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Blanco MA. Computational models for studying physical instabilities in high concentration biotherapeutic formulations. MAbs 2022; 14:2044744. [PMID: 35282775 PMCID: PMC8928847 DOI: 10.1080/19420862.2022.2044744] [Citation(s) in RCA: 10] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022] Open
Abstract
Computational prediction of the behavior of concentrated protein solutions is particularly advantageous in early development stages of biotherapeutics when material availability is limited and a large set of formulation conditions needs to be explored. This review provides an overview of the different computational paradigms that have been successfully used in modeling undesirable physical behaviors of protein solutions with a particular emphasis on high-concentration drug formulations. This includes models ranging from all-atom simulations, coarse-grained representations to macro-scale mathematical descriptions used to study physical instability phenomena of protein solutions such as aggregation, elevated viscosity, and phase separation. These models are compared and summarized in the context of the physical processes and their underlying assumptions and limitations. A detailed analysis is also given for identifying protein interaction processes that are explicitly or implicitly considered in the different modeling approaches and particularly their relations to various formulation parameters. Lastly, many of the shortcomings of existing computational models are discussed, providing perspectives and possible directions toward an efficient computational framework for designing effective protein formulations.
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Affiliation(s)
- Marco A. Blanco
- Materials and Biophysical Characterization, Analytical R & D, Merck & Co., Inc, Kenilworth, NJ USA
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Navo CD, Jiménez-Osés G. Computer Prediction of p K a Values in Small Molecules and Proteins. ACS Med Chem Lett 2021; 12:1624-1628. [PMID: 34795846 DOI: 10.1021/acsmedchemlett.1c00435] [Citation(s) in RCA: 9] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022] Open
Abstract
Accurately determining the acid dissociation constants (K a or their logarithmic form, pK a) of small molecules and large biomolecules has proven to be pivotal for the study different biological processes and developing new drugs. This Viewpoint summarizes some of the most common methodologies and recent advances described for pK a prediction using computational techniques when experimental values are not easily accessible such as in proteins and/or for the screening of large libraries of new compounds.
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Affiliation(s)
- Claudio D. Navo
- CIC bioGUNE, Basque Research and Technology Alliance (BRTA), Bizkaia Technology Park, Building 800, Derio 48160, Spain
| | - Gonzalo Jiménez-Osés
- CIC bioGUNE, Basque Research and Technology Alliance (BRTA), Bizkaia Technology Park, Building 800, Derio 48160, Spain
- Ikerbasque, Basque Foundation for Science, 48013 Bilbao, Spain
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Chen J, Hu J, Xu Y, Krasny R, Geng W. Computing Protein pKas Using the TABI Poisson–Boltzmann Solver. JOURNAL OF COMPUTATIONAL BIOPHYSICS AND CHEMISTRY 2021. [DOI: 10.1142/s2737416520420065] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
Abstract
A common approach to computing protein pKas uses a continuum dielectric model in which the protein is a low dielectric medium with embedded atomic point charges, the solvent is a high dielectric medium with a Boltzmann distribution of ionic charges, and the pKa is related to the electrostatic free energy which is obtained by solving the Poisson–Boltzmann equation. Starting from the model pKa for a titrating residue, the method obtains the intrinsic pKa and then computes the protonation probability for a given pH including site–site interactions. This approach assumes that acid dissociation does not affect protein conformation aside from adding or deleting charges at titratable sites. In this work, we demonstrate our treecode-accelerated boundary integral (TABI) solver for the relevant electrostatic calculations. The pKa computing procedure is enclosed in a convenient Python wrapper which is publicly available at the corresponding author’s website. Predicted results are compared with experimental pKas for several proteins. Among ongoing efforts to improve protein pKa calculations, the advantage of TABI is that it reduces the numerical errors in the electrostatic calculations so that attention can be focused on modeling assumptions.
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Affiliation(s)
- Jiahui Chen
- Department of Mathematics, Michigan State University, East Lansing, MI 48824, USA
| | - Jingzhen Hu
- Department of Mathematics, Duke University, Durham, NC 27710, USA
| | - Yongjia Xu
- Department of Mathematics, Southern Methodist University, Dallas, TX 75275, USA
| | - Robert Krasny
- Department of Mathematics, University of Michigan, Ann Arbor, MI 48109, USA
| | - Weihua Geng
- Department of Mathematics, Southern Methodist University, Dallas, TX 75275, USA
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Omelyan I, Kovalenko A. Enhanced solvation force extrapolation for speeding up molecular dynamics simulations of complex biochemical liquids. J Chem Phys 2019; 151:214102. [PMID: 31822083 DOI: 10.1063/1.5126410] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/22/2023] Open
Abstract
We propose an enhanced approach to the extrapolation of mean potential forces acting on atoms of solute macromolecules due to their interactions with solvent atoms in complex biochemical liquids. It improves and extends our previous extrapolation schemes by additionally including new techniques such as an exponential scaling transformation of coordinate space with weights complemented by an automatically adjusted balancing between the least square minimization of force deviations and the norm of expansion coefficients in the approximation. The expensive mean potential forces are treated in terms of the three-dimensional reference interaction site model with Kovalenko-Hirata closure molecular theory of solvation. During the dynamics, they are calculated only after every long (outer) time interval, i.e., quite rarely to reduce the computational costs. At much shorter (inner) time steps, these forces are extrapolated on the basis of their outer values. The equations of motion are then solved using a multiple time step integration within an optimized isokinetic Nosé-Hoover chain thermostat. The new approach is applied to molecular dynamics simulations of various systems consisting of solvated organic and biomolecules of different complexity. For example, we consider hydrated alanine dipeptide, asphaltene in toluene solvent, miniprotein 1L2Y, and protein G in aqueous solution. It is shown that in all these cases, the enhanced extrapolation provides much better accuracy of the solvation force approximation than the existing approaches. As a result, it can be used with much larger outer time steps, leading to a significant speedup of the simulations.
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Affiliation(s)
- Igor Omelyan
- Institute for Condensed Matter Physics, National Academy of Sciences of Ukraine, 1 Svientsitskii Street, Lviv 79011, Ukraine
| | - Andriy Kovalenko
- Department of Mechanical Engineering, University of Alberta, 9211-116 Street NW, Edmonton, Alberta T6G 1H9, Canada
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Cao S, Konovalov KA, Unarta IC, Huang X. Recent Developments in Integral Equation Theory for Solvation to Treat Density Inhomogeneity at Solute–Solvent Interface. ADVANCED THEORY AND SIMULATIONS 2019. [DOI: 10.1002/adts.201900049] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/16/2022]
Affiliation(s)
- Siqin Cao
- Department of Chemistrythe Hong Kong University of Science and Technology Clear Water Bay Kowloon Hong Kong
- Center of System Biology and Human HealthState Key Laboratory of Molecular Neuroscience, Hong Kong Branch Clear Water Bay Kowloon Hong Kong
| | - Kirill A. Konovalov
- Department of Chemistrythe Hong Kong University of Science and Technology Clear Water Bay Kowloon Hong Kong
- Center of System Biology and Human HealthState Key Laboratory of Molecular Neuroscience, Hong Kong Branch Clear Water Bay Kowloon Hong Kong
| | - Ilona Christy Unarta
- Center of System Biology and Human HealthState Key Laboratory of Molecular Neuroscience, Hong Kong Branch Clear Water Bay Kowloon Hong Kong
- Bioengineering Graduate Programthe Hong Kong University of Science and TechnologyHong Kong of Chinese National EngineeringResearch Center for Tissue Restoration and Reconstructionthe Hong Kong University of Science and Technology Clear Water Bay Kowloon Hong Kong
| | - Xuhui Huang
- Department of Chemistrythe Hong Kong University of Science and Technology Clear Water Bay Kowloon Hong Kong
- Center of System Biology and Human HealthState Key Laboratory of Molecular Neuroscience, Hong Kong Branch Clear Water Bay Kowloon Hong Kong
- Bioengineering Graduate Programthe Hong Kong University of Science and TechnologyHong Kong of Chinese National EngineeringResearch Center for Tissue Restoration and Reconstructionthe Hong Kong University of Science and Technology Clear Water Bay Kowloon Hong Kong
- HKUST‐Shenzhen Research Institute Hi‐Tech Park, Nanshan Shenzhen 518057 China
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Pang S, Yang J, Zhao Y, Li Y, Wang J. Computational prediction and functional analysis of arsenic-binding proteins in human cells. QUANTITATIVE BIOLOGY 2019. [DOI: 10.1007/s40484-019-0169-6] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
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Okiyama Y, Nakano T, Watanabe C, Fukuzawa K, Mochizuki Y, Tanaka S. Fragment Molecular Orbital Calculations with Implicit Solvent Based on the Poisson–Boltzmann Equation: Implementation and DNA Study. J Phys Chem B 2018; 122:4457-4471. [DOI: 10.1021/acs.jpcb.8b01172] [Citation(s) in RCA: 30] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/14/2023]
Affiliation(s)
- Yoshio Okiyama
- Institute of Industrial Science, The University of Tokyo, 4-6-1 Komaba, Meguro-ku, Tokyo 153-8505, Japan
| | - Tatsuya Nakano
- Institute of Industrial Science, The University of Tokyo, 4-6-1 Komaba, Meguro-ku, Tokyo 153-8505, Japan
- Division of Medicinal Safety Science, National Institute of Health Sciences, 3-25-26 Tonomachi, Kawasaki-ku, Kawasaki, Kanagawa 210-9501, Japan
| | - Chiduru Watanabe
- Institute of Industrial Science, The University of Tokyo, 4-6-1 Komaba, Meguro-ku, Tokyo 153-8505, Japan
| | - Kaori Fukuzawa
- Institute of Industrial Science, The University of Tokyo, 4-6-1 Komaba, Meguro-ku, Tokyo 153-8505, Japan
- Faculty of Pharmaceutical Sciences, Hoshi University, 2-4-41 Ebara, Shinagawa-ku, Tokyo 142-8501, Japan
| | - Yuji Mochizuki
- Institute of Industrial Science, The University of Tokyo, 4-6-1 Komaba, Meguro-ku, Tokyo 153-8505, Japan
- Department of Chemistry and Research Center for Smart Molecules, Faculty of Science, Rikkyo University, 3-34-1 Nishi-ikebukuro, Toshima-ku, Tokyo 171-8501, Japan
| | - Shigenori Tanaka
- Graduate School of System Informatics, Kobe University, 1-1 Rokkodai, Nada-ku, Kobe, Hyogo 657-8501, Japan
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Machado MR, González HC, Pantano S. MD Simulations of Viruslike Particles with Supra CG Solvation Affordable to Desktop Computers. J Chem Theory Comput 2017; 13:5106-5116. [DOI: 10.1021/acs.jctc.7b00659] [Citation(s) in RCA: 22] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- Matı́as R. Machado
- Biomolecular Simulations
Group, Institut Pasteur de Montevideo, Mataojo 2020, Montevideo CP 11400, Uruguay
| | - Humberto C. González
- Biomolecular Simulations
Group, Institut Pasteur de Montevideo, Mataojo 2020, Montevideo CP 11400, Uruguay
| | - Sergio Pantano
- Biomolecular Simulations
Group, Institut Pasteur de Montevideo, Mataojo 2020, Montevideo CP 11400, Uruguay
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Nanoelectrical characterization of amyloid-β42 aggregates via Kelvin probe force microscopy. Macromol Res 2017. [DOI: 10.1007/s13233-017-5155-0] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/29/2022]
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Omelyan I, Kovalenko A. MTS-MD of Biomolecules Steered with 3D-RISM-KH Mean Solvation Forces Accelerated with Generalized Solvation Force Extrapolation. J Chem Theory Comput 2016; 11:1875-95. [PMID: 26574393 DOI: 10.1021/ct5010438] [Citation(s) in RCA: 28] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022]
Abstract
We developed a generalized solvation force extrapolation (GSFE) approach to speed up multiple time step molecular dynamics (MTS-MD) of biomolecules steered with mean solvation forces obtained from the 3D-RISM-KH molecular theory of solvation (three-dimensional reference interaction site model with the Kovalenko-Hirata closure). GSFE is based on a set of techniques including the non-Eckart-like transformation of coordinate space separately for each solute atom, extension of the force-coordinate pair basis set followed by selection of the best subset, balancing the normal equations by modified least-squares minimization of deviations, and incremental increase of outer time step in motion integration. Mean solvation forces acting on the biomolecule atoms in conformations at successive inner time steps are extrapolated using a relatively small number of best (closest) solute atomic coordinates and corresponding mean solvation forces obtained at previous outer time steps by converging the 3D-RISM-KH integral equations. The MTS-MD evolution steered with GSFE of 3D-RISM-KH mean solvation forces is efficiently stabilized with our optimized isokinetic Nosé-Hoover chain (OIN) thermostat. We validated the hybrid MTS-MD/OIN/GSFE/3D-RISM-KH integrator on solvated organic and biomolecules of different stiffness and complexity: asphaltene dimer in toluene solvent, hydrated alanine dipeptide, miniprotein 1L2Y, and protein G. The GSFE accuracy and the OIN efficiency allowed us to enlarge outer time steps up to huge values of 1-4 ps while accurately reproducing conformational properties. Quasidynamics steered with 3D-RISM-KH mean solvation forces achieves time scale compression of conformational changes coupled with solvent exchange, resulting in further significant acceleration of protein conformational sampling with respect to real time dynamics. Overall, this provided a 50- to 1000-fold effective speedup of conformational sampling for these systems, compared to conventional MD with explicit solvent. We have been able to fold the miniprotein from a fully denatured, extended state in about 60 ns of quasidynamics steered with 3D-RISM-KH mean solvation forces, compared to the average physical folding time of 4-9 μs observed in experiment.
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Affiliation(s)
- Igor Omelyan
- Department of Mechanical Engineering, University of Alberta , Mechanical Engineering Building 4-9, Edmonton, Alberta T6G 2G8, Canada.,National Institute for Nanotechnology, 11421 Saskatchewan Drive, Edmonton, Alberta T6G 2M9, Canada.,Institute for Condensed Matter Physics, National Academy of Sciences of Ukraine , 1 Svientsitskii Street, Lviv 79011, Ukraine
| | - Andriy Kovalenko
- Department of Mechanical Engineering, University of Alberta , Mechanical Engineering Building 4-9, Edmonton, Alberta T6G 2G8, Canada.,National Institute for Nanotechnology, 11421 Saskatchewan Drive, Edmonton, Alberta T6G 2M9, Canada
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Wang B, Lou Z, Zhang H, Xu B. Effect of the electrostatic surface potential on the oligomerization of full-length human recombinant prion protein at single-molecule level. J Chem Phys 2016; 144:114701. [DOI: 10.1063/1.4943878] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022] Open
Affiliation(s)
- Bin Wang
- Single Molecule Study Laboratory, College of Engineering and Nanoscale Science, and Engineering Center, University of Georgia, Athens, Georgia 30605, USA
| | - Zhichao Lou
- Single Molecule Study Laboratory, College of Engineering and Nanoscale Science, and Engineering Center, University of Georgia, Athens, Georgia 30605, USA
- College of Materials Science and Technology, Nanjing University of Aeronautics and Astronautics, Nanjing 210016, People’s Republic of China
| | - Haiqian Zhang
- College of Materials Science and Technology, Nanjing University of Aeronautics and Astronautics, Nanjing 210016, People’s Republic of China
| | - Bingqian Xu
- Single Molecule Study Laboratory, College of Engineering and Nanoscale Science, and Engineering Center, University of Georgia, Athens, Georgia 30605, USA
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Technical advances in molecular simulation since the 1980s. Arch Biochem Biophys 2015; 582:3-9. [PMID: 25772387 DOI: 10.1016/j.abb.2015.03.005] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/03/2015] [Revised: 03/05/2015] [Accepted: 03/06/2015] [Indexed: 12/14/2022]
Abstract
This review describes how the theory and practice of molecular simulation have evolved since the beginning of the 1980s when the author started his career in this field. The account is of necessity brief and subjective and highlights the changes that the author considers have had significant impact on his research and mode of working.
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Martinho N, Florindo H, Silva L, Brocchini S, Zloh M, Barata T. Molecular Modeling to Study Dendrimers for Biomedical Applications. Molecules 2014; 19:20424-20467. [PMID: 25493631 PMCID: PMC6270869 DOI: 10.3390/molecules191220424] [Citation(s) in RCA: 49] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/02/2014] [Revised: 11/12/2014] [Accepted: 11/17/2014] [Indexed: 02/06/2023] Open
Abstract
Molecular modeling techniques provide a powerful tool to study the properties of molecules and their interactions at the molecular level. The use of computational techniques to predict interaction patterns and molecular properties can inform the design of drug delivery systems and therapeutic agents. Dendrimers are hyperbranched macromolecular structures that comprise repetitive building blocks and have defined architecture and functionality. Their unique structural features can be exploited to design novel carriers for both therapeutic and diagnostic agents. Many studies have been performed to iteratively optimise the properties of dendrimers in solution as well as their interaction with drugs, nucleic acids, proteins and lipid membranes. Key features including dendrimer size and surface have been revealed that can be modified to increase their performance as drug carriers. Computational studies have supported experimental work by providing valuable insights about dendrimer structure and possible molecular interactions at the molecular level. The progress in computational simulation techniques and models provides a basis to improve our ability to better predict and understand the biological activities and interactions of dendrimers. This review will focus on the use of molecular modeling tools for the study and design of dendrimers, with particular emphasis on the efforts that have been made to improve the efficacy of this class of molecules in biomedical applications.
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Affiliation(s)
- Nuno Martinho
- Research Institute for Medicines (iMed.ULisboa), Faculty of Pharmacy, Universidade de Lisboa, Av. Professor Gama Pinto, Lisbon 1649-003, Portugal
| | - Helena Florindo
- Research Institute for Medicines (iMed.ULisboa), Faculty of Pharmacy, Universidade de Lisboa, Av. Professor Gama Pinto, Lisbon 1649-003, Portugal
| | - Liana Silva
- Research Institute for Medicines (iMed.ULisboa), Faculty of Pharmacy, Universidade de Lisboa, Av. Professor Gama Pinto, Lisbon 1649-003, Portugal
| | - Steve Brocchini
- Department of Pharmaceutics, The School of Pharmacy, University of London, 29/39 Brunswick Square, London WC1N 1AX, UK
| | - Mire Zloh
- Department of Pharmacy, University of Hertfordshire, College Lane, Hatfield AL10 9AB, UK.
| | - Teresa Barata
- Department of Pharmaceutics, The School of Pharmacy, University of London, 29/39 Brunswick Square, London WC1N 1AX, UK.
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Geitner NK, Wang B, Andorfer RE, Ladner DA, Ke PC, Ding F. Structure-function relationship of PAMAM dendrimers as robust oil dispersants. ENVIRONMENTAL SCIENCE & TECHNOLOGY 2014; 48:12868-12875. [PMID: 25279688 DOI: 10.1021/es5038194] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/03/2023]
Abstract
PAMAM dendrimers have recently been investigated as efficient and biocompatible oil dispersants utilizing their encapsulation capacity; however, their high cationic charge density has been shown to be cytotoxic. It is therefore imperative to mitigate cationic charge-induced toxicity and understand the effects of such changes. Presented here is a synergistic experimental and computational approach to examine the effects of varying terminal surface charge on the capacity of dendrimers to disperse model liner, polycyclic aromatic, and hybrid hydrocarbons. Uncharged dendrimers collapse by forming intramolecular hydrogen bonds, which reduce the hosting capability. On the other hand, changing the surface charges from positive to negative greatly shifts the pKa of tertiary amines of the PAMAM dendrimer interior. As a result, the negatively charged dendrimers have a significant percentage of tertiary amines protonated, ∼30%. This unexpected change in the interior protonation state causes electrostatic interactions with the anionic terminal groups, leading to contraction and a marked decrease in hydrocarbon hosting capacity. The present work highlights the robust nature of dendrimer oil dispersion and also illuminates potentially unintended or unanticipated effects of varying dendrimer surface chemistry on their encapsulation or hosting efficacy, which is important for their environmental, industrial, and biomedical applications.
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Affiliation(s)
- Nicholas K Geitner
- Department of Physics and Astronomy and ‡Department of Environmental Engineering and Earth Sciences, Clemson University , Clemson, South Carolina 29634, United States
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Umadevi P, Senthilkumar L. Influence of metal ions (Zn2+, Cu2+, Ca2+, Mg2+and Na+) on the water coordinated neutral and zwitterionicl-histidine dimer. RSC Adv 2014. [DOI: 10.1039/c4ra08155b] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023] Open
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Borowski T, Broclawik E. Bioinorganic Reaction Mechanisms – Quantum Chemistry Approach. ACTA ACUST UNITED AC 2014. [DOI: 10.1007/978-3-642-28554-7_22] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/18/2023]
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Paldi T. RETRACTED ARTICLE: Deprotonation of Arginines in S4 is Involved in NaChBac Gating. J Membr Biol 2012; 245:761. [DOI: 10.1007/s00232-012-9430-x] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/26/2012] [Accepted: 04/01/2012] [Indexed: 11/29/2022]
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Ullmann RT, Andrade SLA, Ullmann GM. Thermodynamics of transport through the ammonium transporter Amt-1 investigated with free energy calculations. J Phys Chem B 2012; 116:9690-703. [PMID: 22804733 DOI: 10.1021/jp305440f] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023]
Abstract
Amt-1 from Archaeoglobus fulgidus (AfAmt-1) belongs to the Amt/Rh family of ammonium/ammonia transporting membrane proteins. The transport mode and the precise microscopic permeation mechanism utilized by these proteins are intensely debated. Open questions concern the identity of the transported substrate (ammonia and/or ammonium) and whether the transport is passive or active. To address these questions, we studied the overall thermodynamics of the different transport modes as a function of the environmental conditions. Then, we investigated the thermodynamics of the underlying microscopic transport mechanisms with free energy calculations within a continuum electrostatics model. The formalism developed for this purpose is of general utility in the calculation of binding free energies for ligands with multiple protonation forms or other binding forms. The results of our calculations are compared to the available experimental and theoretical data on Amt/Rh proteins and discussed in light of the current knowledge on the physiological conditions experienced by microorganisms and plants. We found that microscopic models of electroneutral and electrogenic transport modes are in principle thermodynamically viable. However, only the electrogenic variants have a net thermodynamic driving force under the physiological conditions experienced by microorganisms and plants. Thus, the transport mechanism of AfAmt-1 is most likely electrogenic.
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Affiliation(s)
- R Thomas Ullmann
- Structural Biology/Bioinformatics, University of Bayreuth, Universitätsstrasse 30, BGI, 95447 Bayreuth, Germany.
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