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Enthalpy of Helix-Coil Transition: Missing Link in Rationalizing the Thermodynamics of Helix-Forming Propensities of the Amino Acid Residues
It is known that different amino acid residues have effects on the thermodynamic stability of an α-helix. The underlying mechanism for the thermodynamic helical propensity is not well understood. The major accepted hypothesis is the difference in the side-chain configurational entropy loss upon heli...
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Published in: | Proceedings of the National Academy of Sciences - PNAS 2005-02, Vol.102 (5), p.1413-1418 |
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Main Authors: | , , , |
Format: | Article |
Language: | English |
Subjects: | |
Citations: | Items that this one cites Items that cite this one |
Online Access: | Get full text |
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Summary: | It is known that different amino acid residues have effects on the thermodynamic stability of an α-helix. The underlying mechanism for the thermodynamic helical propensity is not well understood. The major accepted hypothesis is the difference in the side-chain configurational entropy loss upon helix formation. However, the changes in the side-chain configurational entropy explain only part of the thermodynamic helical propensity, thus implying that there must be a difference in the enthalpy of helix-coil transition for different residues. This work provides an experimental test to this hypothesis. Direct calorimetric measurements of folding of a model host peptide in which the helix formation is induced by metal binding is applied to a wide range of residue types, both naturally occurring and nonnatural, at the guest site. Based on the calorimetric results for 12 peptides, it was found that indeed there is a difference in the enthalpy of helix-coil transition for different amino acid residues, and simple empirical rules that define these differences are presented. The obtained difference in the enthalpies of helix-coil transition complement the differences in configurational entropies and provide the complete thermodynamic characterization of the helix-forming tendencies. |
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ISSN: | 0027-8424 1091-6490 |
DOI: | 10.1073/pnas.0408004102 |