Calorimetric Heat of the Helix-Coil Transition of Poly-L-glutamic Acid<sup>1a</sup>

Rialdi, G.; Hermans, Jan

doi:10.1021/ja00976a007

Cited by 74 publications

(53 citation statements)

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“…The estimated value of the heat is between -0.9 and -1.3 kcal/mole for forming helix from coil, depending on how the baseline is estimated. These numbers agree reasonably with values derived from helixcoil transition analysis of peptides with different chain length, as well as the precise titration and calorimetric analysis of the pH -dependent helix -coil transition in poly(Lys) and poly(Glu) (Hermans, 1966b;Rialdi and Hermans, 1966), -1.1 kcal/mole, suggesting that the favorable enthalpy responsible for driving helix formation is not highly sensitive to the side chain present. That is, the acid transition in poly(Glu), the alkaline transition in poly(Lys), and the neutral thermal transition in a long Ala-rich oligomer all yield enthalpy values near -1.1 ± 0.2 kcal/mole; the uncertainty still leaves some leeway for variation.…”

Section: Acykaaaakaaaakaaaak-amidesupporting

confidence: 84%

CD Spectroscopy and the Helix-Coil Transition in Peptides and Polypeptides

Kallenbach

Lyu

Zhou

1996

Circular Dichroism and the Conformational Analysis of Biomolecules

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Section: Acykaaaakaaaakaaaak-amidesupporting

confidence: 84%

CD Spectroscopy and the Helix-Coil Transition in Peptides and Polypeptides

Kallenbach

Lyu

Zhou

1996

Circular Dichroism and the Conformational Analysis of Biomolecules

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“…The enthalpies were calculated using the estimates for basis set superposition error (BSSE) taken from chains of five H-bonds (six formamides) frozen in the geometries assumed in each of the three H-bonding chains of the optimized helices in a manner somewhat similar to that described in an earlier report. 20 Both B3LYP and X3LYP predict results that are reasonably close to the several experimental values for polyalanine, [23][24][25] polyglutamic acid, 26 and polylysine, 27 and some previous predictive 28 theoretical values 20 available. While the experimental values refer to aqueous solution, we note that SM5.2 29 estimates of the differences in free energies of solvation for the α-helix and polyproline II structure of polyalanine are quite small.…”

Section: α-Helicessupporting

confidence: 66%

Comparison of some dispersion-corrected and traditional functionals as applied to peptides and conformations of cyclohexane derivatives

Marianski

Asensio

Dannenberg

2012

The Journal of Chemical Physics

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We compare the energetic and structural properties of fully optimized α-helical and antiparallel β-sheet polyalanines and the energetic differences between axial and equatorial conformations of three cyclohexane derivatives (methyl, fluoro, and chloro) as calculated using several functionals designed to treat dispersion (B97-D, ωB97x-D, M06, M06L, and M06-2X) with other traditional functionals not specifically parametrized to treat dispersion (B3LYP, X3LYP, and PBE1PBE) and with experimental results. Those functionals developed to treat dispersion significantly overestimate interaction enthalpies of folding for the α-helix and predict unreasonable structures that contain Ramachandran φ and ψ and C = O. . . N H-bonding angles that are out of the bounds of databases compiled the β-sheets. These structures are consistent with overestimation of the interaction energies. For the cyclohexanes, these functionals overestimate the stabilities of the axial conformation, especially when used with smaller basis sets. Their performance improves when the basis set is improved from D95** to aug-cc-pVTZ (which would not be possible with systems as large as the peptides).

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“…Although the calorimetric enthalpy measurement is direct, it is less precise than estimates of ⌬H obtained by using helix-coil theory to analyze thermal unfolding curves, because the unfolding curve even of a 50-residue peptide is very broad and fitting the baseline is problematic. Early estimates of the enthalpy of helix formation using homopolymers of poly-L-lysine and poly-L-glutamate gave values between Ϫ1.1 and Ϫ0.88 kcal͞mol residues (17,18). All these values are similar to each other and somewhat higher than a recent estimate of Ϫ0.65 kcal͞mol per residue by Taylor et al (19).…”

Section: Discussionmentioning

confidence: 50%

The enthalpy of the alanine peptide helix measured by isothermal titration calorimetry using metal-binding to induce helix formation

López

Chin

Baldwin

et al. 2002

Proc. Natl. Acad. Sci. U.S.A.

111

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The goal of this study is to use the model system described earlier to make direct measurements of the enthalpy of helix formation at different temperatures. For this we studied model alanine peptides in which helix formation can be triggered by metal (La 3؉ ) binding. The heat of La 3؉ interaction with the peptides at different temperatures is measured by isothermal titration calorimetry. Circular dichroism spectroscopy is used to follow helix formation. Peptides of increasing length (12-, 16-, and 19-aa residues) that contain a La 3؉ -binding loop followed by helices of increasing length, are used to separate the heat of metal binding from the enthalpy of helix formation. We demonstrate that (i) the enthalpy of helix formation is ؊0.9 ؎ 0.1 kcal͞mol; (ii) the enthalpy of helix formation is independent of the peptide length; (iii) the enthalpy of helix formation does not depend significantly on temperature in the range from 5 to 45°C, suggesting that the heat capacity change on helix formation is very small. Thus, the use of metal binding to induce helix formation has an enormous potential for measuring various thermodynamic properties of ␣-helices. The year 2001 marked the 50th anniversary of the ␣-helix, the first proposed protein secondary structure (1). However, despite numerous efforts (see refs. 2-5 and references therein), the detailed thermodynamic basis for helix formation and for the helix propensities of the amino acids is not yet well understood. Accurate values for such basic thermodynamic parameters as the changes in enthalpy and heat capacity on helix formation are still under debate. Recently Bierzynski and coworkers (6, 7) developed a peptide system for inducing helix formation by adding a metal ion. They took a 12-residue sequence, analogous to a Ca 2ϩ -binding loop from calmodulin (peptide P1), which forms a short and very stable C-terminal helix, containing three to four residues, when the peptide binds La 3ϩ . The C-terminal segment of La 3ϩ -bound P1 provides a stable helical nucleus for helix propagation when additional residues are added at the C terminus. Bierzynski and coworkers also made a longer peptide (P2) with three additional alanine residues plus one C-terminal glutamine residue, and determined the NMR structure of the La 3ϩ -ligated form. Their model system should allow accurate determination of the enthalpy of helix formation by using ITC (isothermal titration calorimetry) to monitor stepwise, La 3ϩ -induced helix formation, and we exploit this potential here.Helix-coil transitions of short peptides in water cannot usually be described by a two-state model because the helix propagation constant is not large enough. For this reason, and also because the enthalpy change on helix formation is not large, temperatureinduced helix unfolding spans a very broad temperature range, which makes it difficult to determine the baseline. Analysis of thermal helix-coil transitions can be based on the Zimm-Bragg or Lifson-Roig theories (e.g., see ref.2), but the enthalpy values determined in t...

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Calorimetric Heat of the Helix-Coil Transition of Poly-L-glutamic Acid^1a

Cited by 74 publications

References 0 publications

CD Spectroscopy and the Helix-Coil Transition in Peptides and Polypeptides

CD Spectroscopy and the Helix-Coil Transition in Peptides and Polypeptides

Comparison of some dispersion-corrected and traditional functionals as applied to peptides and conformations of cyclohexane derivatives

The enthalpy of the alanine peptide helix measured by isothermal titration calorimetry using metal-binding to induce helix formation

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Calorimetric Heat of the Helix-Coil Transition of Poly-L-glutamic Acid1a

Cited by 74 publications

References 0 publications

CD Spectroscopy and the Helix-Coil Transition in Peptides and Polypeptides

CD Spectroscopy and the Helix-Coil Transition in Peptides and Polypeptides

Comparison of some dispersion-corrected and traditional functionals as applied to peptides and conformations of cyclohexane derivatives

The enthalpy of the alanine peptide helix measured by isothermal titration calorimetry using metal-binding to induce helix formation

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Calorimetric Heat of the Helix-Coil Transition of Poly-L-glutamic Acid^1a