1
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Potassium Glutamate and Glycine Betaine Induce Self-Assembly of the PCNA and β-Sliding Clamps. Biophys J 2020; 120:73-85. [PMID: 33221249 DOI: 10.1016/j.bpj.2020.11.013] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/26/2020] [Revised: 11/06/2020] [Accepted: 11/10/2020] [Indexed: 12/11/2022] Open
Abstract
Sliding clamps are oligomeric ring-shaped proteins that increase the efficiency of DNA replication. The stability of the Escherichia coli β-clamp, a homodimer, is particularly remarkable. The dissociation equilibrium constant of the β-clamp is of the order of 10 pM in buffers of moderate ionic strength. Coulombic electrostatic interactions have been shown to contribute to this remarkable stability. Increasing NaCl concentration in the assay buffer results in decreased dimer stability and faster subunit dissociation kinetics in a way consistent with simple charge-screening models. Here, we examine non-Coulombic ionic effects on the oligomerization properties of sliding clamps. We determined relative diffusion coefficients of two sliding clamps using fluorescence correlation spectroscopy. Replacing NaCl by KGlu, the primary cytoplasmic salt in E. coli, results in a decrease of the diffusion coefficient of these proteins consistent with the formation of protein assemblies. The UV-vis spectrum of the β-clamp labeled with tetramethylrhodamine shows the characteristic absorption band of dimers of rhodamine when KGlu is present in the buffer. This suggests that KGlu induces the formation of assemblies that involve two or more rings stacked face-to-face. Results can be quantitatively explained on the basis of unfavorable interactions between KGlu and the functional groups on the protein surface, which drive biomolecular processes that bury exposed surface. Similar results were obtained with the Saccharomyces cerevisiae PCNA sliding clamp, suggesting that KGlu effects are not specific to the β-clamp. Clamp association is also promoted by glycine betaine, a zwitterionic compound that accumulates intracellularly when E. coli is exposed to high concentrations of extracellular solute. Possible biological implications are discussed.
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2
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Evans ED, Gates ZP, Sun ZYJ, Mijalis AJ, Pentelute BL. Conformational Stabilization and Rapid Labeling of a 29-Residue Peptide by a Small Molecule Reaction Partner. Biochemistry 2019; 58:1343-1353. [DOI: 10.1021/acs.biochem.8b00940] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- Ethan D. Evans
- Department of Chemistry, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, United States
| | - Zachary P. Gates
- Department of Chemistry, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, United States
| | - Zhen-Yu J. Sun
- Department of Biological Chemistry and Molecular Pharmacology, Harvard Medical School, 240 Longwood Avenue, Boston, Massachusetts 02115, United States
| | - Alexander J. Mijalis
- Department of Chemistry, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, United States
| | - Bradley L. Pentelute
- Department of Chemistry, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, United States
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3
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Di Natale C, Celetti G, Scognamiglio PL, Cosenza C, Battista E, Causa F, Netti PA. Molecularly endowed hydrogel with an in silico-assisted screened peptide for highly sensitive small molecule harvesting. Chem Commun (Camb) 2018; 54:10088-10091. [DOI: 10.1039/c8cc04943b] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Schematic representation of in silico-assisted screening of an AFM1 binding peptide and the working principle of toxin harvesting by molecularly endowed hydrogel.
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Affiliation(s)
- Concetta Di Natale
- Center for Advanced Biomaterials for Healthcare
- Istituto Italiano di Tecnologia (IIT)
- Naples 80125
- Italy
| | - Giorgia Celetti
- Center for Advanced Biomaterials for Healthcare
- Istituto Italiano di Tecnologia (IIT)
- Naples 80125
- Italy
| | | | - Chiara Cosenza
- Interdisciplinary Research Centre on Biomaterials (CRIB)
- University “Federico II”
- Naples 80125
- Italy
| | - Edmondo Battista
- Interdisciplinary Research Centre on Biomaterials (CRIB)
- University “Federico II”
- Naples 80125
- Italy
| | - Filippo Causa
- Center for Advanced Biomaterials for Healthcare
- Istituto Italiano di Tecnologia (IIT)
- Naples 80125
- Italy
- Interdisciplinary Research Centre on Biomaterials (CRIB)
| | - Paolo A. Netti
- Center for Advanced Biomaterials for Healthcare
- Istituto Italiano di Tecnologia (IIT)
- Naples 80125
- Italy
- Interdisciplinary Research Centre on Biomaterials (CRIB)
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4
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Heyda J, Okur HI, Hladílková J, Rembert KB, Hunn W, Yang T, Dzubiella J, Jungwirth P, Cremer PS. Guanidinium can both Cause and Prevent the Hydrophobic Collapse of Biomacromolecules. J Am Chem Soc 2017; 139:863-870. [PMID: 28054487 PMCID: PMC5499822 DOI: 10.1021/jacs.6b11082] [Citation(s) in RCA: 63] [Impact Index Per Article: 9.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022]
Abstract
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A combination of Fourier transform
infrared and phase transition
measurements as well as molecular computer simulations, and thermodynamic
modeling were performed to probe the mechanisms by which guanidinium
(Gnd+) salts influence the stability of the collapsed versus
uncollapsed state of an elastin-like polypeptide (ELP), an uncharged
thermoresponsive polymer. We found that the cation’s action
was highly dependent upon the counteranion with which it was paired.
Specifically, Gnd+ was depleted from the ELP/water interface
and was found to stabilize the collapsed state of the macromolecule
when paired with well-hydrated anions such as SO42–. Stabilization in this case occurred via an excluded volume (or
depletion) effect, whereby SO42– was
strongly partitioned away from the ELP/water interface. Intriguingly,
at low salt concentrations, Gnd+ was also found to stabilize
the collapsed state of the ELP when paired with SCN–, which is a strong binder for the ELP. In this case, the anion and
cation were both found to be enriched in the collapsed state of the
polymer. The collapsed state was favored because the Gnd+ cross-linked the polymer chains together. Moreover, the anion helped
partition Gnd+ to the polymer surface. At higher salt concentrations
(>1.5 M), GndSCN switched to stabilizing the uncollapsed state
because
a sufficient amount of Gnd+ and SCN– partitioned
to the polymer surface to prevent cross-linking from occurring. Finally,
in a third case, it was found that salts which interacted in an intermediate
fashion with the polymer (e.g., GndCl) favored the uncollapsed conformation
at all salt concentrations. These results provide a detailed, molecular-level,
mechanistic picture of how Gnd+ influences the stability
of polypeptides in three distinct physical regimes by varying the
anion. It also helps explain the circumstances under which guanidinium
salts can act as powerful and versatile protein denaturants.
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Affiliation(s)
- Jan Heyda
- Institut für Weiche Materie und Funktionale Materialien, Helmholtz-Zentrum Berlin für Materialien und Energie , Hahn-Meitner Platz 1, 14109 Berlin, Germany.,Physical Chemistry Department, University of Chemistry and Technology, Prague , Technicka 5, 16628 Prague 6, Czech Republic
| | | | - Jana Hladílková
- Division of Theoretical Chemistry, Lund University , POB 124, 22 100 Lund, Sweden.,Institute of Organic Chemistry and Biochemistry, Academy of Sciences of the Czech Republic , Flemingovo nám. 2, 16610 Prague 6, Czech Republic
| | | | - William Hunn
- Chemistry Department, Texas A&M University , 3255 TAMU, College Station, Texas 77843, United States
| | | | - Joachim Dzubiella
- Institut für Weiche Materie und Funktionale Materialien, Helmholtz-Zentrum Berlin für Materialien und Energie , Hahn-Meitner Platz 1, 14109 Berlin, Germany.,Institut für Physik, Humboldt-Universität zu Berlin , Newtonstr. 15, 12489 Berlin, Germany
| | - Pavel Jungwirth
- Institute of Organic Chemistry and Biochemistry, Academy of Sciences of the Czech Republic , Flemingovo nám. 2, 16610 Prague 6, Czech Republic
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5
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Zhang J, Frey V, Corcoran M, Zhang-van Enk J, Subramony JA. Influence of Arginine Salts on the Thermal Stability and Aggregation Kinetics of Monoclonal Antibody: Dominant Role of Anions. Mol Pharm 2016; 13:3362-3369. [DOI: 10.1021/acs.molpharmaceut.6b00255] [Citation(s) in RCA: 21] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- Jifeng Zhang
- Department
of Drug Device and Delivery Development, Biopharmaceutical Development, MedImmune LLC, Gaithersburg, Maryland 20878, United States
| | - Vadim Frey
- Department
of Drug Device and Delivery Development, Biopharmaceutical Development, MedImmune LLC, Gaithersburg, Maryland 20878, United States
| | - Marta Corcoran
- Department
of Drug Device and Delivery Development, Biopharmaceutical Development, MedImmune LLC, Gaithersburg, Maryland 20878, United States
| | - Jian Zhang-van Enk
- Cura Point LLC, 2000 Cal Young Road,
Suite D, Eugene, Oregon 97401, United States
| | - J. Anand Subramony
- Department
of Drug Device and Delivery Development, Biopharmaceutical Development, MedImmune LLC, Gaithersburg, Maryland 20878, United States
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6
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Meuzelaar H, Panman MR, Woutersen S. Guanidinium-Induced Denaturation by Breaking of Salt Bridges. Angew Chem Int Ed Engl 2015. [DOI: 10.1002/ange.201508601] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/05/2022]
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7
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Meuzelaar H, Panman MR, Woutersen S. Guanidinium-Induced Denaturation by Breaking of Salt Bridges. Angew Chem Int Ed Engl 2015; 54:15255-9. [DOI: 10.1002/anie.201508601] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/14/2015] [Indexed: 11/11/2022]
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8
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Heiles S, Cooper RJ, DiTucci MJ, Williams ER. Hydration of guanidinium depends on its local environment. Chem Sci 2015; 6:3420-3429. [PMID: 28706704 PMCID: PMC5490459 DOI: 10.1039/c5sc00618j] [Citation(s) in RCA: 21] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/17/2015] [Accepted: 04/14/2015] [Indexed: 01/10/2023] Open
Abstract
Hydration of gaseous guanidinium (Gdm+) with up to 100 water molecules attached was investigated using infrared photodissociation spectroscopy in the hydrogen stretch region between 2900 and 3800 cm-1. Comparisons to IR spectra of low-energy computed structures indicate that at small cluster size, water interacts strongly with Gdm+ with three inner shell water molecules each accepting two hydrogen bonds from adjacent NH2 groups in Gdm+. Comparisons to results for tetramethylammonium (TMA+) and Na+ enable structural information for larger clusters to be obtained. The similarity in the bonded OH region for Gdm(H2O)20+vs. Gdm(H2O)100+ and the similarity in the bonded OH regions between Gdm+ and TMA+ but not Na+ for clusters with <50 water molecules indicate that Gdm+ does not significantly affect the hydrogen-bonding network of water molecules at large size. These results indicate that the hydration around Gdm+ changes for clusters with more than about eight water molecules to one in which inner shell water molecules only accept a single H-bond from Gdm+. More effective H-bonding drives this change in inner-shell water molecule binding to other water molecules. These results show that hydration of Gdm+ depends on its local environment, and that Gdm+ will interact with water even more strongly in an environment where water is partially excluded, such as the surface of a protein. This enhanced hydration in a limited solvation environment may provide new insights into the effectiveness of Gdm+ as a protein denaturant.
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Affiliation(s)
- Sven Heiles
- Department of Chemistry , University of California , B42 Hildebrand Hall , Berkeley , CA 94720 , USA .
| | - Richard J Cooper
- Department of Chemistry , University of California , B42 Hildebrand Hall , Berkeley , CA 94720 , USA .
| | - Matthew J DiTucci
- Department of Chemistry , University of California , B42 Hildebrand Hall , Berkeley , CA 94720 , USA .
| | - Evan R Williams
- Department of Chemistry , University of California , B42 Hildebrand Hall , Berkeley , CA 94720 , USA .
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9
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Cooper RJ, Heiles S, DiTucci MJ, Williams ER. Hydration of Guanidinium: Second Shell Formation at Small Cluster Size. J Phys Chem A 2014; 118:5657-66. [DOI: 10.1021/jp506429a] [Citation(s) in RCA: 21] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/10/2023]
Affiliation(s)
- Richard J. Cooper
- Department
of Chemistry, University of California, Berkeley, California 94720-1460, United States
| | - Sven Heiles
- Department
of Chemistry, University of California, Berkeley, California 94720-1460, United States
| | - Matthew J. DiTucci
- Department
of Chemistry, University of California, Berkeley, California 94720-1460, United States
| | - Evan R. Williams
- Department
of Chemistry, University of California, Berkeley, California 94720-1460, United States
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10
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Shao Q. The addition of 2,2,2-trifluoroethanol prevents the aggregation of guanidinium around protein and impairs its denaturation ability: A molecular dynamics simulation study. Proteins 2013; 82:944-53. [DOI: 10.1002/prot.24468] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/24/2013] [Revised: 09/29/2013] [Accepted: 10/29/2013] [Indexed: 11/08/2022]
Affiliation(s)
- Qiang Shao
- Drug Discovery and Design Center; Shanghai Institute of Materia Medica; Chinese Academy of Sciences; Shanghai 201203 China
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11
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Xie W, Liu C, Yang L, Gao Y. On the molecular mechanism of ion specific Hofmeister series. Sci China Chem 2013. [DOI: 10.1007/s11426-013-5019-1] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/23/2022]
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12
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Hunger J, Neueder R, Buchner R, Apelblat A. A Conductance Study of Guanidinium Chloride, Thiocyanate, Sulfate, and Carbonate in Dilute Aqueous Solutions: Ion-Association and Carbonate Hydrolysis Effects. J Phys Chem B 2013; 117:615-22. [DOI: 10.1021/jp311425v] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/18/2023]
Affiliation(s)
- Johannes Hunger
- Institut für Physikalische und Theoretische Chemie, Universität Regensburg, 93040 Regensburg, Germany
- Max Planck Institute for Polymer Research, Ackermannweg 10, 55128 Mainz,
Germany
| | - Roland Neueder
- Institut für Physikalische und Theoretische Chemie, Universität Regensburg, 93040 Regensburg, Germany
| | - Richard Buchner
- Institut für Physikalische und Theoretische Chemie, Universität Regensburg, 93040 Regensburg, Germany
| | - Alexander Apelblat
- Department of Chemical
Engineering, Ben-Gurion University of the Negev, 84105 Beer Sheva, Israel
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13
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Mason PE, Neilson GW, Price DL, Saboungi ML, Brady JW. A new structural technique for examining ion-neutral association in aqueous solution. Faraday Discuss 2013; 160:161-70; discussion 207-24. [DOI: 10.1039/c2fd20081c] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
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14
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Shao Q, Fan Y, Yang L, Gao YQ. Counterion Effects on the Denaturing Activity of Guanidinium Cation to Protein. J Chem Theory Comput 2012; 8:4364-73. [DOI: 10.1021/ct3002267] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/11/2023]
Affiliation(s)
- Qiang Shao
- Institute of Theoretical and
Computational Chemistry, College of Chemistry and Molecular Engineering,
Beijing National Laboratory of Molecular Sciences, Peking University, Beijing 100871, China
- Drug Discovery and Design Center,
Shanghai Institute of Materia Medica, Chinese Academy of Sciences, 555 Zuchongzhi Road, Shanghai, 201203,
China
| | - Yubo Fan
- Bioinformatics and
Bioengineering
Program, The Methodist Hospital Research Institute, Weill Cornell Medical College, Houston, Texas 77030, United
States
| | - Lijiang Yang
- Institute of Theoretical and
Computational Chemistry, College of Chemistry and Molecular Engineering,
Beijing National Laboratory of Molecular Sciences, Peking University, Beijing 100871, China
| | - Yi Qin Gao
- Institute of Theoretical and
Computational Chemistry, College of Chemistry and Molecular Engineering,
Beijing National Laboratory of Molecular Sciences, Peking University, Beijing 100871, China
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15
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Mason PE, Wernersson E, Jungwirth P. Accurate Description of Aqueous Carbonate Ions: An Effective Polarization Model Verified by Neutron Scattering. J Phys Chem B 2012; 116:8145-53. [DOI: 10.1021/jp3008267] [Citation(s) in RCA: 48] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- Philip E. Mason
- Institute
of Organic Chemistry and Biochemistry, Academy of Sciences of the Czech Republic, Flemingovo nám. 2, 16610
Prague 6, Czech Republic
| | - Erik Wernersson
- Institute
of Organic Chemistry and Biochemistry, Academy of Sciences of the Czech Republic, Flemingovo nám. 2, 16610
Prague 6, Czech Republic
| | - Pavel Jungwirth
- Institute
of Organic Chemistry and Biochemistry, Academy of Sciences of the Czech Republic, Flemingovo nám. 2, 16610
Prague 6, Czech Republic
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16
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Conley MP, Valero J, de Mendoza J. Guanidinium-Based Receptors for Oxoanions. Supramol Chem 2012. [DOI: 10.1002/9780470661345.smc061] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
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17
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Schneider CP, Shukla D, Trout BL. Effects of solute-solute interactions on protein stability studied using various counterions and dendrimers. PLoS One 2011; 6:e27665. [PMID: 22125620 PMCID: PMC3220676 DOI: 10.1371/journal.pone.0027665] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/14/2011] [Accepted: 10/21/2011] [Indexed: 11/19/2022] Open
Abstract
Much work has been performed on understanding the effects of additives on protein thermodynamics and degradation kinetics, in particular addressing the Hofmeister series and other broad empirical phenomena. Little attention, however, has been paid to the effect of additive-additive interactions on proteins. Our group and others have recently shown that such interactions can actually govern protein events, such as aggregation. Here we use dendrimers, which have the advantage that both size and surface chemical groups can be changed and therein studied independently. Dendrimers are a relatively new and broad class of materials which have been demonstrated useful in biological and therapeutic applications, such as drug delivery, perturbing amyloid formation, etc. Guanidinium modified dendrimers pose an interesting case given that guanidinium can form multiple attractive hydrogen bonds with either a protein surface or other components in solution, such as hydrogen bond accepting counterions. Here we present a study which shows that the behavior of such macromolecule species (modified PAMAM dendrimers) is governed by intra-solvent interactions. Attractive guanidinium-anion interactions seem to cause clustering in solution, which inhibits cooperative binding to the protein surface but at the same time, significantly suppresses nonnative aggregation.
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Affiliation(s)
- Curtiss P. Schneider
- Department of Chemical Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts, United States of America
| | - Diwakar Shukla
- Department of Chemical Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts, United States of America
| | - Bernhardt L. Trout
- Department of Chemical Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts, United States of America
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Shukla D, Schneider CP, Trout BL. Complex Interactions between Molecular Ions in Solution and Their Effect on Protein Stability. J Am Chem Soc 2011; 133:18713-8. [DOI: 10.1021/ja205215t] [Citation(s) in RCA: 34] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022]
Affiliation(s)
- Diwakar Shukla
- Department of Chemical Engineering, Massachusetts Institute of Technology, E19-502b, 77 Massachusetts Avenue, Cambridge, Massachusetts 02139, United States
| | - Curtiss P. Schneider
- Department of Chemical Engineering, Massachusetts Institute of Technology, E19-502b, 77 Massachusetts Avenue, Cambridge, Massachusetts 02139, United States
| | - Bernhardt L. Trout
- Department of Chemical Engineering, Massachusetts Institute of Technology, E19-502b, 77 Massachusetts Avenue, Cambridge, Massachusetts 02139, United States
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Shukla D, Schneider CP, Trout BL. Molecular level insight into intra-solvent interaction effects on protein stability and aggregation. Adv Drug Deliv Rev 2011; 63:1074-85. [PMID: 21762737 DOI: 10.1016/j.addr.2011.06.014] [Citation(s) in RCA: 70] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/11/2011] [Revised: 06/14/2011] [Accepted: 06/29/2011] [Indexed: 11/16/2022]
Abstract
Protein based therapeutics hold great promise in the treatment of human diseases and disorders and subsequently, they have become the fastest growing sector of new drugs being developed. Proteins are, however, inherently unstable and the degraded form can be quite harmful if administered to a patient. Of the various degradation pathways, aggregation is one of the most common and a cause for great concern. Aggregation suppressing additives have long been used to stabilize proteins, and they still remain the most viable option for combating this problem. Much work has been devoted toward investigating the behavior of commonly used additives and the resulting models give valuable insight toward explaining aggregation suppression. In a few cases, an explanation for unique behavior is lacking or new insight provides an alternate explanation. Additive selection and the development of better performing additives may benefit from a more refined understanding of how commonly used additives inhibit or enhance aggregation. In this review, we focus on recent molecular-level studies into how a select group of commonly used additives interact with proteins and subsequently influence aggregation. The intent of the review is not meant to be comprehensive for each additive but rather to provide new insights into additive-additive interactions, which may be contributing to protein-additive interactions. This is something that is often overlooked but yet essential to understanding the effect of additives on aggregation. The importance of understanding such interactions is clear when one considers that most formulations contain a mixture of cosolutes and that ideal stability might be better achieved through tuning intra-solvent interactions. We give an example of this when we describe how novel aggregation suppressing additives were developed from the knowledge gained from the reviewed studies.
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Affiliation(s)
- Diwakar Shukla
- Department of Chemical Engineering, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, MA 02139, USA
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20
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Graziano G. Contrasting the denaturing effect of guanidinium chloride with the stabilizing effect of guanidinium sulfate. Phys Chem Chem Phys 2011; 13:12008-14. [PMID: 21617819 DOI: 10.1039/c1cp20843h] [Citation(s) in RCA: 49] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Guanidinium chloride, GdmCl, is a strong denaturing agent of globular proteins, whereas guanidinium sulfate, Gdm(2)SO(4), is a stabilizing agent of globular proteins. The stabilizing activity of Gdm(2)SO(4) is unexpected because the denaturant capability of GdmCl is due to direct interactions of Gdm(+) ions with protein surface groups. It is shown that the statistical thermodynamic approach devised to explain the molecular origin of cold denaturation [G. Graziano, Phys. Chem. Chem. Phys., 2010, 12, 14245-14252] can provide a rationalization of the different behaviour of GdmCl and Gdm(2)SO(4) towards globular proteins. The fundamental quantity is the reversible work to create in the aqueous solution a cavity suitable to host the D-state and a cavity suitable to host the N-state. In aqueous GdmCl solutions, this contribution is not large enough to overwhelm the conformational entropy gain upon unfolding and the direct attractions between Gdm(+) ions and protein surface groups; in aqueous Gdm(2)SO(4) solutions, it is so large that it overwhelms the two destabilizing contributions. Sulfate ions, due to their high charge density, interact strongly with water molecules producing a number density increase, that, in turn, renders the cavity creation process very costly, reversing the denaturing power of Gdm(+) ions and stabilizing the N-state of globular proteins.
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Affiliation(s)
- Giuseppe Graziano
- Dipartimento di Scienze Biologiche ed Ambientali, Università del Sannio, Via Port'Arsa 11-82100 Benevento, Italy.
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21
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Schneider CP, Shukla D, Trout BL. Arginine and the Hofmeister Series: the role of ion-ion interactions in protein aggregation suppression. J Phys Chem B 2011; 115:7447-58. [PMID: 21568311 DOI: 10.1021/jp111920y] [Citation(s) in RCA: 104] [Impact Index Per Article: 8.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022]
Abstract
L-Arginine hydrochloride is a very important aggregation suppressor for which there has been much attention given regarding elucidating its mechanism of action. Little consideration, however, has been given toward other salt forms besides chloride, even though the counterion likely imparts a large influence per the Hofmeister Series. Here, we report an in depth analysis of the role the counterion plays in the aggregation suppression behavior of arginine. Consistent with the empirical Hofmeister series, we found that the aggregation suppression ability of other arginine salt forms on a model protein (α-chymotrypsinogen) follows the order: H(2)PO(4)(-) > SO(4)(2-) > citrate(2-) > acetate(-) ≈ F(-) ≈ Cl(-) > Br(-) > I(-) ≈ SCN(-). Mechanistically, preferential interaction and osmotic virial coefficient measurements, in addition to molecular dynamics simulations, indicate that attractive ion-ion interactions, particularly attractive interactions between arginine molecules, play a dominate role in the observed behavior. Furthermore, it appears that dihydrogen phosphate, sulfate, and citrate have strong attractive interactions with the guanidinium group of arginine, which seems to contribute to the superior aggregation suppression ability of those salt forms by bridging together multiple arginine molecules into clusters. These results not only further our understanding of how arginine influences protein stability, they also help to elucidate the mechanism behind the Hofmeister Series. This should help to improve biopharmaceutical stabilization through the use of other arginine salts and possibly, the development of novel excipients.
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Affiliation(s)
- Curtiss P Schneider
- Department of Chemical Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, United States
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22
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Dempsey CE, Mason PE, Jungwirth P. Complex Ion Effects on Polypeptide Conformational Stability: Chloride and Sulfate Salts of Guanidinium and Tetrapropylammonium. J Am Chem Soc 2011; 133:7300-3. [DOI: 10.1021/ja201349g] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
| | - Philip E. Mason
- Department of Food Science, Cornell University, Ithaca, New York 14853, United States
| | - Pavel Jungwirth
- Institute of Organic Chemistry and Biochemistry, Academy of Sciences of the Czech Republic, and Center for Biomolecules and Complex Molecular Systems, 16610 Prague 6, Czech Republic
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Santiveri CM, Jiménez MA. Tryptophan residues: scarce in proteins but strong stabilizers of β-hairpin peptides. Biopolymers 2011; 94:779-90. [PMID: 20564027 DOI: 10.1002/bip.21436] [Citation(s) in RCA: 77] [Impact Index Per Article: 5.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
Abstract
Tryptophan plays important roles in protein stability and recognition despite its scarcity in proteins. Except as fluorescent groups, they have been used rarely in peptide design. Nevertheless, Trp residues were crucial for the stability of some designed minimal proteins. In 2000, Trp-Trp pairs were shown to contribute more than any other hydrophobic interaction to the stability of β-hairpin peptides. Since then, Trp-Trp pairs have emerged as a paradigm for the design of stable β-hairpins, such as the Trpzip peptides. Here, we analyze the nature of the stabilizing capacity of Trp-Trp pairs by reviewing the β-hairpin peptides containing Trp-Trp pairs described up to now, the spectroscopic features and geometry of the Trp-Trp pairs, and their use as binding sites in β-hairpin peptides. To complete the overview, we briefly go through the other relevant β-hairpin stabilizing Trp-non-Trp interactions and illustrate the use of Trp in the design of short peptides adopting α-helical and mixed α/β motifs. This review is of interest in the field of rational design of proteins, peptides, peptidomimetics, and biomaterials.
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Affiliation(s)
- Clara M Santiveri
- Instituto de Química Física Rocasolano, CSIC, Serrano 119, Madrid 28006, Spain
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24
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Wernersson E, Heyda J, Kubícková A, Krízek T, Coufal P, Jungwirth P. Effect of association with sulfate on the electrophoretic mobility of polyarginine and polylysine. J Phys Chem B 2011; 114:11934-41. [PMID: 20726540 DOI: 10.1021/jp1054342] [Citation(s) in RCA: 38] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Domains rich in cationic amino acids are ubiquitous in peptides with the ability to cross cell membranes, which is likely related to the binding of such polypeptides to anionic groups on the membrane surface. To shed more light on these interactions, we investigated specific interactions between basic amino acids and oligopeptides thereof and anions by means of electrophoretic experiments and molecular dynamics simulations. To this end, we measured the electrophoretic mobilities of arginine, lysine, tetraarginine, and tetralysine in sodium chloride and sodium sulfate electrolytes as a function of ionic strength. The mobility was found to be consistently lower in sodium sulfate than in sodium chloride at the same ionic strength. The decrease in mobility in sodium sulfate was greater for tetraarginine than for tetralysine and was larger for tetrapeptides compared to the corresponding free amino acids. On the basis of molecular dynamics simulations and Bjerrum theory, we rationalize these results in terms of enhanced association between the amino acid side chains and sulfate. Simulations also predict a greater affinity of sulfate to the guanidinium side chain groups of arginine than to the ammonium groups of lysine, as the planar guanidinium geometry allows simultaneous strong hydrogen bonding to two sulfate oxygens. We show that the sulfate binding to arginine, but not to lysine, is cooperative. These results are consistent with the greater decrease in the mobility of arginine compared to that of lysine upon addition of sulfate salt. The nonspecific mobility retardation by sulfate is ascribed to its electrostatic interaction with the cationic amino acid side chain groups.
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Affiliation(s)
- Erik Wernersson
- Institute of Organic Chemistry and Biochemistry, Academy of Sciences of the Czech Republic, and Center for Biomolecules and Complex Molecular Systems, Flemingovo nám. 2, 16610 Prague 6, Czech Republic
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25
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Mason PE, Heyda J, Fischer HE, Jungwirth P. Specific Interactions of Ammonium Functionalities in Amino Acids with Aqueous Fluoride and Iodide. J Phys Chem B 2010; 114:13853-60. [DOI: 10.1021/jp104840g] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Affiliation(s)
- Philip E. Mason
- Department of Food Science, Cornell University, Ithaca, New York 14853, Institute of Organic Chemistry and Biochemistry, Academy of Sciences of the Czech Republic and Center for Biomolecules and Complex Molecular Systems, Flemingovo nam. 2, 16610 Prague 6, Czech Republic, and Institut Laue-Langevin, 6 rue Jules Horowitz, BP 156, Grenoble Cedex 9 F-38042, France
| | - Jan Heyda
- Department of Food Science, Cornell University, Ithaca, New York 14853, Institute of Organic Chemistry and Biochemistry, Academy of Sciences of the Czech Republic and Center for Biomolecules and Complex Molecular Systems, Flemingovo nam. 2, 16610 Prague 6, Czech Republic, and Institut Laue-Langevin, 6 rue Jules Horowitz, BP 156, Grenoble Cedex 9 F-38042, France
| | - Henry E. Fischer
- Department of Food Science, Cornell University, Ithaca, New York 14853, Institute of Organic Chemistry and Biochemistry, Academy of Sciences of the Czech Republic and Center for Biomolecules and Complex Molecular Systems, Flemingovo nam. 2, 16610 Prague 6, Czech Republic, and Institut Laue-Langevin, 6 rue Jules Horowitz, BP 156, Grenoble Cedex 9 F-38042, France
| | - Pavel Jungwirth
- Department of Food Science, Cornell University, Ithaca, New York 14853, Institute of Organic Chemistry and Biochemistry, Academy of Sciences of the Czech Republic and Center for Biomolecules and Complex Molecular Systems, Flemingovo nam. 2, 16610 Prague 6, Czech Republic, and Institut Laue-Langevin, 6 rue Jules Horowitz, BP 156, Grenoble Cedex 9 F-38042, France
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26
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Godawat R, Jamadagni SN, Garde S. Unfolding of hydrophobic polymers in guanidinium chloride solutions. J Phys Chem B 2010; 114:2246-54. [PMID: 20146543 DOI: 10.1021/jp906976q] [Citation(s) in RCA: 64] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Guanidinium chloride (GdmCl) is a widely used chemical denaturant that unfolds proteins. Its effects on hydrophobic interactions are, however, not fully understood. We quantify the effects of GdmCl on various manifestations of hydrophobicity--from solvation and interactions of small solutes to folding-unfolding of hydrophobic polymers--in water and in concentrated GdmCl solutions. For comparison, we also perform similar calculations in solutions of NaCl and CsCl in water. Like NaCl and CsCl, GdmCl increases the surface tension of water, decreases the solubility of small hydrophobic solutes, and enhances the strength of hydrophobic interactions at the pair level. However, unlike NaCl and CsCl, GdmCl destabilizes folded states of hydrophobic polymers. We show that Gdm(+) ions preferentially coat the hydrophobic polymer, and it is the direct van der Waals interaction between Gdm(+) ions and the polymer that contributes to the destabilization of folded states. Interestingly, the temperature dependence of the free energy of unfolding of the hydrophobic polymer in water is protein-like, with signatures of both heat and cold denaturation. Addition of GdmCl shifts the cold denaturation temperature higher, into the experimentally accessible region. Finally, translational as well as conformational dynamics of the polymer are slower in GdmCl and correlate with dynamics of water molecules in solution.
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Affiliation(s)
- Rahul Godawat
- The Howard P. Isermann Department of Chemical & Biological Engineering, and Center for Biotechnology and Interdisciplinary Studies, Rensselaer Polytechnic Institute, Troy, New York 12180, USA
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27
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Mason PE, Dempsey CE, Neilson GW, Kline SR, Brady JW. Preferential interactions of guanidinum ions with aromatic groups over aliphatic groups. J Am Chem Soc 2010; 131:16689-96. [PMID: 19874022 DOI: 10.1021/ja903478s] [Citation(s) in RCA: 66] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Small angle neutron scattering (SANS) and molecular dynamics (MD) simulations were used to characterize the long-range structuring (aggregation) of aqueous solutions of isopropanol (IPA) and pyridine and the effect on structuring of guanidinium chloride (GdmCl). These solutes serve as highly soluble analogs of the nonpolar aliphatic (IPA) and aromatic (pyridine) side chains of proteins. SANS data showed that isopropanol and pyridine both form clusters in water resulting from interaction between nonpolar groups of the solutes, with pyridine aggregation producing longer-range structuring than isopropanol in 3 m solutions. Addition of GdmCl at 3 m concentration considerably reduced pyridine aggregation but had no effect on isopropanol aggregation. MD simulations of these solutions support the conclusion that long-range structuring involves hydrophobic solute interactions and that Gdm(+) interacts with the planar pyridine group to suppress pyridine-pyridine interactions in solution. Hydrophobic interactions involving the aliphatic groups of isopropanol were unaffected by GdmCl, indicating that the planar and weakly hydrated Gdm(+) cation cannot make productive interactions with the highly curved or "lumpy" aliphatic groups of this solute. These observations support the conclusion that the effects of Gdm(+) ions on protein-stabilizing interactions involving aromatic amino acid side chains make significant contributions to the denaturant activity of GdmCl, whereas interactions with the "lumpy" aliphatic side chains are likely to be less important.
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Affiliation(s)
- Philip E Mason
- Department of Food Science, Cornell University, Ithaca, New York 14853, USA
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28
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Jungwirth P. Spiers Memorial Lecture. Ions at aqueous interfaces. Faraday Discuss 2009; 141:9-30; discussion 81-98. [PMID: 19227348 DOI: 10.1039/b816684f] [Citation(s) in RCA: 61] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Studies of aqueous interfaces and of the behavior of ions therein have been profiting from a recent remarkable progress in surface selective spectroscopies, as well as from developments in molecular simulations. Here, we summarize and place in context our investigations of ions at aqueous interfaces employing molecular dynamics simulations and electronic structure methods, performed in close contact with experiment. For the simplest of these interfaces, i.e. the open water surface, we demonstrate that the traditional picture of an ion-free surface is not valid for large, soft (polarizable) ions such as the heavier halides. Both simulations and spectroscopic measurements indicate that these ions can be present and even enhanced at surface of water. In addition we show that the ionic product of water exhibits a peculiar surface behavior with hydronium but not hydroxide accumulating at the air/water and alkane/water interfaces. This result is supported by surface-selective spectroscopic experiments and surface tension measurements. However, it contradicts the interpretation of electrophoretic and titration experiments in terms of strong surface adsorption of hydroxide; an issue which is further discussed here. The applicability of the observed behavior of ions at the water surface to investigations of their affinity for the interface between proteins and aqueous solutions is explored. Simulations show that for alkali cations the dominant mechanism of specific interactions with the surface of hydrated proteins is via ion pairing with negatively charged amino acid residues and with the backbone amide groups. As far as halide anions are concerned, the lighter ones tend to pair with positively charged amino acid residues, while heavier halides exhibit affinity to the amide group and to non-polar protein patches, the latter resembling their behavior at the air/water interface. These findings, together with results for more complex molecular ions, allow us to formulate a local model of interactions of ions with proteins with the aim to rationalize at the molecular level ion-specific Hofmeister effects, e.g. the salting out of proteins.
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Affiliation(s)
- Pavel Jungwirth
- Institute of Organic Chemistry and Biochemistry, Academy of Sciences of the Czech Republic and Center for Complex Molecular Systems and Biomolecules, Prague, Czech Republic.
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29
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Mason PE, Dempsey CE, Vrbka L, Heyda J, Brady JW, Jungwirth P. Specificity of Ion−Protein Interactions: Complementary and Competitive Effects of Tetrapropylammonium, Guanidinium, Sulfate, and Chloride Ions. J Phys Chem B 2009; 113:3227-34. [DOI: 10.1021/jp8112232] [Citation(s) in RCA: 62] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- Philip E. Mason
- Department of Food Science, Cornell University, Ithaca, New York 14853, Department of Biochemistry, Bristol University, Bristol BS8 1TD, U.K., Institute of Organic Chemistry and Biochemistry, Academy of Sciences of the Czech Republic and Center for Biomolecules and Complex Molecular Systems, Flemingovo nám. 2, 16610 Prague 6, Czech Republic, and Institute of Physical and Theoretical Chemistry, University of Regensburg, 93040 Regensburg, Germany
| | - Christopher E. Dempsey
- Department of Food Science, Cornell University, Ithaca, New York 14853, Department of Biochemistry, Bristol University, Bristol BS8 1TD, U.K., Institute of Organic Chemistry and Biochemistry, Academy of Sciences of the Czech Republic and Center for Biomolecules and Complex Molecular Systems, Flemingovo nám. 2, 16610 Prague 6, Czech Republic, and Institute of Physical and Theoretical Chemistry, University of Regensburg, 93040 Regensburg, Germany
| | - Luboš Vrbka
- Department of Food Science, Cornell University, Ithaca, New York 14853, Department of Biochemistry, Bristol University, Bristol BS8 1TD, U.K., Institute of Organic Chemistry and Biochemistry, Academy of Sciences of the Czech Republic and Center for Biomolecules and Complex Molecular Systems, Flemingovo nám. 2, 16610 Prague 6, Czech Republic, and Institute of Physical and Theoretical Chemistry, University of Regensburg, 93040 Regensburg, Germany
| | - Jan Heyda
- Department of Food Science, Cornell University, Ithaca, New York 14853, Department of Biochemistry, Bristol University, Bristol BS8 1TD, U.K., Institute of Organic Chemistry and Biochemistry, Academy of Sciences of the Czech Republic and Center for Biomolecules and Complex Molecular Systems, Flemingovo nám. 2, 16610 Prague 6, Czech Republic, and Institute of Physical and Theoretical Chemistry, University of Regensburg, 93040 Regensburg, Germany
| | - John W. Brady
- Department of Food Science, Cornell University, Ithaca, New York 14853, Department of Biochemistry, Bristol University, Bristol BS8 1TD, U.K., Institute of Organic Chemistry and Biochemistry, Academy of Sciences of the Czech Republic and Center for Biomolecules and Complex Molecular Systems, Flemingovo nám. 2, 16610 Prague 6, Czech Republic, and Institute of Physical and Theoretical Chemistry, University of Regensburg, 93040 Regensburg, Germany
| | - Pavel Jungwirth
- Department of Food Science, Cornell University, Ithaca, New York 14853, Department of Biochemistry, Bristol University, Bristol BS8 1TD, U.K., Institute of Organic Chemistry and Biochemistry, Academy of Sciences of the Czech Republic and Center for Biomolecules and Complex Molecular Systems, Flemingovo nám. 2, 16610 Prague 6, Czech Republic, and Institute of Physical and Theoretical Chemistry, University of Regensburg, 93040 Regensburg, Germany
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30
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Pednekar D, Tendulkar A, Durani S. Electrostatics-defying interaction between arginine termini as a thermodynamic driving force in protein-protein interaction. Proteins 2009; 74:155-63. [PMID: 18618701 DOI: 10.1002/prot.22142] [Citation(s) in RCA: 50] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/05/2022]
Abstract
Apparent electrostatics-defying clustering of arginines attributed as screening effect of solvent is in this study examined as a possible thermodynamic driving force in protein-protein interaction. A dataset of 266 protein dimers is found to have approximately 22% arginines mutually paired and approximately 17% pairs in interaction across interfaces and thus putative "hotspots" of protein-protein interaction. The pairing, uncorrelated with inter or intramolecular context, could be contributing in protein folding as well, and, uncorrelated with solvent access, could be driven by effects that are generic to solvent and protein structures. Mutually stacked at shorter distances but in diverse geometrical modes otherwise, the cations tend to be in gross deficit of hydrogen-bond partners, and contributing electrostatics across protein-protein interface that, on average, is repulsive for protein-protein interaction. Embedded in local environment enriched in polarizable residues, aromatic, aliphatic, and anionic, the arginines may contribute to protein-protein interaction via environmental polarization response to electrostatics of cation clustering, a possible new principle in molecular recognition.
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Affiliation(s)
- Deepa Pednekar
- School of Biosciences and Bioengineering, Indian Institute of Technology Bombay, Mumbai 400076, India
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31
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Takekiyo T, Wu L, Yoshimura Y, Shimizu A, Keiderling TA. Relationship between Hydrophobic Interactions and Secondary Structure Stability for Trpzip β-Hairpin Peptides. Biochemistry 2009; 48:1543-52. [DOI: 10.1021/bi8019838] [Citation(s) in RCA: 51] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Affiliation(s)
- Takahiro Takekiyo
- Department of Chemistry, University of Illinois at Chicago, 845 West Taylor Street, Chicago, Illinois 60607-7061, Department of Applied Chemistry, National Defense Academy, 1-10-20, Hashirimizu, Yokosuka, Kanagawa 239-8686, Japan, and Department of Environmental Engineering for Symbiosis Factory of Engineering, Soka University, 1-236 Tangi-cho, Hachioji, Tokyo 192-8577, Japan
| | - Ling Wu
- Department of Chemistry, University of Illinois at Chicago, 845 West Taylor Street, Chicago, Illinois 60607-7061, Department of Applied Chemistry, National Defense Academy, 1-10-20, Hashirimizu, Yokosuka, Kanagawa 239-8686, Japan, and Department of Environmental Engineering for Symbiosis Factory of Engineering, Soka University, 1-236 Tangi-cho, Hachioji, Tokyo 192-8577, Japan
| | - Yukihiro Yoshimura
- Department of Chemistry, University of Illinois at Chicago, 845 West Taylor Street, Chicago, Illinois 60607-7061, Department of Applied Chemistry, National Defense Academy, 1-10-20, Hashirimizu, Yokosuka, Kanagawa 239-8686, Japan, and Department of Environmental Engineering for Symbiosis Factory of Engineering, Soka University, 1-236 Tangi-cho, Hachioji, Tokyo 192-8577, Japan
| | - Akio Shimizu
- Department of Chemistry, University of Illinois at Chicago, 845 West Taylor Street, Chicago, Illinois 60607-7061, Department of Applied Chemistry, National Defense Academy, 1-10-20, Hashirimizu, Yokosuka, Kanagawa 239-8686, Japan, and Department of Environmental Engineering for Symbiosis Factory of Engineering, Soka University, 1-236 Tangi-cho, Hachioji, Tokyo 192-8577, Japan
| | - Timothy A. Keiderling
- Department of Chemistry, University of Illinois at Chicago, 845 West Taylor Street, Chicago, Illinois 60607-7061, Department of Applied Chemistry, National Defense Academy, 1-10-20, Hashirimizu, Yokosuka, Kanagawa 239-8686, Japan, and Department of Environmental Engineering for Symbiosis Factory of Engineering, Soka University, 1-236 Tangi-cho, Hachioji, Tokyo 192-8577, Japan
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