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Penhallurick RW, Ichiye T. Pressure Adaptations in Deep-Sea Moritella Dihydrofolate Reductases: Compressibility versus Stability. BIOLOGY 2021; 10:biology10111211. [PMID: 34827204 PMCID: PMC8614765 DOI: 10.3390/biology10111211] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 10/21/2021] [Revised: 11/17/2021] [Accepted: 11/17/2021] [Indexed: 11/25/2022]
Abstract
Simple Summary Deep-sea organisms must have proteins that function under high hydrostatic pressure to survive. Adaptations used in proteins from “pressure-loving” piezophiles may include greater compressibility or greater stability against pressure-induced destabilization. However, while greater compressibility can be accomplished by greater void volume, larger cavities in a protein have been associated with greater destabilization and even unfolding as pressure is increased. Here, computer simulations of dihydrofolate reductase from a moderate piezophile and a hyperpiezophile were performed to understand the balance between adaptations for greater compressibility and those against pressure destabilization and unfolding. The results indicate that while compressibility appears to be important for deep-sea microbes, adaptation for the greatest depths may be to prevent water penetration into the interior. Abstract Proteins from “pressure-loving” piezophiles appear to adapt by greater compressibility via larger total cavity volume. However, larger cavities in proteins have been associated with lower unfolding pressures. Here, dihydrofolate reductase (DHFR) from a moderate piezophile Moritella profunda (Mp) isolated at ~2.9 km in depth and from a hyperpiezophile Moritella yayanosii (My) isolated at ~11 km in depth were compared using molecular dynamics simulations. Although previous simulations indicate that MpDHFR is more compressible than a mesophile DHFR, here the average properties and a quasiharmonic analysis indicate that MpDHFR and MyDHFR have similar compressibilities. A cavity analysis also indicates that the three unique mutations in MyDHFR are near cavities, although the cavities are generally similar in size in both. However, while a cleft overlaps an internal cavity, thus forming a pathway from the surface to the interior in MpDHFR, the unique residue Tyr103 found in MyDHFR forms a hydrogen bond with Leu78, and the sidechain separates the cleft from the cavity. Thus, while Moritella DHFR may generally be well suited to high-pressure environments because of their greater compressibility, adaptation for greater depths may be to prevent water entry into the interior cavities.
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Response of neutrophilic Shewanella violacea to acid stress: growth rate, organic acid production, and gene expression. Extremophiles 2019; 23:319-326. [DOI: 10.1007/s00792-019-01083-x] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/05/2018] [Accepted: 02/15/2019] [Indexed: 12/20/2022]
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Li XG, Zhang WJ, Xiao X, Jian HH, Jiang T, Tang HZ, Qi XQ, Wu LF. Pressure-Regulated Gene Expression and Enzymatic Activity of the Two Periplasmic Nitrate Reductases in the Deep-Sea Bacterium Shewanella piezotolerans WP3. Front Microbiol 2018; 9:3173. [PMID: 30622525 PMCID: PMC6308320 DOI: 10.3389/fmicb.2018.03173] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/12/2018] [Accepted: 12/07/2018] [Indexed: 01/06/2023] Open
Abstract
Shewanella species are widely distributed in marine environments, from the shallow coasts to the deepest sea bottom. Most Shewanella species possess two isoforms of periplasmic nitrate reductases (NAP-α and NAP-β) and are able to generate energy through nitrate reduction. However, the contributions of the two NAP systems to bacterial deep-sea adaptation remain unclear. In this study, we found that the deep-sea denitrifier Shewanella piezotolerans WP3 was capable of performing nitrate respiration under high hydrostatic pressure (HHP) conditions. In the wild-type strain, NAP-β played a dominant role and was induced by both the substrate and an elevated pressure, whereas NAP-α was constitutively expressed at a relatively lower level. Genetic studies showed that each NAP system alone was sufficient to fully sustain nitrate-dependent growth and that both NAP systems exhibited substrate and pressure inducible expression patterns when the other set was absent. Biochemical assays further demonstrated that NAP-α had a higher tolerance to elevated pressure. Collectively, we report for the first time the distinct properties and contributions of the two NAP systems to nitrate reduction under different pressure conditions. The results will shed light on the mechanisms of bacterial HHP adaptation and nitrogen cycling in the deep-sea environment.
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Affiliation(s)
- Xue-Gong Li
- Laboratory of Deep Sea Microbial Cell Biology, Institute of Deep-Sea Science and Engineering, Chinese Academy of Sciences, Sanya, China.,International Associated Laboratory of Evolution and Development of Magnetotactic Multicellular Organisms, CNRS-Marseille/CAS, Sanya, China
| | - Wei-Jia Zhang
- Laboratory of Deep Sea Microbial Cell Biology, Institute of Deep-Sea Science and Engineering, Chinese Academy of Sciences, Sanya, China.,International Associated Laboratory of Evolution and Development of Magnetotactic Multicellular Organisms, CNRS-Marseille/CAS, Sanya, China
| | - Xiang Xiao
- State Key Laboratory of Microbial Metabolism, School of Life Sciences and Biotechnology, Shanghai Jiao Tong University, Shanghai, China.,State Key Laboratory of Ocean Engineering, School of Naval Architecture, Ocean and Civil Engineering, Shanghai Jiao Tong University, Shanghai, China
| | - Hua-Hua Jian
- State Key Laboratory of Microbial Metabolism, School of Life Sciences and Biotechnology, Shanghai Jiao Tong University, Shanghai, China
| | - Ting Jiang
- Laboratory of Deep Sea Microbial Cell Biology, Institute of Deep-Sea Science and Engineering, Chinese Academy of Sciences, Sanya, China.,University of Chinese Academy of Sciences, Beijing, China
| | - Hong-Zhi Tang
- Laboratory of Deep Sea Microbial Cell Biology, Institute of Deep-Sea Science and Engineering, Chinese Academy of Sciences, Sanya, China.,University of Chinese Academy of Sciences, Beijing, China
| | - Xiao-Qing Qi
- Laboratory of Deep Sea Microbial Cell Biology, Institute of Deep-Sea Science and Engineering, Chinese Academy of Sciences, Sanya, China.,International Associated Laboratory of Evolution and Development of Magnetotactic Multicellular Organisms, CNRS-Marseille/CAS, Sanya, China
| | - Long-Fei Wu
- International Associated Laboratory of Evolution and Development of Magnetotactic Multicellular Organisms, CNRS-Marseille/CAS, Sanya, China.,Aix Marseille Université, CNRS, LCB, Marseille, France
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Pressure adaptation of 3-isopropylmalate dehydrogenase from an extremely piezophilic bacterium is attributed to a single amino acid substitution. Extremophiles 2016; 20:177-86. [PMID: 26847201 DOI: 10.1007/s00792-016-0811-4] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/19/2015] [Accepted: 01/15/2016] [Indexed: 10/22/2022]
Abstract
3-Isopropylmalate dehydrogenase (IPMDH) from the extreme piezophile Shewanella benthica (SbIPMDH) is more pressure-tolerant than that from the atmospheric pressure-adapted Shewanella oneidensis (SoIPMDH). To understand the molecular mechanisms of this pressure tolerance, we analyzed mutated enzymes. The results indicate that only a single mutation at position 266, corresponding to Ala (SbIPMDH) and Ser (SoIPMDH), essentially affects activity under higher-pressure conditions. Structural analyses of SoIPMDH suggests that penetration of three water molecules into the cleft around Ser266 under high-pressure conditions could reduce the activity of the wild-type enzyme; however, no water molecule is observed in the Ala266 mutant.
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Hamajima Y, Nagae T, Watanabe N, Kato-Yamada Y, Imai T, Kato C. Pressure effects on the chimeric 3-isopropylmalate dehydrogenases of the deep-sea piezophilic Shewanella benthica and the atmospheric pressure-adapted Shewanella oneidensis. Biosci Biotechnol Biochem 2014; 78:469-71. [DOI: 10.1080/09168451.2014.890033] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/25/2022]
Abstract
Abstract
The chimeric 3-isopropylmalate dehydrogenase enzymes were constructed from the deep-sea piezophilic Shewanella benthica and the shallow water Shewanella oneidensis genes. The properties of the enzymatic activities under pressure conditions indicated that the central region, which contained the active center and the dimer forming domains, was shown to be the most important region for pressure tolerance in the deep-sea enzyme.
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Affiliation(s)
- Yuki Hamajima
- Department of Life Science, Rikkyo University, Tokyo, Japan
- Institute of Biogeosciences, Japan Agency for Marine-Earth Science and Technology, Yokosuka, Japan
| | - Takayuki Nagae
- Department of Biotechnology, Graduate School of Engineering, Nagoya University, Nagoya, Japan
| | - Nobuhisa Watanabe
- Department of Biotechnology, Graduate School of Engineering, Nagoya University, Nagoya, Japan
- Synchrotron Radiation Research Center, Nagoya University, Nagoya, Japan
| | | | - Takeo Imai
- Department of Life Science, Rikkyo University, Tokyo, Japan
| | - Chiaki Kato
- Institute of Biogeosciences, Japan Agency for Marine-Earth Science and Technology, Yokosuka, Japan
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Regulation of cytochrome c- and quinol oxidases, and piezotolerance of their activities in the deep-sea piezophile Shewanella violacea DSS12 in response to growth conditions. Biosci Biotechnol Biochem 2013; 77:1522-8. [PMID: 23832349 DOI: 10.1271/bbb.130197] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
The facultative piezophile Shewanella violacea DSS12 is known to have respiratory components that alter under the influence of hydrostatic pressure during growth, suggesting that its respiratory system is adapted to high pressure. We analyzed the expression of the genes encoding terminal oxidases and some respiratory components of DSS12 under various growth conditions. The expression of some of the genes during growth was regulated by both the O2 concentration and hydrostatic pressure. Additionally, the activities of cytochrome c oxidase and quinol oxidase of the membrane fraction of DSS12 grown under various conditions were measured under high pressure. The piezotolerance of cytochrome c oxidase activity was dependent on the O2 concentration during growth, while that of quinol oxidase was influenced by pressure during growth. The activity of quinol oxidase was more piezotolerant than that of cytochrome c oxidase under all growth conditions. Even in the membranes of the non-piezophile Shewanella amazonensis, quinol oxidase was more piezotolerant than cytochrome c oxidase, although both were highly piezosensitive as compared to the activities in DSS12. By phylogenetic analysis, piezophile-specific cytochrome c oxidase, which is also found in the genome of DSS12, was identified in piezophilic Shewanella and related genera. Our observations suggest that DSS12 constitutively expresses piezotolerant respiratory terminal oxidases, and that lower O2 concentrations and higher hydrostatic pressures induce higher piezotolerance in both types of terminal oxidases. Quinol oxidase might be the dominant terminal oxidase in high-pressure environments, while cytochrome c oxidase might also contribute. These features should contribute to adaptation of DSS12 in deep-sea environments.
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Nagae T, Kato C, Watanabe N. Structural analysis of 3-isopropylmalate dehydrogenase from the obligate piezophile Shewanella benthica DB21MT-2 and the nonpiezophile Shewanella oneidensis MR-1. Acta Crystallogr Sect F Struct Biol Cryst Commun 2012; 68:265-8. [PMID: 22442218 PMCID: PMC3310526 DOI: 10.1107/s1744309112001443] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/28/2011] [Accepted: 01/12/2012] [Indexed: 11/10/2022]
Abstract
Organisms living in deep seas such as the Mariana Trench must be adapted to the extremely high pressure environment. For example, the 3-isopropylmalate dehydrogenase from the obligate piezophile Shewanella benthica DB21MT-2 (SbIPMDH) remains active in extreme conditions under which that from the land bacterium S. oneidensis MR-1 (SoIPMDH) becomes inactivated. In order to unravel the differences between these two IPMDHs, their structures were determined at ~1.5 Å resolution. Comparison of the structures of the two enzymes shows that SbIPMDH is in a more open form and has a larger internal cavity volume than SoIPMDH at atmospheric pressure. This loosely packed structure of SbIPMDH could help it to avoid pressure-induced distortion of the native structure and to remain active at higher pressures than SoIPMDH.
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Affiliation(s)
- Takayuki Nagae
- Department of Biotechnology, Graduate School of Engineering, Nagoya University, Japan
| | - Chiaki Kato
- Institute of Biogeosciences, Japan Agency for Marine-Earth Science and Technology (JAMSTEC), Japan
| | - Nobuhisa Watanabe
- Department of Biotechnology, Graduate School of Engineering, Nagoya University, Japan
- Synchrotron Radiation Research Center, Nagoya University, Japan
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Pressure dependence of activity and stability of dihydrofolate reductases of the deep-sea bacterium Moritella profunda and Escherichia coli. BIOCHIMICA ET BIOPHYSICA ACTA-PROTEINS AND PROTEOMICS 2012; 1824:511-9. [PMID: 22266402 DOI: 10.1016/j.bbapap.2012.01.001] [Citation(s) in RCA: 35] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/04/2011] [Revised: 12/19/2011] [Accepted: 01/02/2012] [Indexed: 11/20/2022]
Abstract
To understand the pressure-adaptation mechanism of deep-sea enzymes, we studied the effects of pressure on the enzyme activity and structural stability of dihydrofolate reductase (DHFR) of the deep-sea bacterium Moritella profunda (mpDHFR) in comparison with those of Escherichia coli (ecDHFR). mpDHFR exhibited optimal enzyme activity at 50MPa whereas ecDHFR was monotonically inactivated by pressure, suggesting inherent pressure-adaptation mechanisms in mpDHFR. The secondary structure of apo-mpDHFR was stable up to 80°C, as revealed by circular dichroism spectra. The free energy changes due to pressure and urea unfolding of apo-mpDHFR, determined by fluorescence spectroscopy, were smaller than those of ecDHFR, indicating the unstable structure of mpDHFR against pressure and urea despite the three-dimensional crystal structures of both DHFRs being almost the same. The respective volume changes due to pressure and urea unfolding were -45 and -53ml/mol at 25°C for mpDHFR, which were smaller (less negative) than the corresponding values of -77 and -85ml/mol for ecDHFR. These volume changes can be ascribed to the difference in internal cavity and surface hydration of each DHFR. From these results, we assume that the native structure of mpDHFR is loosely packed and highly hydrated compared with that of ecDHFR in solution.
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Piezotolerance of the respiratory terminal oxidase activity of the piezophilic Shewanella violacea DSS12 as compared with non-piezophilic Shewanella species. Biosci Biotechnol Biochem 2011; 75:919-24. [PMID: 21597190 DOI: 10.1271/bbb.100882] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
The facultative piezophile Shewanella violacea DSS12 is known to alter its respiratory components under the influence of hydrostatic pressure during growth, suggesting that it has a respiratory system that functions in adaptation to high pressure. We investigated the pressure- and temperature-dependencies of the respiratory terminal oxidase activity of the membrane of S. violacea relative to non-piezophilic Shewanella species. We observed that the activity in the membrane of S. violacea was more resistant to high pressure than those of non-piezophilic Shewanella even though DSS12 was cultured under atmospheric pressure. On the other hand, the temperature dependency of this activity was almost the same for all of the tested strain regardless of optimal growth temperature. Both high pressure and low temperature are expected to lower protein flexibility, causing a decrease in enzyme activity, but the results of this study suggest that the mechanism maintaining enzyme activity under high hydrostatic pressure is different from that at low temperature. Additionally, the responses of the activity to the pressure- and temperature-changes were independent of membrane lipid composition. Therefore, the piezotolerance of the respiratory terminal oxidases of S. violacea is perhaps dependent on the properties of the protein itself and not on the lipid composition of the membrane. Our observations suggest that S. violacea constitutively express piezotolerant respiratory terminal oxidases that serve adaptation to the deep-sea environment.
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Murakami C, Ohmae E, Tate SI, Gekko K, Nakasone K, Kato C. Comparative study on dihydrofolate reductases from Shewanella species living in deep-sea and ambient atmospheric-pressure environments. Extremophiles 2010; 15:165-75. [PMID: 21181485 DOI: 10.1007/s00792-010-0345-0] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/21/2010] [Accepted: 12/01/2010] [Indexed: 10/18/2022]
Abstract
To examine whether dihydrofolate reductase (DHFR) from deep-sea bacteria has undergone molecular evolution to adapt to high-pressure environments, we cloned eight DHFRs from Shewanella species living in deep-sea and ambient atmospheric-pressure environments, and subsequently purified six proteins to compare their structures, stabilities, and functions. The DHFRs showed 74-90% identity in primary structure to DHFR from S. violacea, but only 55% identity to DHFR from Escherichia coli (ecDHFR). Far-ultraviolet circular dichroism and fluorescence spectra suggested that the secondary and tertiary structures of these DHFRs were similar. In addition, no significant differences were found in structural stability as monitored by urea-induced unfolding and the kinetic parameters, K(m) and k(cat); although the DHFRs from Shewanella species were less stable and more active (2- to 4-fold increases in k(cat)/K(m)) than ecDHFR. Interestingly, the pressure effects on enzyme activity revealed that DHFRs from ambient-atmospheric species are not necessarily incompatible with high pressure, and DHFRs from deep-sea species are not necessarily tolerant of high pressure. These results suggest that the DHFR molecule itself has not evolved to adapt to high-pressure environments, but rather, those Shewanella species with enzymes capable of retaining functional activity under high pressure migrated into the deep-sea.
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Affiliation(s)
- Chiho Murakami
- Department of Mathematical and Life Sciences, Graduate School of Science, Hiroshima University, Higashi-Hiroshima 739-8526, Japan
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Abstract
The manipulation of biological materials using elevated pressure is providing an ever-growing number of opportunities in both the applied and basic sciences. Manipulation of pressure is a useful parameter for enhancing food quality and shelf life; inactivating microbes, viruses, prions, and deleterious enzymes; affecting recombinant protein production; controlling DNA hybridization; and improving vaccine preparation. In biophysics and biochemistry, pressure is used as a tool to study intermediates in protein folding, enzyme kinetics, macromolecular interactions, amyloid fibrous protein aggregation, lipid structural changes, and to discern the role of solvation and void volumes in these processes. Biologists, including many microbiologists, examine the utility and basis of pressure inactivation of cells and cellular processes, and conversely seek to discover how deep-sea life has evolved a preference for high-pressure environments. This introduction and the papers that follow provide information on the nature and promise of the highly interdisciplinary field of high-pressure bioscience and biotechnology (HPBB).
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Affiliation(s)
- Douglas H Bartlett
- Center for Marine Biotechnology and Biomedicine, Scripps Institution of Oceanography, University of California, San Diego, USA.
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Murakami C, Ohmae E, Tate SI, Gekko K, Nakasone K, Kato C. Cloning and characterization of dihydrofolate reductases from deep-sea bacteria. J Biochem 2009; 147:591-9. [DOI: 10.1093/jb/mvp206] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
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Hay S, Evans RM, Levy C, Loveridge EJ, Wang X, Leys D, Allemann RK, Scrutton NS. Are the Catalytic Properties of Enzymes from Piezophilic Organisms Pressure Adapted? Chembiochem 2009; 10:2348-53. [DOI: 10.1002/cbic.200900367] [Citation(s) in RCA: 45] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
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Abstract
This review covers the 390 novel marine natural products described to date from deep-water (>50 m) marine fauna, with details on the source organism, its depth and country of origin, along with any reported biological activity of the metabolites. Relevant synthetic studies on the deep-sea natural products have also been included.
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Affiliation(s)
- Danielle Skropeta
- School of Chemistry, University of Wollongong, Wollongong, Australia.
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Ohmae E, Tatsuta M, Abe F, Kato C, Tanaka N, Kunugi S, Gekko K. Effects of pressure on enzyme function of Escherichia coli dihydrofolate reductase. BIOCHIMICA ET BIOPHYSICA ACTA-PROTEINS AND PROTEOMICS 2008; 1784:1115-21. [PMID: 18472025 DOI: 10.1016/j.bbapap.2008.04.005] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/25/2008] [Revised: 04/07/2008] [Accepted: 04/08/2008] [Indexed: 11/26/2022]
Abstract
To elucidate the effects of pressure on the function of Escherichia coli dihydrofolate reductase (DHFR), the enzyme activity and the dissociation constants of substrates and cofactors were measured at pressures up to 250 MPa at 25 degrees C and pH 7.0. The enzyme activity decreased with increasing pressure, accompanying the activation volume of 7.8 ml mol(-1). The values of the Michaelis constant (K(m)) for dihydrofolate and NADPH were slightly higher at 200 MPa than at atmospheric pressure. The hydride-transfer step was insensitive to pressure, as monitored by the effects of the deuterium isotope of NADPH on the reaction velocity. The dissociation constants of substrates and cofactors increased with pressure, producing volume reductions from 6.5 ml mol(-1) (tetrahydrofolate) to 33.5 ml mol(-1) (NADPH). However, the changes in Gibbs free energy with dissociation of many ligands showed different pressure dependences below and above 50 MPa, suggesting conformational changes of the enzyme at high pressure. The enzyme function at high pressure is discussed based on the volume levels of the intermediates and the candidates for the rate-limiting process.
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Affiliation(s)
- Eiji Ohmae
- Department of Mathematical and Life Sciences, Graduate School of Science, Hiroshima University, Higashi-Hiroshima 739-8526, Japan
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Moghaddam MS, Chan HS. Pressure and temperature dependence of hydrophobic hydration: Volumetric, compressibility, and thermodynamic signatures. J Chem Phys 2007; 126:114507. [PMID: 17381220 DOI: 10.1063/1.2539179] [Citation(s) in RCA: 46] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023] Open
Abstract
The combined effect of pressure and temperature on hydrophobic hydration of a nonpolar methanelike solute is investigated by extensive simulations in the TIP4P model of water. Using test-particle insertion techniques, free energies of hydration under a range of pressures from 1 to 3000 atm are computed at eight temperatures ranging from 278.15 to 368.15 K. Corresponding enthalpy, entropy, and heat capacity accompanying the hydration process are estimated from the temperature dependence of the free energies. Partial molar and excess volumes calculated using pressure derivatives of the simulated free energies are consistent with those determined by direct volume simulations; but direct volume determination offers more reliable estimates for compressibility. At 298.15 K, partial molar and excess isothermal compressibilities of methane are negative at 1 atm. Partial molar and excess adiabatic (isentropic) compressibilities are estimated to be also negative under the same conditions. But partial molar and excess isothermal compressibilities are positive at high pressures, with a crossover from negative to positive compressibility at approximately 100-1000 atm. This trend is consistent with experiments on aliphatic amino acids and pressure-unfolded states of proteins. For the range of pressures simulated, hydration heat capacity exhibits little pressure dependence, also in apparent agreement with experiment. When pressure is raised at constant room temperature, hydration free energy increases while its entropic component remains essentially constant. Thus, the increasing unfavorability of hydration under raised pressure is seen as largely an enthalpic effect. Ramifications of the findings of the authors for biopolymer conformational transitions are discussed.
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Affiliation(s)
- Maria Sabaye Moghaddam
- Department of Biochemistry, Faculty of Medicine, University of Toronto, Toronto, Ontario M5S 1A8, Canada
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