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Protein Science (2001), 10:2075-2082.
Copyright © 2001 The Protein Society

Hydrogen-bonding classes in proteins and their contribution to the unfolding reaction

Raffaele Ragone

Dipartimento di Biochimica e Biofisica and CRISCEB, Seconda Universit{alpha}ave; di Napoli, 80138 Naples, Italy

Reprint request to: Raffaele Ragone, Dipartimento di Biochimica e Biofisica and CRISCEB, Seconda Universit{alpha}ave; di Napoli, Via Costantinopoli 16, 80138 Naples, Italy; e-mail: ragone{at}unina2.it; fax: 390-81-294136.

This paper proposes to assess hydrogen-bonding contributions to the protein stability, using a set of model proteins for which both X-ray structures and calorimetric unfolding data are known. Pertinent thermodynamic quantities are first estimated according to a recent model of protein energetics based on the dissolution of alkyl amides. Then it is shown that the overall free energy of hydrogen-bond formation accounts for a hydrogen-bonding propensity close to helix-forming tendencies previously found for individual amino acids. This allows us to simulate the melting curve of an alanine-rich helical 50-mer with good precision. Thereafter, hydrogen-bonding enthalpies and entropies are expressed as linear combinations of backbone-backbone, backbone–side-chain, side-chain–backbone, and side-chain–side-chain donor-acceptor contributions. On this basis, each of the four components shows a different free energy versus temperature trend. It appears that structural preference for side-chain–side-chain hydrogen bonding plays a major role in stabilizing proteins at elevated temperatures.

Keywords: Group additivity; hydrophobic interaction; N-alkyl amides; packing interactions; protein thermodynamics; thermostability


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