1
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Dinic J, Tirrell MV. Effects of Charge Sequence Pattern and Lysine-to-Arginine Substitution on the Structural Stability of Bioinspired Polyampholytes. Biomacromolecules 2024; 25:2838-2851. [PMID: 38567844 PMCID: PMC11094733 DOI: 10.1021/acs.biomac.4c00002] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/01/2024] [Revised: 03/17/2024] [Accepted: 03/18/2024] [Indexed: 05/14/2024]
Abstract
A comprehensive study focusing on the combined influence of the charge sequence pattern and the type of positively charged amino acids on the formation of secondary structures in sequence-specific polyampholytes is presented. The sequences of interest consisting exclusively of ionizable amino acids (lysine, K; arginine, R; and glutamic acid, E) are (EKEK)5, (EKKE)5, (ERER)5, (ERRE)5, and (EKER)5. The stability of the secondary structure was examined at three pH values in the presence of urea and NaCl. The results presented here underscore the combined prominent effects of the charge sequence pattern and the type of positively charged monomers on secondary structure formation. Additionally, (ERRE)5 readily aggregated across a wide range of pH. In contrast, sequences with the same charge pattern, (EKKE)5, as well as the sequences with the equivalent amino acid content, (ERER)5, exhibited no aggregate formation under equivalent pH and concentration conditions.
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Affiliation(s)
- Jelena Dinic
- Pritzker
School of Molecular Engineering, University
of Chicago, Chicago, Illinois 60637, United States
- Center
for Molecular Engineering and Materials Science Division, Argonne National Laboratory, Lemont, Illinois 60439, United States
| | - Matthew V. Tirrell
- Pritzker
School of Molecular Engineering, University
of Chicago, Chicago, Illinois 60637, United States
- Center
for Molecular Engineering and Materials Science Division, Argonne National Laboratory, Lemont, Illinois 60439, United States
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2
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Seelig J, Seelig A. Chemical Protein Unfolding - A Simple Cooperative Model. J Phys Chem B 2023; 127:8296-8304. [PMID: 37735883 PMCID: PMC10561279 DOI: 10.1021/acs.jpcb.3c03558] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/26/2023] [Revised: 08/08/2023] [Indexed: 09/23/2023]
Abstract
Chemical unfolding with guanidineHCl or urea is a common method to study the conformational stability of proteins. The analysis of unfolding isotherms is usually performed with an empirical linear extrapolation method (LEM). A large positive free energy is assigned to the native protein, which is usually considered to be a minimum of the free energy. The method thus contradicts common expectations. Here, we present a multistate cooperative model that addresses specifically the binding of the denaturant to the protein and the cooperativity of the protein unfolding equilibrium. The model is based on a molecular statistical-mechanical partition function of the ensemble, but simple solutions for the calculation of the binding isotherm and the associated free energy are presented. The model is applied to 23 published unfolding isotherms of small and large proteins. For a given denaturant, the binding constant depends on temperature and pH but shows little protein specificity. Chemical unfolding is less cooperative than thermal unfolding. The cooperativity parameter σ is at least 2 orders of magnitude larger than that of thermal unfolding. The multistate cooperative model predicts zero free energy for the native protein, which becomes strongly negative beyond the midpoint concentration of unfolding. The free energy to unfold a cooperative unit corresponds exactly to the diffusive energy of the denaturant concentration gradient necessary for unfolding. The temperature dependence of unfolding isotherms yields the denaturant-induced unfolding entropy and, in turn, the unfolding enthalpy. The multistate cooperative model provides molecular insight and is as simple to apply as the LEM but avoids the conceptual difficulties of the latter.
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Affiliation(s)
- Joachim Seelig
- Biozentrum, University
of Basel, Spitalstrasse 41, CH-4056 Basel, Switzerland
| | - Anna Seelig
- Biozentrum, University
of Basel, Spitalstrasse 41, CH-4056 Basel, Switzerland
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3
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Singh NK, Agarwal M, Radhakrishna M. Understanding the helical stability of charged peptides. Proteins 2023; 91:268-276. [PMID: 36121161 DOI: 10.1002/prot.26427] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/05/2022] [Revised: 08/12/2022] [Accepted: 09/06/2022] [Indexed: 01/10/2023]
Abstract
Cationic helical peptides play a crucial role in applications such as anti-microbial and anticancer activity. The activity of these peptides directly correlates with their helicity. In this study, we have performed extensive all-atom molecular dynamics simulations of 25 Lysine-Leucine co-polypeptide sequences of varying charge density ( λ ) and patterns. Our findings showed that, an increase in the charge density on the peptide leads to a gradual decrease in the helicity up to a critical charge density λ c . Beyond λ c , a complete helix to coil transition was observed. The decrease in the helicity is correlated with the increased number of water molecules in first solvation shell, solvent-exposed surface area, and a higher value of the radius of gyration of the peptide.
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Affiliation(s)
- Nitin Kumar Singh
- Discipline of Chemical Engineering, Indian Institute of Technology (IIT), Gandhinagar, Gujarat, India
| | - Manish Agarwal
- Computer Services Centre, Indian Institute of Technology (IIT), Delhi, India
| | - Mithun Radhakrishna
- Discipline of Chemical Engineering, Indian Institute of Technology (IIT), Gandhinagar, Gujarat, India.,Center for Biomedical Engineering, Indian Institute of Technology (IIT), Gandhinagar, Gujarat, India
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4
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Seelig J, Seelig A. Molecular understanding of calorimetric protein unfolding experiments. BIOPHYSICAL REPORTS 2022; 2:100037. [PMID: 36425081 PMCID: PMC9680786 DOI: 10.1016/j.bpr.2021.100037] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 09/09/2021] [Accepted: 12/02/2021] [Indexed: 06/16/2023]
Abstract
Testing and predicting protein stability gained importance because proteins, including antibodies, became pharmacologically relevant in viral and cancer therapies. Isothermal scanning calorimetry is the principle method to study protein stability. Here, we use the excellent experimental heat capacity Cp(T) data from the literature for a critical inspection of protein unfolding as well as for the test of a new cooperative model. In the relevant literature, experimental temperature profiles of enthalpy, Hcal(T), entropy, Scal(T), and free energy, Gcal(T) are missing. First, we therefore calculate the experimental Hcal(T), Scal(T), and Gcal(T) from published Cp(T) thermograms. Considering only the unfolding transition proper, the heat capacity and all thermodynamic functions are zero in the region of the native protein. In particular, the free energy of the folded proteins is also zero and Gcal(T) displays a trapezoidal temperature profile when cold denaturation is included. Second, we simulate the DSC-measured thermodynamic properties with a new molecular model based on statistical-mechanical thermodynamics. The model quantifies the protein cooperativity and predicts the aggregate thermodynamic variables of the system with molecular parameters only. The new model provides a perfect simulation of all thermodynamic properties, including the observed trapezoidal Gcal(T) temperature profile. Importantly, the new cooperative model can be applied to a broad range of protein sizes, including antibodies. It predicts not only heat and cold denaturation but also provides estimates of the unfolding kinetics and allows a comparison with molecular dynamics calculations and quasielastic neutron scattering experiments.
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Affiliation(s)
| | - Anna Seelig
- Biozentrum, University of Basel, Basel, Switzerland
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5
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Lomize AL, Schnitzer KA, Todd SC, Pogozheva ID. Thermodynamics-Based Molecular Modeling of α-Helices in Membranes and Micelles. J Chem Inf Model 2021; 61:2884-2896. [PMID: 34029472 DOI: 10.1021/acs.jcim.1c00161] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
The Folding of Membrane-Associated Peptides (FMAP) method was developed for modeling α-helix formation by linear peptides in micelles and lipid bilayers. FMAP 2.0 identifies locations of α-helices in the amino acid sequence, generates their three-dimensional models in planar bilayers or spherical micelles, and estimates their thermodynamic stabilities and tilt angles, depending on temperature and pH. The method was tested for 723 peptides (926 data points) experimentally studied in different environments and for 170 single-pass transmembrane (TM) proteins with available crystal structures. FMAP 2.0 detected more than 95% of experimentally observed α-helices with an average error in helix end determination of around 2, 3, 4, and 5 residues per helix for peptides in water, micelles, bilayers, and TM proteins, respectively. Helical and nonhelical residue states were predicted with an accuracy from 0.86 to 0.96, and the Matthews correlation coefficient was from 0.64 to 0.88 depending on the environment. Experimental micelle- and membrane-binding energies and tilt angles of peptides were reproduced with a root-mean-square deviation of around 2 kcal/mol and 7°, respectively. The TM and non-TM states of hydrophobic and pH-triggered α-helical peptides in various lipid bilayers were reproduced in more than 95% of cases. The FMAP 2.0 web server (https://membranome.org/fmap) is publicly available to explore the structural polymorphism of antimicrobial, cell-penetrating, fusion, and other membrane-binding peptides, which is important for understanding the mechanisms of their biological activities.
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Affiliation(s)
- Andrei L Lomize
- Department of Medicinal Chemistry, College of Pharmacy, University of Michigan, 428 Church Street, Ann Arbor, Michigan 48109-1065, United States
| | - Kevin A Schnitzer
- Department of Electrical Engineering and Computer Science, College of Engineering, University of Michigan, 1221 Beal Avenue, Ann Arbor, Michigan 48109-2102, United States
| | - Spencer C Todd
- Department of Electrical Engineering and Computer Science, College of Engineering, University of Michigan, 1221 Beal Avenue, Ann Arbor, Michigan 48109-2102, United States
| | - Irina D Pogozheva
- Department of Medicinal Chemistry, College of Pharmacy, University of Michigan, 428 Church Street, Ann Arbor, Michigan 48109-1065, United States
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6
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Zhuang Y, Bureau HR, Lopez C, Bucher R, Quirk S, Hernandez R. Energetics and structure of alanine-rich α-helices via adaptive steered molecular dynamics. Biophys J 2021; 120:2009-2018. [PMID: 33775636 PMCID: PMC8204395 DOI: 10.1016/j.bpj.2021.03.017] [Citation(s) in RCA: 7] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/30/2020] [Revised: 03/03/2021] [Accepted: 03/18/2021] [Indexed: 12/12/2022] Open
Abstract
The energetics and hydrogen bonding profiles of the helix-to-coil transition were found to be an additive property and to increase linearly with chain length, respectively, in alanine-rich α-helical peptides. A model system of polyalanine repeats was used to establish this hypothesis for the energetic trends and hydrogen bonding profiles. Numerical measurements of a synthesized polypeptide Ac-Y(AEAAKA)kF-NH2 and a natural α-helical peptide a2N (1-17) provide evidence of the hypothesis's generality. Adaptive steered molecular dynamics was employed to investigate the mechanical unfolding of all of these alanine-rich polypeptides. We found that the helix-to-coil transition is primarily dependent on the breaking of the intramolecular backbone hydrogen bonds and independent of specific side-chain interactions and chain length. The mechanical unfolding of the α-helical peptides results in a turnover mechanism in which a 310-helical structure forms during the unfolding, remaining at a near constant population and thereby maintaining additivity in the free energy. The intermediate partially unfolded structures exhibited polyproline II helical structure as previously seen by others. In summary, we found that the average force required to pull alanine-rich α-helical peptides in between the endpoints-namely the native structure and free coil-is nearly independent of the length or the specific primary structure.
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Affiliation(s)
- Yi Zhuang
- Department of Chemistry, Johns Hopkins University, Baltimore, Maryland
| | - Hailey R Bureau
- Department of Chemistry, Johns Hopkins University, Baltimore, Maryland
| | - Christine Lopez
- Department of Chemistry, Johns Hopkins University, Baltimore, Maryland
| | - Ryan Bucher
- Department of Chemistry, Johns Hopkins University, Baltimore, Maryland
| | | | - Rigoberto Hernandez
- Department of Chemistry, Johns Hopkins University, Baltimore, Maryland; Departments of Chemical and Biomolecular Engineering, and Materials Science and Engineering, Johns Hopkins University, Baltimore, Maryland.
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7
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Djajamuliadi J, Ohgo K, Kumashiro KK. A Two-State Model Describes the Temperature-Dependent Conformational Equilibrium in the Alanine-Rich Domains in Elastin. J Phys Chem B 2020; 124:9017-9028. [PMID: 32936634 DOI: 10.1021/acs.jpcb.0c06811] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Elastin is the insoluble elastomeric protein that provides extensibility and resilience to vertebrate tissues. Limited high-resolution structural data for elastin are notably complex. To access this information, this protein is considered in the simplified context of its two general domain types, that is, hydrophobic (HP) and crosslinking (CL). The question of elastin's structure-function has directed the focus of nearly all previous studies in the literature to the unique repeating sequences characteristic of this protein, found primarily in the HP domains. The CL domains were assumed to play a very limited role in biological elasticity due in part to the significant α-helical character that was (incorrectly) predicted for these regions. In this study, the conformational heterogeneity of alanines in native elastin's CL domains is examined in the context of helix-coil transition theory (HCTT) using solid-state nuclear magnetic resonance (SSNMR) spectroscopy in tandem with strategic isotopic labeling. Helix and coil populations are observed at all temperatures, but the former increases significantly at lower temperatures. Below the glass transition temperature (Tg), two major populations of alanines in the CL regions are resolved by two-dimensional SSNMR; one-dimensional methods are used for characterization in nativelike conditions. The spectra of 13CO-Ala in the CL regions are simulated using an HCTT-based statistical mechanical representation. Below Tg, longer segments with significant helical probabilities are consistent with the experimental data. At higher temperatures, the SSNMR lineshapes are best fit with a distribution of shorter (Ala)n segments, most in random coil. These results are used to refine a structure-function model for elastin in the context of HCTT, redirecting attention to the CL domains and their role in elasticity.
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Affiliation(s)
- Jhonsen Djajamuliadi
- Department of Chemistry, University of Hawaii, 2545 McCarthy Mall, Honolulu, Hawaii 96822, United States
| | - Kosuke Ohgo
- Department of Chemistry, University of Hawaii, 2545 McCarthy Mall, Honolulu, Hawaii 96822, United States
| | - Kristin K Kumashiro
- Department of Chemistry, University of Hawaii, 2545 McCarthy Mall, Honolulu, Hawaii 96822, United States
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8
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Garidel P, Eiperle A, Blech M, Seelig J. Thermal and Chemical Unfolding of a Monoclonal IgG1 Antibody: Application of the Multistate Zimm-Bragg Theory. Biophys J 2020; 118:1067-1075. [PMID: 32049058 PMCID: PMC7063443 DOI: 10.1016/j.bpj.2019.12.037] [Citation(s) in RCA: 9] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/03/2019] [Revised: 12/20/2019] [Accepted: 12/30/2019] [Indexed: 11/25/2022] Open
Abstract
The thermal unfolding of a recombinant monoclonal antibody IgG1 (mAb) was measured with differential scanning calorimetry (DSC). The DSC thermograms reveal a pretransition at 72°C with an unfolding enthalpy of ΔHcal ∼200-300 kcal/mol and a main transition at 85°C with an enthalpy of ∼900-1000 kcal/mol. In contrast to small single-domain proteins, mAb unfolding is a complex reaction that is analyzed with the multistate Zimm-Bragg theory. For the investigated mAb, unfolding is characterized by a cooperativity parameter σ ∼6 × 10-5 and a Gibbs free energy of unfolding of gnu ∼100 cal/mol per amino acid. The enthalpy of unfolding provides the number of amino acid residues ν participating in the unfolding reaction. On average, ν∼220 ± 50 amino acids are involved in the pretransition and ν∼850 ± 30 in the main transition, accounting for ∼90% of all amino acids. Thermal unfolding was further studied in the presence of guanidineHCl. The chemical denaturant reduces the unfolding enthalpy ΔHcal and lowers the midpoint temperature Tm. Both parameters depend linearly on the concentration of denaturant. The guanidineHCl concentrations needed to unfold mAb at 25°C are predicted to be 2-3 M for the pretransition and 5-7 M for the main transition, varying with pH. GuanidineHCl binds to mAb with an exothermic binding enthalpy, which partially compensates the endothermic mAb unfolding enthalpy. The number of guanidineHCl molecules bound upon unfolding is deduced from the DSC thermograms. The bound guanidineHCl-to-unfolded amino acid ratio is 0.79 for the pretransition and 0.55 for the main transition. The pretransition binds more denaturant molecules and is more sensitive to unfolding than the main transition. The current study shows the strength of the Zimm-Bragg theory for the quantitative description of unfolding events of large, therapeutic proteins, such as a monoclonal antibody.
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Affiliation(s)
- Patrick Garidel
- Boehringer Ingelheim Pharma GmbH & Co. KG, Innovation Unit, PDB, Biberach an der Riss, Germany.
| | - Andrea Eiperle
- Boehringer Ingelheim Pharma GmbH & Co. KG, Innovation Unit, PDB, Biberach an der Riss, Germany
| | - Michaela Blech
- Boehringer Ingelheim Pharma GmbH & Co. KG, Innovation Unit, PDB, Biberach an der Riss, Germany
| | - Joachim Seelig
- Biozentrum, University of Basel, Klingelbergstrasse 50/70, Basel, Switzerland.
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9
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Structural features of split and unsplit βαβ-units. J Struct Biol 2020; 209:107427. [PMID: 31756457 DOI: 10.1016/j.jsb.2019.107427] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/22/2019] [Revised: 11/06/2019] [Accepted: 11/16/2019] [Indexed: 11/21/2022]
Abstract
In this study, 1064 nonhomologous "unsplit", "one-strand split" and "two-strand split" right-handed βαβ-units having standard α-helices and loops up to seven residues in length have been analyzed. It was found that the α-helices in these kinds of βαβ-units have different distributions of the hydrophobic and hydrophilic amino acid residues along the chain. In the unsplit βαβ-units, most α-helices have hydrophobic residues in positions N4-N7-N8-N11 or N6-N7-N10, where N1 is the first N-terminal residue. In the one-strand split βαβ-units, most α-helices have hydrophobic residues in positions N4-N7-N8-N11 and those in two-strand split βαβ-units in positions N4-N5-N8-N12. On the other hand, in all kinds of βαβ-units, there are commonly occurring hydrophobic stripes of type C4-C7-C8 at the C-terminal parts of the α-helices. As a rule, the C- and N-terminal hydrophobic stripes overlap and the extent of their overlapping determine the length of α-helices.
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10
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Li-Blatter X, Seelig J. Thermal and Chemical Unfolding of Lysozyme. Multistate Zimm-Bragg Theory Versus Two-State Model. J Phys Chem B 2019; 123:10181-10191. [PMID: 31686511 DOI: 10.1021/acs.jpcb.9b08816] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022]
Abstract
Thermal and chemical unfolding of lysozyme in the presence of the guanidine HCl denaturant is a model system to compare the conventional two-state model of protein unfolding with the multistate Zimm-Bragg theory. The two-state model is shown to be the noncooperative limit of the Zimm-Bragg theory. In particular, the Zimm-Bragg theory provides a molecular interpretation of the empirical linear extrapolation method (LEM) of the two-state model. Differential scanning calorimetry (DSC) experiments reported in the literature are analyzed with both methods. Lysozyme unfolding is associated with a large endothermic enthalpy that decreases significantly upon addition of guanidine HCl. In contrast, the Gibbs free energy of unfolding is small, negative, and independent of the guanidine HCl concentration, contradicting, in part, the conclusions of the LEM. The unfolding enthalpy is compensated by an even larger entropy term. The multistate Zimm-Bragg theory predicts a larger conformational enthalpy and a smaller Gibbs free energy than the two-state model. The Zimm-Bragg theory provides the protein cooperativity parameter, the average length of independently folding protein domains, and the Gibbs free energy of unfolding of individual amino acid residues. Guanidine HCl binding to lysozyme is exothermic and counteracts the endothermic unfolding enthalpy. The number of bound denaturant molecules is determined from the decrease in enthalpy and is extrapolated to the guanidine HCl-to-amino acid stoichiometry at complete lysozyme unfolding. Chemical unfolding isotherms measured with circular dichroism (CD) spectroscopy are analyzed with both models. The chemical Zimm-Bragg theory is a cooperative molecular model, yielding the guanidine HCl binding constant and the protein cooperativity parameter. It allows a quantitative comparison between thermal and chemical protein unfolding. The two reactions have almost identical changes in Gibbs free energy. However, thermal unfolding is significantly more cooperative than chemical unfolding. Finally, distinct differences are observed in thermal unfolding between DSC and CD spectroscopy.
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Affiliation(s)
- Xiaochun Li-Blatter
- Biozentrum , University of Basel , Klingelbergstrasse 50/70 , CH-4056 Basel , Switzerland
| | - Joachim Seelig
- Biozentrum , University of Basel , Klingelbergstrasse 50/70 , CH-4056 Basel , Switzerland
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11
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Eckhardt D, Li-Blatter X, Schönfeld HJ, Heerklotz H, Seelig J. Cooperative unfolding of apolipoprotein A-1 induced by chemical denaturation. Biophys Chem 2018; 240:42-49. [DOI: 10.1016/j.bpc.2018.05.005] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/10/2018] [Revised: 05/22/2018] [Accepted: 05/22/2018] [Indexed: 12/30/2022]
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12
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Seelig J. Cooperative protein unfolding. A statistical-mechanical model for the action of denaturants. Biophys Chem 2017; 233:19-25. [PMID: 29232602 DOI: 10.1016/j.bpc.2017.12.001] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/25/2017] [Revised: 11/30/2017] [Accepted: 12/02/2017] [Indexed: 01/09/2023]
Abstract
Knowledge of protein stability is of utmost importance in various fields of biotechnology. Protein stability can be assessed in solution by increasing the concentration of denaturant and recording the structural changes with spectroscopic or thermodynamic methods. The standard interpretation of the experimental data is to assume a 2-state equilibrium between completely folded and completely unfolded protein molecules. Here we propose a cooperative model based on the statistical-mechanical Zimm-Bragg theory. In this model protein unfolding is driven by the weak binding of a rather small number of denaturant molecules, inducing the cooperative unfolding with multiple dynamic intermediates. The modified Zimm-Bragg theory is applied to published thermodynamic and spectroscopic data leading to the following conclusions. (i) The binding constant KD is correlated with the midpoint concentration, c0, of the unfolding reaction according to c0≅1/KD. The better the binding of denaturant the lower is the concentration to achieve unfolding. (ii) The binding constant KD agrees with direct thermodynamic measurements. A rather small number of bound denaturants suffices to induce the cooperative unfolding of the whole protein. (iii) Chemical unfolding occurs in the concentration range ΔcD=cend-cini. The theory predicts the unfolding energy per amino acid residue as gnu=RTKD(cend-cini). The Gibbs free energy of an osmotic gradient of the same size is ΔGDiff=-RTln(cend/cini). In all examples investigated ΔGDiff exactly balances the unfolding energy gnu. The total unfolding energy is thus close to zero. (iv) Protein cooperativity in chemical unfolding is rather low with cooperativity parameters σ≥3x10-3. As a consequence, the theory predicts a dynamic mixture of conformations during the unfolding reaction. The probabilities of individual conformations are easily accessible via the partition function Z(cD,σ).
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Affiliation(s)
- J Seelig
- Biozentrum, University of Basel, Klingelbergstrasse 70, CH-4056 Basel, Switzerland.
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13
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El-Baba TJ, Kim D, Rogers DB, Khan FA, Hales DA, Russell DH, Clemmer DE. Long-Lived Intermediates in a Cooperative Two-State Folding Transition. J Phys Chem B 2016; 120:12040-12046. [PMID: 27933943 DOI: 10.1021/acs.jpcb.6b08932] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022]
Abstract
Biomolecular folding often occurs through a cooperative two-state reactant ↔ product transition; the term cooperative does not convey that intermediate structures are nonexistent but rather that these states are not observable by existing experimental techniques. Because of this, few intermediates have been studied and characterized. Recently, ion mobility spectrometry (IMS) measurements revealed that the oligomer polyproline-13 (Pro13, which in propanol (PrOH) favors the right-handed helical PPI structure having adjacent pyrrolidine rings in a cis configuration) folds through six sequential long-lived intermediates as it converts to the all-trans-configured PPII structure that is favored in aqueous solutions. Here, we examine the PPIPrOH → PPIIaq folding transition for a HisPro13 sequence, i.e., Pro13 having a single histidine residue added to the N-terminus. Remarkably, the IMS measurements show that, upon addition of histidine, all of the IMS peaks associated with intermediate structures disappear. Instead, HisPro13 folds via a cooperative two-state transition, delayed by a significant induction period. The induction period is temperature dependent-shifting the transition to longer times at lower temperatures. Equilibrium studies show that the HisPro13 PPIPrOH → PPIIaq transition is endothermic but favored entropically. From these clues, we propose a sequential folding mechanism and develop a model that suggests that ∼13-17 long-lived intermediates are likely responsible for the induction period. In this model, intermediates are separated by average individual activation barriers of ∼90 kJ·mol-1, and are entropically favorable.
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Affiliation(s)
- Tarick J El-Baba
- Department of Chemistry, Indiana University , 800 Kirkwood Avenue, Bloomington, Indiana 47401, United States
| | - Doyong Kim
- Department of Chemistry, Texas A&M University , College Station, Texas 77843, United States
| | - Dylan B Rogers
- Department of Chemistry, Hendrix College , Conway, Arkansas 72032, United States
| | - Faizan A Khan
- Department of Chemistry, Hendrix College , Conway, Arkansas 72032, United States
| | - David A Hales
- Department of Chemistry, Hendrix College , Conway, Arkansas 72032, United States
| | - David H Russell
- Department of Chemistry, Texas A&M University , College Station, Texas 77843, United States
| | - David E Clemmer
- Department of Chemistry, Indiana University , 800 Kirkwood Avenue, Bloomington, Indiana 47401, United States
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14
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Pang YP. FF12MC: A revised AMBER forcefield and new protein simulation protocol. Proteins 2016; 84:1490-516. [PMID: 27348292 PMCID: PMC5129589 DOI: 10.1002/prot.25094] [Citation(s) in RCA: 27] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/11/2016] [Revised: 06/16/2016] [Accepted: 06/18/2016] [Indexed: 12/25/2022]
Abstract
Specialized to simulate proteins in molecular dynamics (MD) simulations with explicit solvation, FF12MC is a combination of a new protein simulation protocol employing uniformly reduced atomic masses by tenfold and a revised AMBER forcefield FF99 with (i) shortened CH bonds, (ii) removal of torsions involving a nonperipheral sp(3) atom, and (iii) reduced 1-4 interaction scaling factors of torsions ϕ and ψ. This article reports that in multiple, distinct, independent, unrestricted, unbiased, isobaric-isothermal, and classical MD simulations FF12MC can (i) simulate the experimentally observed flipping between left- and right-handed configurations for C14-C38 of BPTI in solution, (ii) autonomously fold chignolin, CLN025, and Trp-cage with folding times that agree with the experimental values, (iii) simulate subsequent unfolding and refolding of these miniproteins, and (iv) achieve a robust Z score of 1.33 for refining protein models TMR01, TMR04, and TMR07. By comparison, the latest general-purpose AMBER forcefield FF14SB locks the C14-C38 bond to the right-handed configuration in solution under the same protein simulation conditions. Statistical survival analysis shows that FF12MC folds chignolin and CLN025 in isobaric-isothermal MD simulations 2-4 times faster than FF14SB under the same protein simulation conditions. These results suggest that FF12MC may be used for protein simulations to study kinetics and thermodynamics of miniprotein folding as well as protein structure and dynamics. Proteins 2016; 84:1490-1516. © 2016 The Authors Proteins: Structure, Function, and Bioinformatics Published by Wiley Periodicals, Inc.
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Affiliation(s)
- Yuan-Ping Pang
- Computer-Aided Molecular Design Laboratory, Mayo Clinic, Rochester, MN, 55905, USA.
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15
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Lang SE, Stevenson TK, Xu D, O'Connell R, Westfall MV. Functionally conservative substitutions at cardiac troponin I S43/45. Arch Biochem Biophys 2016; 601:42-7. [PMID: 26869200 PMCID: PMC4899172 DOI: 10.1016/j.abb.2016.02.002] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/18/2015] [Revised: 01/13/2016] [Accepted: 02/01/2016] [Indexed: 12/22/2022]
Abstract
A phospho-null Ala substitution at protein kinase C (PKC)-targeted cardiac troponin I (cTnI) S43/45 reduces myocyte and cardiac contractile function. The goal of the current study was to test whether cTnIS43/45N is an alternative, functionally conservative substitution in cardiac myocytes. Partial and more extensive endogenous cTnI replacement was similar at 2 and 4 days after gene transfer, respectively, for epitope-tagged cTnI and cTnIS43/45N. This replacement did not significantly change thin filament stoichiometry. In functional studies, there were no significant changes in the amplitude and/or rates of contractile shortening and re-lengthening after this partial (2 days) and extensive (4 days) replacement with cTnIS43/45N. The cTnIS43/45N substitution also was not associated with adaptive changes in the myocyte Ca(2+) transient or in phosphorylation of the protein kinase A and C-targeted cTnIS23/24 site. These results provide evidence that cTnIS43/45N is a functionally conservative substitution, and may be appropriate for use as a phospho-null in rodent models designed for studies on PKC modulation of cardiac performance.
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Affiliation(s)
- Sarah E Lang
- Program in Cellular and Molecular Biology, University of Michigan, Ann Arbor, MI 48109, USA
| | - Tamara K Stevenson
- Department of Cardiac Surgery, University of Michigan, Ann Arbor, MI 48109, USA; Department of Molecular and Integrative Physiology, University of Michigan, Ann Arbor, MI 48109, USA
| | - Dongyang Xu
- Department of Biomedical Engineering, University of Michigan, Ann Arbor, MI 48109, USA
| | - Ryan O'Connell
- Department of Molecular and Integrative Physiology, University of Michigan, Ann Arbor, MI 48109, USA
| | - Margaret V Westfall
- Program in Cellular and Molecular Biology, University of Michigan, Ann Arbor, MI 48109, USA; Department of Cardiac Surgery, University of Michigan, Ann Arbor, MI 48109, USA; Department of Molecular and Integrative Physiology, University of Michigan, Ann Arbor, MI 48109, USA; Department of Biomedical Engineering, University of Michigan, Ann Arbor, MI 48109, USA.
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16
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Thermal protein unfolding by differential scanning calorimetry and circular dichroism spectroscopy Two-state model versus sequential unfolding. Q Rev Biophys 2016; 49:e9. [PMID: 27658613 DOI: 10.1017/s0033583516000044] [Citation(s) in RCA: 41] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/05/2022]
Abstract
Thermally-induced protein unfolding is commonly described with the two-state model. This model assumes only two types of protein molecules in solution, the native (N) and the denatured, unfolded (U) protein. In reality, protein unfolding is a multistep process, even if intermediate states are only sparsely populated. As an alternative approach we explore the Zimm-Bragg theory, originally developed for the α-helix-to-random coil transition of synthetic polypeptides. The theory includes intermediate structures with concentrations determined by the cooperativity of the unfolding reaction. We illustrate the differences between the two-state model and the Zimm-Bragg theory with measurements of apolipoprotein A-1 and lysozyme by differential scanning calorimetry (DSC) and CD spectroscopy. Nine further protein examples are taken from the literature. The Zimm-Bragg theory provides a perfect fit of the calorimetric unfolding transitions for all proteins investigated. In contrast, the transition curves and enthalpies predicted by the two-state model differ considerably from the experimental results. Apolipoprotein A-1 is ~50% α-helical at ambient temperature and its unfolding follows the classical α-helix-to-random coil equilibrium. The unfolding of proteins with little α-helix content, such as lysozyme, can also be analyzed with the Zimm-Bragg theory by introducing the concept of 'folded' and 'unfolded' peptide units assuming an average unfolding enthalpy per peptide unit. DSC is the method of choice to measure the unfolding enthalpy, , but CD spectroscopy in combination with the two-state model is often used to deduce the unfolding enthalpy. This can lead to erroneous result. Not only are different enthalpies required to describe the CD and DSC transition curves but these values deviate distinctly from the experimental result. In contrast, the Zimm-Bragg theory predicts the DSC and CD unfolding transitions with the same set of parameters.
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17
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Cromm PM, Spiegel J, Grossmann TN. Hydrocarbon stapled peptides as modulators of biological function. ACS Chem Biol 2015; 10:1362-75. [PMID: 25798993 DOI: 10.1021/cb501020r] [Citation(s) in RCA: 220] [Impact Index Per Article: 24.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022]
Abstract
Peptide-based drug discovery has experienced a significant upturn within the past decade since the introduction of chemical modifications and unnatural amino acids has allowed for overcoming some of the drawbacks associated with peptide therapeutics. Strengthened by such features, modified peptides become capable of occupying a niche that emerges between the two major classes of today's therapeutics-small molecules (<500 Da) and biologics (>5000 Da). Stabilized α-helices have proven particularly successful at impairing disease-relevant PPIs previously considered "undruggable." Among those, hydrocarbon stapled α-helical peptides have emerged as a novel class of potential peptide therapeutics. This review provides a comprehensive overview of the development and applications of hydrocarbon stapled peptides discussing the benefits and limitations of this technique.
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Affiliation(s)
- Philipp M. Cromm
- Max Planck Institute of Molecular Physiology, Otto-Hahn-Str. 11, 44227 Dortmund, Germany
- Technical University Dortmund, Department of Chemistry and Chemical Biology, Otto-Hahn-Str. 6, 44227 Dortmund, Germany
| | - Jochen Spiegel
- Max Planck Institute of Molecular Physiology, Otto-Hahn-Str. 11, 44227 Dortmund, Germany
- Technical University Dortmund, Department of Chemistry and Chemical Biology, Otto-Hahn-Str. 6, 44227 Dortmund, Germany
| | - Tom N. Grossmann
- Max Planck Institute of Molecular Physiology, Otto-Hahn-Str. 11, 44227 Dortmund, Germany
- Technical University Dortmund, Department of Chemistry and Chemical Biology, Otto-Hahn-Str. 6, 44227 Dortmund, Germany
- Chemical Genomics Centre of the Max Planck Society, Otto-Hahn-Str. 15, 44227 Dortmund, Germany
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18
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19
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Kragelj J, Blackledge M, Jensen MR. Ensemble Calculation for Intrinsically Disordered Proteins Using NMR Parameters. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 2015; 870:123-47. [PMID: 26387101 DOI: 10.1007/978-3-319-20164-1_4] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/17/2022]
Abstract
Intrinsically disordered proteins (IDPs) perform their function despite their lack of well-defined tertiary structure. Residual structure has been observed in IDPs, commonly described as transient/dynamic or expressed in terms of fractional populations. In order to understand how the protein primary sequence dictates the dynamic and structural properties of IDPs and in general to understand how IDPs function, atomic-level descriptions are needed. Nuclear magnetic resonance spectroscopy provides information about local and long-range structure in IDPs at amino acid specific resolution and can be used in combination with ensemble descriptions to represent the dynamic nature of IDPs. In this chapter we describe sample-and-select approaches for ensemble modelling of local structural propensities in IDPs with specific emphasis on validation of these ensembles.
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Affiliation(s)
- Jaka Kragelj
- IBS, University Grenoble Alpes, 38044, Grenoble, France.,IBS, CNRS, 38044, Grenoble, France.,IBS, CEA, 38044, Grenoble, France
| | - Martin Blackledge
- IBS, University Grenoble Alpes, 38044, Grenoble, France.,IBS, CNRS, 38044, Grenoble, France.,IBS, CEA, 38044, Grenoble, France
| | - Malene Ringkjøbing Jensen
- IBS, University Grenoble Alpes, 38044, Grenoble, France. .,IBS, CNRS, 38044, Grenoble, France. .,IBS, CEA, 38044, Grenoble, France.
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20
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Bao D, Upadhyayula S, Larsen JM, Xia B, Georgieva B, Nuñez V, Espinoza EM, Hartman JD, Wurch M, Chang A, Lin CK, Larkin J, Vasquez K, Beran GJO, Vullev VI. Dipole-mediated rectification of intramolecular photoinduced charge separation and charge recombination. J Am Chem Soc 2014; 136:12966-73. [PMID: 25162490 DOI: 10.1021/ja505618n] [Citation(s) in RCA: 43] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
Abstract
Controlling charge transfer at a molecular scale is critical for efficient light harvesting, energy conversion, and nanoelectronics. Dipole-polarization electrets, the electrostatic analogue of magnets, provide a means for "steering" electron transduction via the local electric fields generated by their permanent electric dipoles. Here, we describe the first demonstration of the utility of anthranilamides, moieties with ordered dipoles, for controlling intramolecular charge transfer. Donor-acceptor dyads, each containing a single anthranilamide moiety, distinctly rectify both the forward photoinduced electron transfer and the subsequent charge recombination. Changes in the observed charge-transfer kinetics as a function of media polarity were consistent with the anticipated effects of the anthranilamide molecular dipoles on the rectification. The regioselectivity of electron transfer and the molecular dynamics of the dyads further modulated the observed kinetics, particularly for charge recombination. These findings reveal the underlying complexity of dipole-induced effects on electron transfer and demonstrate unexplored paradigms for molecular rectifiers.
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Affiliation(s)
- Duoduo Bao
- Department of Bioengineering, ‡Department of Biochemistry, §Department of Chemistry, and ∥Materials Science and Engineering Program, University of California , Riverside, California 92521, United States
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21
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Boehm CR, Terentjev EM. Minimal Model of Intrinsic Chirality to Study the Folding Behavior of Helical Polymers. Macromolecules 2014. [DOI: 10.1021/ma500720t] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Affiliation(s)
- Christian R. Boehm
- Cavendish Laboratory, University of Cambridge, JJ Thomson Avenue, Cambridge CB3 0HE, U.K
| | - Eugene M. Terentjev
- Cavendish Laboratory, University of Cambridge, JJ Thomson Avenue, Cambridge CB3 0HE, U.K
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22
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Sharma GVM, Ravindranath H, Bhaskar A, Jeelani Basha S, Gurava Reddy PRG, Sirisha K, Sarma AVS, Hofmann HJ. Design and Study of Peptides Containing 1:1 Left- and Right-Handed Helical Patterns from Aminopyrancarboxylic Acids. European J Org Chem 2014. [DOI: 10.1002/ejoc.201402123] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022]
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23
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Tsuji M. Local motifs involved in the canonical structure of the ligand-binding domain in the nuclear receptor superfamily. J Struct Biol 2013; 185:355-65. [PMID: 24361687 DOI: 10.1016/j.jsb.2013.12.007] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/02/2013] [Revised: 12/14/2013] [Accepted: 12/16/2013] [Indexed: 11/19/2022]
Abstract
Structural and sequence alignment analyses have revealed the existence of class-dependent and -independent local motifs involved in the overall fold of the ligand-binding domain (LBD) in the nuclear receptor (NR) superfamily. Of these local motifs, three local motifs, i.e., AF-2 fixed motifs, were involved in the agonist conformation of the activation function-2 (AF-2) region of the LBD. Receptor-agonist interactions increased the stability of these AF-2 fixed motifs in the agonist conformation. In contrast, perturbation of the AF-2 fixed motifs by a ligand or another protein molecule led the AF-2 architecture to adopt an antagonist conformation. Knowledge of this process should provide us with novel insights into the 'agonism' and 'antagonism' of NRs.
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Affiliation(s)
- Motonori Tsuji
- Institute of Molecular Function, 2-105-14 Takasu, Misato-shi, Saitama 341-0037, Japan.
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24
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Gevorkian SG, Allahverdyan AE, Gevorgyan DS, Simonian AL, Hu CK. Stabilization and anomalous hydration of collagen fibril under heating. PLoS One 2013; 8:e78526. [PMID: 24244320 PMCID: PMC3823754 DOI: 10.1371/journal.pone.0078526] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/22/2013] [Accepted: 09/20/2013] [Indexed: 11/19/2022] Open
Abstract
BACKGROUND Type I collagen is the most common protein among higher vertebrates. It forms the basis of fibrous connective tissues (tendon, chord, skin, bones) and ensures mechanical stability and strength of these tissues. It is known, however, that separate triple-helical collagen macromolecules are unstable at physiological temperatures. We want to understand the mechanism of collagen stability at the intermolecular level. To this end, we study the collagen fibril, an intermediate level in the collagen hierarchy between triple-helical macromolecule and tendon. METHODOLOGY/PRINCIPAL FINDING When heating a native fibril sample, its Young's modulus decreases in temperature range 20-58°C due to partial denaturation of triple-helices, but it is approximately constant at 58-75°C, because of stabilization by inter-molecular interactions. The stabilization temperature range 58-75°C has two further important features: here the fibril absorbs water under heating and the internal friction displays a peak. We relate these experimental findings to restructuring of collagen triple-helices in fibril. A theoretical description of the experimental results is provided via a generalization of the standard Zimm-Bragg model for the helix-coil transition. It takes into account intermolecular interactions of collagen triple-helices in fibril and describes water adsorption via the Langmuir mechanism. CONCLUSION/SIGNIFICANCE We uncovered an inter-molecular mechanism that stabilizes the fibril made of unstable collagen macromolecules. This mechanism can be relevant for explaining stability of collagen.
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Affiliation(s)
- Sasun G. Gevorkian
- Institute of Physics, Academia Sinica, Taipei, Taiwan
- Yerevan Physics Institute, Yerevan, Armenia
| | | | - David S. Gevorgyan
- Institute of Fine Organic Chemistry, Scientific-Technological Center of Organic and Pharmaceutical Chemistry, Yerevan, Armenia
| | - Aleksandr L. Simonian
- Materials Research and Education Center, Auburn University, Auburn, Alabama, United States of America
| | - Chin-Kun Hu
- Institute of Physics, Academia Sinica, Taipei, Taiwan
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25
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Francis BR. Evolution of the genetic code by incorporation of amino acids that improved or changed protein function. J Mol Evol 2013; 77:134-58. [PMID: 23743924 DOI: 10.1007/s00239-013-9567-y] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/11/2013] [Accepted: 05/25/2013] [Indexed: 12/31/2022]
Abstract
Fifty years have passed since the genetic code was deciphered, but how the genetic code came into being has not been satisfactorily addressed. It is now widely accepted that the earliest genetic code did not encode all 20 amino acids found in the universal genetic code as some amino acids have complex biosynthetic pathways and likely were not available from the environment. Therefore, the genetic code evolved as pathways for synthesis of new amino acids became available. One hypothesis proposes that early in the evolution of the genetic code four amino acids-valine, alanine, aspartic acid, and glycine-were coded by GNC codons (N = any base) with the remaining codons being nonsense codons. The other sixteen amino acids were subsequently added to the genetic code by changing nonsense codons into sense codons for these amino acids. Improvement in protein function is presumed to be the driving force behind the evolution of the code, but how improved function was achieved by adding amino acids has not been examined. Based on an analysis of amino acid function in proteins, an evolutionary mechanism for expansion of the genetic code is described in which individual coded amino acids were replaced by new amino acids that used nonsense codons differing by one base change from the sense codons previously used. The improved or altered protein function afforded by the changes in amino acid function provided the selective advantage underlying the expansion of the genetic code. Analysis of amino acid properties and functions explains why amino acids are found in their respective positions in the genetic code.
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Affiliation(s)
- Brian R Francis
- Department of Molecular Biology, University of Wyoming, Laramie, WY, 82071-3944, USA,
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26
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Ali AM, Woolley GA. The effect of azobenzene cross-linker position on the degree of helical peptide photo-control. Org Biomol Chem 2013; 11:5325-31. [DOI: 10.1039/c3ob40684a] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
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27
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Chemmama IE, Pelea AC, Bhandari YR, Chapagain PP, Gerstman BS. Structural propensities and entropy effects in peptide helix-coil transitions. PHYSICAL REVIEW. E, STATISTICAL, NONLINEAR, AND SOFT MATTER PHYSICS 2012; 86:031915. [PMID: 23030952 DOI: 10.1103/physreve.86.031915] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/05/2012] [Revised: 07/13/2012] [Indexed: 06/01/2023]
Abstract
The helix-coil transition in peptides is a critical structural transition leading to functioning proteins. Peptide chains have a large number of possible configurations that must be accounted for in statistical mechanical investigations. Using hydrogen bond and local helix propensity interaction terms, we develop a method for obtaining and incorporating the degeneracy factor that allows the exact calculation of the partition function for a peptide as a function of chain length. The partition function is used in calculations for engineered peptide chains of various lengths that allow comparison with a variety of different types of experimentally measured quantities, such as fraction of helicity as a function of both temperature and chain length, heat capacity, and denaturation studies. When experimental sensitivity in helicity measurements is properly accounted for in the calculations, the calculated curves fit well with the experimental curves. We determine values of interaction energies for comparison with known biochemical interactions, as well as quantify the difference in the number of configurations available to an amino acid in a random coil configuration compared to a helical configuration.
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Affiliation(s)
- Ilan E Chemmama
- Department of Physics, Florida International University, University Park, Miami, Florida 33199, USA
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28
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Brandenburg E, von Berlepsch H, Gerling UIM, Böttcher C, Koksch B. Inhibition of amyloid aggregation by formation of helical assemblies. Chemistry 2012; 17:10651-61. [PMID: 22003512 DOI: 10.1002/chem.201100670] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
Abstract
The formation of amyloid aggregates is responsible for a wide range of diseases, including Alzheimer's and Parkinson's disease. Although the amyloid-forming proteins have different structures and sequences, all undergo a conformational change to form amyloid aggregates that have a characteristic cross-β-structure. The mechanistic details of this process are poorly understood, but different strategies for the development of inhibitors of amyloid formation have been proposed. In most cases, chemically diverse compounds bind to an elongated form of the protein in a β-strand conformation and thereby exert their therapeutic effect. However, this approach could favor the formation of prefibrillar oligomeric species, which are thought to be toxic. Herein, we report an alternative approach in which a helical coiled-coil-based inhibitor peptide has been designed to engage a coiled-coil-based amyloid-forming model peptide in a stable coiled-coil arrangement, thereby preventing rearrangement into a β-sheet conformation and the subsequent formation of amyloid-like fibrils. Moreover, we show that the helix-forming peptide is able to disassemble mature amyloid-like fibrils.
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29
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Itoh T, Hatanaka T, Ihara E, Inoue K. Helix–coil transformation of poly(γ-benzyl-L-glutamate) with polystyrene attached to the N or C terminus in trifluoroacetic acid–chloroform mixtures. Polym J 2011. [DOI: 10.1038/pj.2011.113] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
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30
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Altamore TM, Fernández-García C, Gordon AH, Hübscher T, Promsawan N, Ryadnov MG, Doig AJ, Woolfson DN, Gallagher T. Random-Coil:α-Helix Equilibria as a Reporter for the LewisX-LewisX Interaction. Angew Chem Int Ed Engl 2011; 50:11167-71. [DOI: 10.1002/anie.201101055] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/11/2011] [Revised: 04/19/2011] [Indexed: 12/29/2022]
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31
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Altamore TM, Fernández-García C, Gordon AH, Hübscher T, Promsawan N, Ryadnov MG, Doig AJ, Woolfson DN, Gallagher T. Random-Coil:α-Helix Equilibria as a Reporter for the LewisX-LewisX Interaction. Angew Chem Int Ed Engl 2011. [DOI: 10.1002/ange.201101055] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022]
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32
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Upadhyayula S, Bao D, Millare B, Sylvia SS, Habib KMM, Ashraf K, Ferreira A, Bishop S, Bonderer R, Baqai S, Jing X, Penchev M, Ozkan M, Ozkan CS, Lake RK, Vullev VI. Permanent electric dipole moments of carboxyamides in condensed media: what are the limitations of theory and experiment? J Phys Chem B 2011; 115:9473-90. [PMID: 21682315 DOI: 10.1021/jp2045383] [Citation(s) in RCA: 35] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/09/2023]
Abstract
Electrostatic properties of proteins are crucial for their functionality. Carboxyamides are small polar groups that, as peptide bonds, are principal structural components of proteins that govern their electrostatic properties. We investigated the medium dependence of the molar polarization and of the permanent dipole moments of amides with different state of alkylation. The experimentally measured and theoretically calculated dipole moments manifested a solvent dependence that increased with the increase in the media polarity. We ascribed the observed enhancement of the amide polarization to the reaction fields in the solvated cavities. Chloroform, for example, caused about a 25% increase in the amide dipole moments determined for vacuum, as the experimental and theoretical results demonstrated. Another chlorinated solvent, 1,1,2,2-tetrachloroethane, however, caused an "abnormal" increase in the experimentally measured amide dipoles, which the theoretical approaches we used could not readily quantify. We showed and discussed alternatives for addressing such discrepancies between theory and experiment.
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Affiliation(s)
- Srigokul Upadhyayula
- Department of Bioengineering, University of California, Riverside, California 92521, United States
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33
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The contribution of entropy, enthalpy, and hydrophobic desolvation to cooperativity in repeat-protein folding. Structure 2011; 19:349-60. [PMID: 21397186 DOI: 10.1016/j.str.2010.12.018] [Citation(s) in RCA: 60] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/06/2010] [Revised: 11/23/2010] [Accepted: 12/10/2010] [Indexed: 11/22/2022]
Abstract
Cooperativity is a defining feature of protein folding, but its thermodynamic and structural origins are not completely understood. By constructing consensus ankyrin repeat protein arrays that have nearly identical sequences, we quantify cooperativity by resolving stability into intrinsic and interfacial components. Heteronuclear NMR and CD spectroscopy show that these constructs adopt ankyrin repeat structures. Applying a one-dimensional Ising model to a series of constructs chosen to maximize information content in unfolding transitions, we quantify stabilities of the terminal capping repeats, and resolve the effects of denaturant into intrinsic and interfacial components. Reversible thermal denaturation resolves interfacial and intrinsic free energies into enthalpic, entropic, and heat capacity terms. Intrinsic folding is entropically disfavored, whereas interfacial interaction is entropically favored and attends a decrease in heat capacity. These results suggest that helix formation and backbone ordering occurs upon intrinsic folding, whereas hydrophobic desolvation occurs upon interfacial interaction, contributing to cooperativity.
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Abstract
The nucleation event in α-helix formation is a fundamental process in protein folding. However, determining how quickly it takes place based on measurements of the relaxation dynamics of helical peptides is difficult because such relaxations invariably contain contributions from various structural transitions such as from helical to nonhelical states and helical to partial-helical conformations. Herein, we measure the temperature-jump (T-jump) relaxation kinetics of three model peptides that fold into a single-turn α-helix, using time-resolved infrared spectroscopy, aiming to provide a direct assessment of the helix nucleation rate. The α-helical structure of these peptides is stabilized by a covalent cross-linker formed between the side chains of two residues at the i and i + 4 positions. If we assume that this cross-linker mimics the structural constraint arising from a strong side chain-side chain interaction (e.g., a salt bridge) in proteins, these peptides would represent good models for studying the nucleation process of an α-helix in a protein environment. Indeed, we find that the T-jump induced relaxation rate of these peptides is approximately (0.6 μs)(-1) at room temperature, which is slower than that of commonly studied alanine-based helical peptides but faster than that of a naturally occurring α-helix whose folded state is stabilized by a series of side chain-side chain interactions. Taken together, our results put an upper limit of about 1 μs for the helix nucleation time at 20 °C and suggest that the subsequent propagation steps occur with a time constant of about 240 ns.
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Affiliation(s)
| | | | - Feng Gai
- Department of Chemistry, University of Pennsylvania, Philadelphia, PA 19104
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35
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Wrabl JO, Gu J, Liu T, Schrank TP, Whitten ST, Hilser VJ. The role of protein conformational fluctuations in allostery, function, and evolution. Biophys Chem 2011; 159:129-41. [PMID: 21684672 DOI: 10.1016/j.bpc.2011.05.020] [Citation(s) in RCA: 90] [Impact Index Per Article: 6.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/31/2011] [Revised: 05/26/2011] [Accepted: 05/26/2011] [Indexed: 11/17/2022]
Abstract
It is now well-known that proteins exist at equilibrium as ensembles of conformational states rather than as unique static structures. Here we review from an ensemble perspective important biological effects of such spontaneous fluctuations on protein allostery, function, and evolution. However, rather than present a thorough literature review on each subject, we focus instead on connecting these phenomena through the ensemble-based experimental, theoretical, and computational investigations from our laboratory over the past decade. Special emphasis is given to insights that run counter to some of the prevailing ideas that have emerged over the past 40 years of structural biology research. For instance, when proteins are viewed as conformational ensembles rather than as single structures, the commonly held notion of an allosteric pathway as an obligate series of individual structural distortions loses its meaning. Instead, allostery can result from energetic linkage between distal sites as one Boltzmann distribution of states transitions to another. Additionally, the emerging principles from this ensemble view of proteins have proven surprisingly useful in describing the role of intrinsic disorder in inter-domain communication, functional adaptation mediated by mutational control of fluctuations, and evolutionary conservation of the energetics of protein stability.
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Affiliation(s)
- James O Wrabl
- Departments of Biology and Biophysics, Johns Hopkins University, Baltimore, MD 21218, USA.
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36
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Lee TK, Ahn JM. Solid-phase synthesis of tris-benzamides as α-helix mimetics. ACS COMBINATORIAL SCIENCE 2011; 13:107-11. [PMID: 21395339 DOI: 10.1021/co100056c] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Small molecules mimicking α-helices are of great interest since numerous protein-protein interactions use helical structures at the interface. With a goal of generating libraries of α-helix mimetics, an efficient solid-phase synthetic method was developed to produce tris-benzamides. The tris-benzamide scaffold was designed to place three side-chain functional groups found at the i, i + 4, and i + 7 positions of an α-helix, emulating one helical face. The synthetic strategy involves simple and iterative reactions of removal of an allyl ester, formation of an amide bond via an O → N acyl migration, and an O-alkylation. A small library of twenty tris-benzamides containing a variety of functional groups was prepared in high purity (83-99%) to demonstrate the versatility of the synthetic approach. This methodology allowed the facile and rapid construction of α-helix mimetics that would facilitate the identification of small molecules for target proteins.
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Affiliation(s)
- Tae-Kyung Lee
- Department of Chemistry, University of Texas at Dallas, Richardson, Texas 75080, United States
| | - Jung-Mo Ahn
- Department of Chemistry, University of Texas at Dallas, Richardson, Texas 75080, United States
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Kanô F, Shinjo M, Qin ZJ, Li J, Matsumura Y, Shimizu A, Teramoto A, Kihara H. Denaturant-induced helix–coil transition of oligopeptides: theoretical and equilibrium studies of short oligopeptides C17 and AK16. Polym J 2011. [DOI: 10.1038/pj.2010.143] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
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Top A, Kiick KL. Multivalent protein polymers with controlled chemical and physical properties. Adv Drug Deliv Rev 2010; 62:1530-40. [PMID: 20562016 PMCID: PMC3025749 DOI: 10.1016/j.addr.2010.05.002] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/23/2009] [Revised: 05/04/2010] [Accepted: 05/07/2010] [Indexed: 10/19/2022]
Abstract
In this review, we describe our work on the design, characterization, and modification of a series of alanine-rich helical polypeptides with novel functions. Glycosylation of the polypeptides has permitted investigation of polymer architecture effects on multivalent interactions. One of the members of this polypeptide family exhibits polymorphological behavior that is easily manipulated via simple changes in solution pH and temperature. Polypeptide-based fibrils formed at acidic pH and high temperature were shown to direct the one-dimensional organization of gold nanoparticles via electrostatic interactions. As a precursor to fibrils, aggregates likely comprising alanine-rich cores form at low temperatures and acidic pH and reversibly dissociate into monomers upon deprotonation. PEGylation of these polypeptides does not alter the self-association or conformational behavior of the polypeptide, suggesting potential applications in the development of assembled delivery vehicles, as modification of the polypeptides should be a useful strategy for controlling assembly.
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Affiliation(s)
- Ayben Top
- Department of Materials Science and Engineering, 201 DuPont Hall, University of Delaware, Newark, Delaware 19716
| | - Kristi L. Kiick
- Department of Materials Science and Engineering, 201 DuPont Hall, University of Delaware, Newark, Delaware 19716
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Two intracellular helices of G-protein coupling receptors could generally support oligomerization and coupling with transducers. Amino Acids 2010; 40:261-8. [PMID: 20571842 DOI: 10.1007/s00726-010-0616-1] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/21/2010] [Accepted: 04/27/2010] [Indexed: 10/19/2022]
Abstract
For many G-protein coupling receptors (GPCRs), the upkeep of receptor dimers could depend on association with functional Gi α subunits. This is known for Y1, Y2 and Y4 neuropeptide Y receptors [presented in the companion paper (Estes et al., Amino Acids, doi: 10.1007/s00726-010-0642-z , 2010)]. Interactions with transducers use mainly intracellular domains of the receptors. Intracellular loops 1 and 2 in GPCRs are short and lack extensive helicity that could support transducer anchoring. Interaction with G-proteins is known to use the juxtamembrane Helix 8 in the fourth intracellular domain, for which we document a helix-stabilizing n/(n + 4) pattern of large hydrophobic sidechains. Another intracellular helix located in the C-terminal portion of the third intracellular loop does not display a strong stabilizing pattern, and is found in many studies to serve dynamically in association and activation of transducers and effectors. We show that these tracts share features across metazoan phyla not only in opsins and opsin-like receptors (including the Y receptors), but also in Taste-2 and Frizzled receptors. Similarities of these helices across GPCR groups could have both phylogenetic and functional roots.
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40
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Schreck JS, Yuan JM. Exactly solvable model for helix-coil-sheet transitions in protein systems. PHYSICAL REVIEW. E, STATISTICAL, NONLINEAR, AND SOFT MATTER PHYSICS 2010; 81:061919. [PMID: 20866452 DOI: 10.1103/physreve.81.061919] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/27/2010] [Revised: 04/29/2010] [Indexed: 05/29/2023]
Abstract
In view of the important role helix-sheet transitions play in protein aggregation, we introduce a simple model to study secondary structural transitions of helix-coil-sheet systems using a Potts model starting with an effective Hamiltonian. This energy function depends on four parameters that approximately describe entropic and enthalpic contributions to the stability of a polypeptide in helical and sheet conformations. The sheet structures involve long-range interactions between residues which are far in sequence, but are in contact in real space. Such contacts are included in the Hamiltonian. Using standard statistical mechanical techniques, the partition function is solved exactly using transfer matrices. Based on this model, we study thermodynamic properties of polypeptides, including phase transitions between helix, sheet, and coil structures.
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Affiliation(s)
- John S Schreck
- Department of Physics, Drexel University, Philadelphia, Pennsylvania 19104, USA.
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41
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Nasr KA, Schubert CR, Török M, Kennedy RJ, Kemp DS. Helix-coil energetics for helix formers and breakers reflect context and temperature: mutants of helically robust, guest-sensitive homopeptide hosts. Biopolymers 2010; 91:311-20. [PMID: 19117030 DOI: 10.1002/bip.21129] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
The natural amino acids are primarily helix breakers at the low assignment temperatures characteristic of many studies, but recent genomic analyses of thermophilic proteins suggest that at high temperatures, some breakers may become strong helix formers. Moreover, the breaker/former inventory has not been previously characterized at the physiologically relevant temperature of 37 degrees C. The versatility of 13C==O NMR chemical shifts as helicity reporters allows construction of two mutant peptide series, tailored to expand the range of temperature assignments for helical propensities and derived from the core hosts tL-Ala9XxxAla9-tL and tL-AlaNva4XxxNva4Ala9-tL, Nva=norvaline. For three limiting guests Xxx, the helix former Nva and the breakers Gly and Pro, we report wXxx[T] assignments at seven temperatures from 2 to 80 degrees C, validating our reasoning and paving the way for assignment of a definitive wXxx[T] data-base.
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Affiliation(s)
- Khaled A Nasr
- Department of Chemistry, Room 6-433, Massachusetts Institute of Technology, Cambridge, MA 02139, USA
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42
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Xiong K, Asher SA. Circular dichroism and UV resonance raman study of the impact of alcohols on the Gibbs free energy landscape of an alpha-helical peptide. Biochemistry 2010; 49:3336-42. [PMID: 20225890 DOI: 10.1021/bi100176a] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
We used CD and UV resonance Raman spectroscopy to study the impact of alcohols on the conformational equilibria and relative Gibbs free energy landscapes along the Ramachandran Psi-coordinate of a mainly poly-Ala peptide, AP with an AAAAA(AAARA)(3)A sequence. 2,2,2-Trifluoroethanol (TFE) most stabilizes the alpha-helix-like conformations, followed by ethanol, methanol, and pure water. The pi-bulge conformation is stabilized more than the alpha-helix, while the 3(10)-helix is destabilized due to the alcohol-increased hydrophobicity. Turns are also stabilized by alcohols. We also found that while TFE induces more alpha-helices, it favors multiple, shorter helix segments.
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Affiliation(s)
- Kan Xiong
- Department of Chemistry, University of Pittsburgh, Pittsburgh, Pennsylvania 15260, USA
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Wathen B, Jia Z. Residue patterning in helix interiorsThis paper is one of a selection of papers published in this special issue entitled “Canadian Society of Biochemistry, Molecular & Cellular Biology 52nd Annual Meeting — Protein Folding: Principles and Diseases” and has undergone the Journal's usual peer review process. Biochem Cell Biol 2010; 88:325-37. [DOI: 10.1139/o09-156] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022] Open
Abstract
The α-helix remains a focus of research because of its importance to protein folding and structure. Nevertheless, despite numerous empirical, computational, and theoretical studies, the fundamental structural properties governing their formation and stability are still unclear. We have examined the statistical occurrence of polar and apolar residue patterning in helical interiors in a large, non-redundant dataset, and compared these patterns with those found in other structural environments. While the familiar amphipathic distributions for both polar and apolar residues are evident, our analysis also finds significant differences between these distributions. Non-amphipathic signals can also be discerned within both distributions. Most interestingly, among various positional patterning, an analysis of immediate (i,i + 1) helical neighbours found: (i) clear neighbouring preferences, with high (low) occurrences of hydrophobics (hydrophilics) next to Gly, Pro, and short polar residues; (ii) high negative (positive) correlation between residue helical propensities and the degree of neighbouring hydrophobicity (hydrophilicity); and (iii) a preferred ordering among neighbours, implying an inherent helix directionality. Because (i,i + 1) helical pairs have limited side chain – side chain interactions, thermodynamic considerations cannot readily explain these observations, nor can evolutionary pressures that enhance tertiary interactions via amphipathicity, as this particular spacing does not segregate residues onto either the same or opposing helical faces. We suggest that the mechanism of helix formation may be partly responsible for these observations. In particular, the high negative correlation between residue helical propensities and neighbouring hydrophobicity suggests that hydrophobicity may play a more important role in helix formation than currently recognized.
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Affiliation(s)
- Brent Wathen
- Department of Biochemistry, Queen’s University, Kingston, ON K7L 3N6, Canada
| | - Zongchao Jia
- Department of Biochemistry, Queen’s University, Kingston, ON K7L 3N6, Canada
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44
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Chaudhry BR, Wilton-Ely JDET, Tabor AB, Caruana DJ. Effect of peptide orientation on electron transfer. Phys Chem Chem Phys 2010; 12:9996-8. [DOI: 10.1039/c0cp00226g] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023]
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45
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Moreau RJ, Schubert CR, Nasr KA, Török M, Miller JS, Kennedy RJ, Kemp DS. Context-independent, temperature-dependent helical propensities for amino acid residues. J Am Chem Soc 2009; 131:13107-16. [PMID: 19702302 PMCID: PMC2770013 DOI: 10.1021/ja904271k] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Assigned from data sets measured in water at 2, 25, and 60 degrees C containing (13)C=O NMR chemical shifts and [theta](222) ellipticities, helical propensities are reported for the 20 genetically coded amino acids, as well as for norvaline and norleucine. These have been introduced by chemical synthesis at central sites within length-optimized, spaced, solubilized Ala(19) hosts. The resulting polyalanine-derived, quantitative propensity sets express for each residue its temperature-dependent but context-independent tendency to forego a coil state and join a preexisting helical conformation. At 2 degrees C their rank ordering is: P << G < H < C, T, N < S < Y, F, W < V, D < K < Q < I < R, M < L < E < A; at 60 degrees C the rank becomes: H, P < G < C < R, K < T, Y, F < N, V < S < Q < W, D < I, M < E < A < L. The DeltaDeltaG values, kcal/mol, relative to alanine, for the cluster T, N, S, Y, F, W, V, D, Q, imply that at 2 degrees C all are strong breakers: DeltaDeltaG(mean) = +0.63 +/- 0.11, but at 60 degrees C their breaking tendencies are dramatically attenuated and converge toward the mean: DeltaDeltaG(mean) = +0.25 +/- 0.07. Accurate modeling of helix-rich proteins found in thermophiles, mesophiles, and organisms that flourish near 0 degrees C thus requires appropriately matched propensity sets. Comparisons are offered between the temperature-dependent propensity assignments of this study and those previously assigned by the Scheraga group; the special problems that attend propensity assignments for charged residues are illustrated by lysine guest data; and comparisons of errors in helicity assignments from shifts and ellipticity data show that the former provide superior precision and accuracy.
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Affiliation(s)
- Robert J Moreau
- Department of Chemistry, Room 6-433, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA
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Bannerman MN, Magee JE, Lue L. Structure and stability of helices in square-well homopolymers. PHYSICAL REVIEW. E, STATISTICAL, NONLINEAR, AND SOFT MATTER PHYSICS 2009; 80:021801. [PMID: 19792144 DOI: 10.1103/physreve.80.021801] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/21/2009] [Indexed: 05/28/2023]
Abstract
Recently, it has been demonstrated [Magee, Phys. Rev. Lett. 96, 207802 (2006)] that isolated square-well homopolymers can spontaneously break chiral symmetry and "freeze" into helical structures at sufficiently low temperatures. This behavior is interesting because the square-well homopolymer is itself achiral. In this work, we use event-driven molecular dynamics combined with an optimized parallel tempering scheme to study this polymer model over a wide range of parameters. We examine the conditions where the helix structure is stable and determine how the interaction parameters of the polymer govern the details of the helix structure. The width of the square well (proportional to lambda) is found to control the radius of the helix, which decreases with increasing well width until the polymer forms a coiled sphere for sufficiently large wells. The helices are found to be stable for only a "window" of molecular weights. If the polymer is too short, the helix will not form. If the polymer is too long, the helix is no longer the minimum energy structure, and other folded structures will form. The size of this window is governed by the chain stiffness, which in this model is a function of the ratio of the monomer size to the bond length. Outside this window, the polymer still freezes into a locked structure at low temperature; however, unless the chain is sufficiently stiff, this structure will not be unique and is similar to a glassy state.
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Affiliation(s)
- M N Bannerman
- School of Chemical Engineering and Analytical Science, The University of Manchester, Manchester M60 1QD, United Kingdom
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47
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Imamura H, Kato M. Effect of pressure on helix-coil transition of an alanine-based peptide: An FTIR study. Proteins 2009; 75:911-8. [DOI: 10.1002/prot.22302] [Citation(s) in RCA: 44] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
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48
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Folding by numbers: primary sequence statistics and their use in studying protein folding. Int J Mol Sci 2009; 10:1567-1589. [PMID: 19468326 PMCID: PMC2680634 DOI: 10.3390/ijms10041567] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/30/2009] [Revised: 03/30/2009] [Accepted: 04/02/2009] [Indexed: 11/16/2022] Open
Abstract
The exponential growth over the past several decades in the quantity of both primary sequence data available and the number of protein structures determined has provided a wealth of information describing the relationship between protein primary sequence and tertiary structure. This growing repository of data has served as a prime source for statistical analysis, where underlying relationships between patterns of amino acids and protein structure can be uncovered. Here, we survey the main statistical approaches that have been used for identifying patterns within protein sequences, and discuss sequence pattern research as it relates to both secondary and tertiary protein structure. Limitations to statistical analyses are discussed, and a context for their role within the field of protein folding is given. We conclude by describing a novel statistical study of residue patterning in β-strands, which finds that hydrophobic (i,i+2) pairing in β-strands occurs more often than expected at locations near strand termini. Interpretations involving β-sheet nucleation and growth are discussed.
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49
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Doig AJ. Statistical thermodynamics of the collagen triple-helix/coil transition. Free energies for amino acid substitutions within the triple-helix. J Phys Chem B 2009; 112:15029-33. [PMID: 18975885 DOI: 10.1021/jp805979k] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Collagen sequences frequently deviate from the most thermally stable (Gly-Pro-Hyp)(n) pattern, with many mutations causing osteogenesis imperfecta (or "brittle bone disease"). The effects of collagen mutations have been studied in short peptides. The analysis of this work is problematic, however, as triple-helices fray from their ends, making the coil/triple-helix equilibrium non-two-state. Here, I develop a statistical thermodynamic model to handle this equilibrium that is applicable to peptides that follow the (G-X-Y)(n) pattern, where Gly is present at every third position and where all three chains are identical. Parameters for substitutions at each position are included, as well as a penalty for initiating triple-helix formation. The model is applied to equilibrium experimental data at 37 degrees C to show that the extension of a triple-helix by a three residue unit stabilizes the triple-helix by 0.76 kcal/mol for Gly-Pro-Hyp and 0.33 kcal/mol for Gly-Pro-Pro. The replacement of Hyp by Arg, Asp, or Trp destabilizes the triple-helix by 1.5, 2.4, and 2.9 kcal/mol, respectively, where the substitution is present once in each chain. The model can thus be used to quantitatively interpret data on collagen peptides, giving free energies that can help rationalize mutations that affect collagen stability, and to design new collagen sequences.
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Affiliation(s)
- Andrew J Doig
- Manchester Interdisciplinary Biocentre, The University of Manchester, Manchester, UK.
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50
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Murza A, Kubelka J. Beyond the nearest-neighbor Zimm-Bragg model for helix-coil transition in peptides. Biopolymers 2009; 91:120-31. [PMID: 18814306 DOI: 10.1002/bip.21093] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
Affiliation(s)
- Adrian Murza
- Chemistry Department, University of Wyoming, Laramie, 82072, USA
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