexity and Biosystems and Department of Physics, Università degli Studi di Milano and INFN , via Celoria 16, 20133 Milan, Italy
| | - Arjan van der Vaart
- Department of Chemistry, University of South Florida , 4202 East Fowler Avenue, CHE 205, Tampa, Florida 33620, United States
| | - Giorgio Colombo
- Istituto di Chimica del Riconoscimento Molecolare, Consiglio Nazionale delle Ricerche , via Mario Bianco 9, 20131 Milan, Italy
| |
Collapse
|
65
|
Kim MO, McCammon JA. Computation of pH-dependent binding free energies. Biopolymers 2016; 105:43-9. [PMID: 26202905 PMCID: PMC4623928 DOI: 10.1002/bip.22702] [Citation(s) in RCA: 19] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/28/2015] [Accepted: 07/20/2015] [Indexed: 01/21/2023]
Abstract
Protein-ligand binding accompanies changes in the surrounding electrostatic environments of the two binding partners and may lead to changes in protonation upon binding. In cases where the complex formation results in a net transfer of protons, the binding process is pH-dependent. However, conventional free energy computations or molecular docking protocols typically employ fixed protonation states for the titratable groups in both binding partners set a priori, which are identical for the free and bound states. In this review, we draw attention to these important yet largely ignored binding-induced protonation changes in protein-ligand association by outlining physical origins and prevalence of the protonation changes upon binding. Following a summary of various theoretical methods for pKa prediction, we discuss the theoretical framework to examine the pH dependence of protein-ligand binding processes.
Collapse
Affiliation(s)
- M. Olivia Kim
- Department of Pharmacology, University of California San Diego, La Jolla, CA 92093, USA
| | - J. Andrew McCammon
- Department of Pharmacology, University of California San Diego, La Jolla, CA 92093, USA
- Department of Chemistry and Biochemistry, University of California San Diego, La Jolla, CA 92093, USA
- Howard Hughes Medical Institute, University of California San Diego, La Jolla, CA 92093, USA
- National Biomedical Computation Resource, University of California San Diego, La Jolla, CA 92093, USA
| |
Collapse
|
66
|
Bodnarchuk MS, Heyes DM, Dini D, Chahine S, Edwards S. Role of Deprotonation Free Energies in pKa Prediction and Molecule Ranking. J Chem Theory Comput 2015; 10:2537-45. [PMID: 26580774 DOI: 10.1021/ct400914w] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
A computationally efficient classical molecular simulation technique is derived for ranking the pKa values of a set of chemically similar congeneric molecules in an implicit solvent model of water. This uses the deprotonation free energy of the titratable group in the gas and aqueous phases obtained by thermodynamic integration (TI). For a series of alcohols and acids a strong linear correlation is demonstrated between the experimental pKa and the deprotonation free energy difference in the gas and liquid phases. These calculations also show that classical TI is more efficient than slow-growth TI in calculating deprotonation free energies for the series of molecules considered herein.
Collapse
Affiliation(s)
- M S Bodnarchuk
- Department of Mechanical Engineering, Imperial College London , Exhibition Road, London, SW7 2AZ, U.K
| | - D M Heyes
- Department of Mechanical Engineering, Imperial College London , Exhibition Road, London, SW7 2AZ, U.K
| | - D Dini
- Department of Mechanical Engineering, Imperial College London , Exhibition Road, London, SW7 2AZ, U.K
| | - S Chahine
- BP Marine Limited, Marine Technology Centre , Whitchurch Hill, Pangbourne, RG8 7QR, U.K
| | - S Edwards
- BP Marine Limited, Marine Technology Centre , Whitchurch Hill, Pangbourne, RG8 7QR, U.K
| |
Collapse
|
67
|
Conformational Dynamics and Binding Free Energies of Inhibitors of BACE-1: From the Perspective of Protonation Equilibria. PLoS Comput Biol 2015; 11:e1004341. [PMID: 26506513 PMCID: PMC4623973 DOI: 10.1371/journal.pcbi.1004341] [Citation(s) in RCA: 29] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/24/2015] [Accepted: 05/17/2015] [Indexed: 11/19/2022] Open
Abstract
BACE-1 is the β-secretase responsible for the initial amyloidogenesis in Alzheimer’s disease, catalyzing hydrolytic cleavage of substrate in a pH-sensitive manner. The catalytic mechanism of BACE-1 requires water-mediated proton transfer from aspartyl dyad to the substrate, as well as structural flexibility in the flap region. Thus, the coupling of protonation and conformational equilibria is essential to a full in silico characterization of BACE-1. In this work, we perform constant pH replica exchange molecular dynamics simulations on both apo BACE-1 and five BACE-1-inhibitor complexes to examine the effect of pH on dynamics and inhibitor binding properties of BACE-1. In our simulations, we find that solution pH controls the conformational flexibility of apo BACE-1, whereas bound inhibitors largely limit the motions of the holo enzyme at all levels of pH. The microscopic pKa values of titratable residues in BACE-1 including its aspartyl dyad are computed and compared between apo and inhibitor-bound states. Changes in protonation between the apo and holo forms suggest a thermodynamic linkage between binding of inhibitors and protons localized at the dyad. Utilizing our recently developed computational protocol applying the binding polynomial formalism to the constant pH molecular dynamics (CpHMD) framework, we are able to obtain the pH-dependent binding free energy profiles for various BACE-1-inhibitor complexes. Our results highlight the importance of correctly addressing the binding-induced protonation changes in protein-ligand systems where binding accompanies a net proton transfer. This work comprises the first application of our CpHMD-based free energy computational method to protein-ligand complexes and illustrates the value of CpHMD as an all-purpose tool for obtaining pH-dependent dynamics and binding free energies of biological systems. Formation of insoluble amyloid plaques in the vascular and hippocampal areas of the brain characterizes Alzheimer’s disease, a devastating neurodegenerative disorder causing dementia. Site-specific hydrolytic catalysis of β-secretase, or BACE-1, is responsible for production of oligomerative amyloid β-peptide. As the catalytic activity of BACE-1 is pH-dependent and its structural dynamics are intrinsic to the catalysis, we examine the dependence of dynamics of BACE-1 on solution pH and its implications on the catalytic mechanism of BACE-1. Also, we highlight the importance of accurate description of protonation states of the titratable groups in computer-aided drug discovery targeting BACE-1. We hope the understanding of pH dependence of the dynamics and inhibitor binding properties of BACE-1 will aid the structure-based inhibitor design efforts against Alzheimer’s disease.
Collapse
|
68
|
Vila-Viçosa D, Teixeira VH, Baptista AM, Machuqueiro M. Constant-pH MD Simulations of an Oleic Acid Bilayer. J Chem Theory Comput 2015; 11:2367-76. [DOI: 10.1021/acs.jctc.5b00095] [Citation(s) in RCA: 27] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Affiliation(s)
- Diogo Vila-Viçosa
- Centro
de Química e Bioquímica and Departamento de Química
e Bioquímica, Faculdade de Ciências, Universidade de Lisboa, Edifı́cio C8 Campo Grande, 1749-016 Lisboa, Portugal
| | - Vitor H. Teixeira
- Centro
de Química e Bioquímica and Departamento de Química
e Bioquímica, Faculdade de Ciências, Universidade de Lisboa, Edifı́cio C8 Campo Grande, 1749-016 Lisboa, Portugal
| | - António M. Baptista
- Instituto
de Tecnologia Química e Biológica, Universidade Nova de Lisboa, Av. da República, 2780-157 Oeiras, Portugal
| | - Miguel Machuqueiro
- Centro
de Química e Bioquímica and Departamento de Química
e Bioquímica, Faculdade de Ciências, Universidade de Lisboa, Edifı́cio C8 Campo Grande, 1749-016 Lisboa, Portugal
| |
Collapse
|
69
|
Bracht F, de Alencastro RB. Dynamical study, hydrogen bond analysis, and constant pH simulations of the beta carbonic anhydrase ofMethanobacterium thermoautotrophicum. J Biomol Struct Dyn 2015; 34:259-71. [DOI: 10.1080/07391102.2015.1025100] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/23/2022]
|
70
|
Zarzycki P, Smith DM, Rosso KM. Proton Dynamics on Goethite Nanoparticles and Coupling to Electron Transport. J Chem Theory Comput 2015; 11:1715-24. [DOI: 10.1021/ct500891a] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023]
Affiliation(s)
- Piotr Zarzycki
- Institute
of Physical Chemistry, Polish Academy of Sciences, 01-224 Warsaw, Poland
| | - Dayle M. Smith
- Pacific Northwest National Laboratory, Richland, Washington 99354, United States
| | - Kevin M. Rosso
- Pacific Northwest National Laboratory, Richland, Washington 99354, United States
| |
Collapse
|
71
|
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.
Collapse
Affiliation(s)
- Natali V Di Russo
- Quantum Theory Project and Department of Chemistry, University of Florida , Gainesville, Florida 32611, United States
| | | | | |
Collapse
|
72
|
McGee TD, Edwards J, Roitberg AE. pH-REMD Simulations Indicate That the Catalytic Aspartates of HIV-1 Protease Exist Primarily in a Monoprotonated State. J Phys Chem B 2014; 118:12577-85. [DOI: 10.1021/jp504011c] [Citation(s) in RCA: 35] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- T. Dwight McGee
- Department
of Chemistry, Quantum Theory Project, University of Florida, Gainesville, Florida 32611, United States
| | - Jesse Edwards
- Department
of Chemistry, Florida Agricultural and Mechanical University, Tallahassee, Florida 32307, United States
| | - Adrian E. Roitberg
- Department
of Chemistry, Quantum Theory Project, University of Florida, Gainesville, Florida 32611, United States
| |
Collapse
|
73
|
Ugur I, Marion A, Parant S, Jensen JH, Monard G. Rationalization of the pKa Values of Alcohols and Thiols Using Atomic Charge Descriptors and Its Application to the Prediction of Amino Acid pKa’s. J Chem Inf Model 2014; 54:2200-13. [DOI: 10.1021/ci500079w] [Citation(s) in RCA: 52] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- Ilke Ugur
- Université de Lorraine, UMR 7565 SRSMC, Boulevard des Aiguillettes B.P. 70239, F-54506 Vandoeuvre-les-Nancy, France
- CNRS, UMR 7565 SRSMC, Boulevard
des Aiguillettes B.P. 70239, F-54506 Vandoeuvre-les-Nancy, France
- Department
of Chemistry, Boğaziçi University, 34342 Bebek, Istanbul, Turkey
| | - Antoine Marion
- Université de Lorraine, UMR 7565 SRSMC, Boulevard des Aiguillettes B.P. 70239, F-54506 Vandoeuvre-les-Nancy, France
- CNRS, UMR 7565 SRSMC, Boulevard
des Aiguillettes B.P. 70239, F-54506 Vandoeuvre-les-Nancy, France
| | - Stéphane Parant
- Université de Lorraine, UMR 7565 SRSMC, Boulevard des Aiguillettes B.P. 70239, F-54506 Vandoeuvre-les-Nancy, France
- CNRS, UMR 7565 SRSMC, Boulevard
des Aiguillettes B.P. 70239, F-54506 Vandoeuvre-les-Nancy, France
| | - Jan H. Jensen
- Department
of Chemistry, University of Copenhagen, Copenhagen, Denmark
| | - Gerald Monard
- Université de Lorraine, UMR 7565 SRSMC, Boulevard des Aiguillettes B.P. 70239, F-54506 Vandoeuvre-les-Nancy, France
- CNRS, UMR 7565 SRSMC, Boulevard
des Aiguillettes B.P. 70239, F-54506 Vandoeuvre-les-Nancy, France
| |
Collapse
|
74
|
Chen W, Morrow BH, Shi C, Shen JK. Recent development and application of constant pH molecular dynamics. MOLECULAR SIMULATION 2014; 40:830-838. [PMID: 25309035 DOI: 10.1080/08927022.2014.907492] [Citation(s) in RCA: 82] [Impact Index Per Article: 8.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/08/2023]
Abstract
Solution pH is a critical environmental factor for chemical and biological processes. Over the last decade, significant efforts have been made in the development of constant pH molecular dynamics (pHMD) techniques for gaining detailed insights into pH-coupled dynamical phenomena. In this article we review the advancement of this field in the past five years, placing a special emphasis on the development of the all-atom continuous pHMD technique. We discuss various applications, including the prediction of pKa shifts for proteins, nucleic acids and surfactant assemblies, elucidation of pH-dependent population shifts, protein-protein and protein-RNA binding, as well as the mechanisms of pH-dependent self-assembly and phase transitions of surfactants and peptides. We also discuss future directions for the further improvement of the pHMD techniques.
Collapse
Affiliation(s)
- Wei Chen
- Department of Pharmaceutical Sciences, School of Pharmacy, University of Maryland, Baltimore, MD 21201, USA
| | - Brian H Morrow
- Department of Pharmaceutical Sciences, School of Pharmacy, University of Maryland, Baltimore, MD 21201, USA
| | - Chuanyin Shi
- Eastern Hepatobiliary Surgery Hospital, Second Military Medical University, Shanghai 200438, China
| | - Jana K Shen
- Department of Pharmaceutical Sciences, School of Pharmacy, University of Maryland, Baltimore, MD 21201, USA
| |
Collapse
|
75
|
Temelso B, Alser KA, Gauthier A, Palmer AK, Shields GC. Structural Analysis of α-Fetoprotein (AFP)-like Peptides with Anti-Breast-Cancer Properties. J Phys Chem B 2014; 118:4514-26. [DOI: 10.1021/jp500017b] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023]
Affiliation(s)
- Berhane Temelso
- Dean’s
Office, College of Arts and Sciences, and Department of Chemistry, Bucknell University, Lewisburg, Pennsylvania 17837, United States
- Dean’s Office, College of Science and Technology, and Department of Chemistry & Physics, Armstrong Atlantic State University, 11935 Abercorn Street, Savannah, Georgia 31419, United States
| | - Katherine A. Alser
- Dean’s
Office, College of Arts and Sciences, and Department of Chemistry, Bucknell University, Lewisburg, Pennsylvania 17837, United States
| | - Arianne Gauthier
- Dean’s Office, College of Science and Technology, and Department of Chemistry & Physics, Armstrong Atlantic State University, 11935 Abercorn Street, Savannah, Georgia 31419, United States
| | - Amber Kay Palmer
- Dean’s Office, College of Science and Technology, and Department of Chemistry & Physics, Armstrong Atlantic State University, 11935 Abercorn Street, Savannah, Georgia 31419, United States
| | - George C. Shields
- Dean’s
Office, College of Arts and Sciences, and Department of Chemistry, Bucknell University, Lewisburg, Pennsylvania 17837, United States
- Dean’s Office, College of Science and Technology, and Department of Chemistry & Physics, Armstrong Atlantic State University, 11935 Abercorn Street, Savannah, Georgia 31419, United States
| |
Collapse
|
76
|
Granum DM, Schutt TC, Maupin CM. Computational Evaluation of the Dynamic Fluctuations of Peripheral Loops Enclosing the Catalytic Tunnel of a Family 7 Cellobiohydrolase. J Phys Chem B 2014; 118:5340-9. [DOI: 10.1021/jp5011555] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- David M. Granum
- Chemical
and Biological Engineering
Department, Colorado School of Mines, 1500 Illinois Street, Golden, Colorado 80401, United States
| | - Timothy C. Schutt
- Chemical
and Biological Engineering
Department, Colorado School of Mines, 1500 Illinois Street, Golden, Colorado 80401, United States
| | - C. Mark Maupin
- Chemical
and Biological Engineering
Department, Colorado School of Mines, 1500 Illinois Street, Golden, Colorado 80401, United States
| |
Collapse
|
77
|
Swails JM, York DM, Roitberg AE. Constant pH Replica Exchange Molecular Dynamics in Explicit Solvent Using Discrete Protonation States: Implementation, Testing, and Validation. J Chem Theory Comput 2014; 10:1341-1352. [PMID: 24803862 PMCID: PMC3985686 DOI: 10.1021/ct401042b] [Citation(s) in RCA: 176] [Impact Index Per Article: 17.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/02/2013] [Indexed: 12/24/2022]
Abstract
![]()
By
utilizing Graphics Processing Units, we show that constant pH
molecular dynamics simulations (CpHMD) run in Generalized Born (GB)
implicit solvent for long time scales can yield poor pKa predictions as a result of sampling unrealistic conformations.
To address this shortcoming, we present a method for performing constant
pH molecular dynamics simulations (CpHMD) in explicit solvent using
a
discrete protonation state model. The method involves standard molecular
dynamics (MD) being propagated in explicit solvent followed by protonation
state changes being attempted in GB implicit solvent at fixed intervals.
Replica exchange along the pH-dimension (pH-REMD) helps to obtain
acceptable titration behavior with the proposed method. We analyzed
the effects of various parameters and settings on the titration behavior
of CpHMD and pH-REMD in explicit solvent, including the size of the
simulation unit cell and the length of the relaxation dynamics following
protonation state changes. We tested the method with the amino acid
model compounds, a small pentapeptide with two titratable sites, and
hen egg white lysozyme (HEWL). The proposed method yields superior
predicted pKa values for HEWL over hundreds
of nanoseconds of simulation relative to corresponding predicted values
from simulations run in implicit solvent.
Collapse
Affiliation(s)
- Jason M Swails
- Quantum Theory Project, Chemistry Department, University of Florida , Gainesville, Florida 32611, United States
| | - Darrin M York
- BioMaPS Institute for Quantitative Biology, Center for Integrative Proteomics Research, and Department of Chemistry and Chemical Biology, Rutgers University , Piscataway, New Jersey 08901, United States
| | - Adrian E Roitberg
- Quantum Theory Project, Chemistry Department, University of Florida , Gainesville, Florida 32611, United States
| |
Collapse
|
78
|
Goh GB, Hulbert BS, Zhou H, Brooks CL. Constant pH molecular dynamics of proteins in explicit solvent with proton tautomerism. Proteins 2014; 82:1319-31. [PMID: 24375620 DOI: 10.1002/prot.24499] [Citation(s) in RCA: 86] [Impact Index Per Article: 8.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/11/2013] [Revised: 11/13/2013] [Accepted: 12/12/2013] [Indexed: 12/14/2022]
Abstract
pH is a ubiquitous regulator of biological activity, including protein-folding, protein-protein interactions, and enzymatic activity. Existing constant pH molecular dynamics (CPHMD) models that were developed to address questions related to the pH-dependent properties of proteins are largely based on implicit solvent models. However, implicit solvent models are known to underestimate the desolvation energy of buried charged residues, increasing the error associated with predictions that involve internal ionizable residue that are important in processes like hydrogen transport and electron transfer. Furthermore, discrete water and ions cannot be modeled in implicit solvent, which are important in systems like membrane proteins and ion channels. We report on an explicit solvent constant pH molecular dynamics framework based on multi-site λ-dynamics (CPHMD(MSλD)). In the CPHMD(MSλD) framework, we performed seamless alchemical transitions between protonation and tautomeric states using multi-site λ-dynamics, and designed novel biasing potentials to ensure that the physical end-states are predominantly sampled. We show that explicit solvent CPHMD(MSλD) simulations model realistic pH-dependent properties of proteins such as the Hen-Egg White Lysozyme (HEWL), binding domain of 2-oxoglutarate dehydrogenase (BBL) and N-terminal domain of ribosomal protein L9 (NTL9), and the pKa predictions are in excellent agreement with experimental values, with a RMSE ranging from 0.72 to 0.84 pKa units. With the recent development of the explicit solvent CPHMD(MSλD) framework for nucleic acids, accurate modeling of pH-dependent properties of both major class of biomolecules-proteins and nucleic acids is now possible.
Collapse
Affiliation(s)
- Garrett B Goh
- Department of Chemistry, University of Michigan, Ann Arbor, Michigan, 48109
| | | | | | | |
Collapse
|
79
|
Granum DM, Vyas S, Sambasivarao SV, Maupin CM. Computational Evaluations of Charge Coupling and Hydrogen Bonding in the Active Site of a Family 7 Cellobiohydrolase. J Phys Chem B 2014; 118:434-48. [DOI: 10.1021/jp408536s] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- David M. Granum
- Chemical and Biological Engineering Department and ‡Chemistry and Geochemistry Department, Colorado School of Mines, 1500 Illinois Street, Golden, Colorado 80401, United States
| | - Shubham Vyas
- Chemical and Biological Engineering Department and ‡Chemistry and Geochemistry Department, Colorado School of Mines, 1500 Illinois Street, Golden, Colorado 80401, United States
| | - Somisetti V. Sambasivarao
- Chemical and Biological Engineering Department and ‡Chemistry and Geochemistry Department, Colorado School of Mines, 1500 Illinois Street, Golden, Colorado 80401, United States
| | - C. Mark Maupin
- Chemical and Biological Engineering Department and ‡Chemistry and Geochemistry Department, Colorado School of Mines, 1500 Illinois Street, Golden, Colorado 80401, United States
| |
Collapse
|
80
|
Burger SK, Schofield J, Ayers PW. Quantum mechanics/molecular mechanics restrained electrostatic potential fitting. J Phys Chem B 2013; 117:14960-6. [PMID: 24176005 DOI: 10.1021/jp409568h] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
We present a quantum mechanics/molecular mechanics (QM/MM) method to evaluate the partial charges of amino acid residues for use in MM potentials based on their protein environment. For each residue of interest, the nearby residues are included in the QM system while the rest of the protein is treated at the MM level of theory. After a short structural optimization, the partial charges of the central residue are fit to the electrostatic potential using the restrained electrostatic potential (RESP) method. The resulting charges and electrostatic potential account for the individual environment of the residue, although they lack the transferable nature of library partial charges. To evaluate the quality of the QM/MM RESP charges, thermodynamic integration is used to measure the pKa shift of the aspartic acid residues in three different proteins, turkey egg lysozyme, beta-cryptogein, and Thioredoxin. Compared to the AMBER ff99SB library values, the QM/MM RESP charges show better agreement between the calculated and experimental pK(a) values for almost all of the residues considered.
Collapse
Affiliation(s)
- Steven K Burger
- Department of Chemistry, University of Toronto , 80 St. George Street, Toronto, Ontario M5S 3H6, Canada
| | | | | |
Collapse
|
81
|
|
82
|
Bu L, Crowley MF, Himmel ME, Beckham GT. Computational investigation of the pH dependence of loop flexibility and catalytic function in glycoside hydrolases. J Biol Chem 2013; 288:12175-86. [PMID: 23504310 DOI: 10.1074/jbc.m113.462465] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Cellulase enzymes cleave glycosidic bonds in cellulose to produce cellobiose via either retaining or inverting hydrolysis mechanisms, which are significantly pH-dependent. Many fungal cellulases function optimally at pH ~5, and their activities decrease dramatically at higher or lower pH. To understand the molecular-level implications of pH in cellulase structure, we use a hybrid, solvent-based, constant pH molecular dynamics method combined with pH-based replica exchange to determine the pK(a) values of titratable residues of a glycoside hydrolase (GH) family 6 cellobiohydrolase (Cel6A) and a GH family 7 cellobiohydrolase (Cel7A) from the fungus Hypocrea jecorina. For both enzymes, we demonstrate that a bound substrate significantly affects the pKa values of the acid residues at the catalytic center. The calculated pK(a) values of catalytic residues confirm their proposed roles from structural studies and are consistent with the experimentally measured apparent pKa values. Additionally, GHs are known to impart a strained pucker conformation in carbohydrate substrates in active sites for catalysis, and results from free energy calculations combined with constant pH molecular dynamics suggest that the correct ring pucker is stable near the optimal pH for both Cel6A and Cel7A. Much longer molecular dynamics simulations of Cel6A and Cel7A with fixed protonation states based on the calculated pK(a) values suggest that pH affects the flexibility of tunnel loops, which likely affects processivity and substrate complexation. Taken together, this work demonstrates several molecular-level effects of pH on GH enzymes important for cellulose turnover in the biosphere and relevant to biomass conversion processes.
Collapse
Affiliation(s)
- Lintao Bu
- National Bioenergy Center, Colorado School of Mines, Golden, Colorado 80401, USA.
| | | | | | | |
Collapse
|
83
|
Goh GB, Knight JL, Brooks CL. Towards Accurate Prediction of Protonation Equilibrium of Nucleic Acids. J Phys Chem Lett 2013; 4:760-766. [PMID: 23526474 PMCID: PMC3601767 DOI: 10.1021/jz400078d] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/02/2023]
Abstract
The role of protonated nucleotides in modulating the pH-dependent properties of nucleic acids is one of the emerging frontiers in the field of nucleic acid biology. The recent development of a constant pH molecular dynamics simulation (CPHMDMSλD) framework for simulating nucleic acids has provided a tool for realistic simulations of pH-dependent dynamics. We enhanced the CPHMDMSλD framework with pH-based replica exchange (pH-REX), which significantly improves the sampling of both titration and spatial coordinates. The results from our pKa calculations for the GAAA tetraloop, which was predicted with lower accuracy previously due to sampling challenges, demonstrates that pH-REX reduces the average unsigned error (AUE) to 0.7 pKa units, and the error of the most poorly predicted residue A17 was drastically reduced from 2.9 to 1.2 pKa unit. Lastly, we show that pH-REX CPHMDMSλD simulations can be used to identify the dominant conformation of nucleic acid structures in alternate pH environments. This work suggests that pH-REX CPHMDMSλD simulations provide a practical tool for predicting nucleic acid protonation equilibrium from first-principles, and offering structural and mechanistic insight into the study of pH-dependent properties of nucleic acids.
Collapse
Affiliation(s)
- Garrett B Goh
- Department of Chemistry, University of Michigan, 930 N. University, Ann Arbor, Michigan 48109, United States
| | | | | |
Collapse
|