A Theoretical Model for the Folding/Unfolding Thermodynamics of Single-Domain Proteins, Based on the Quasi-Gaussian Entropy Theory

Danilo Roccatano, A. Di Nola, and Andrea Amadei*

School of Engineering and Science, International University Bremen, Campus Ring 1, D-28725 Bremen, Germany, Dipartimento di Chimica Universita` di Roma "La Sapienza" P.le A. Moro 5, 00185 Roma, Italy, and Dipartimento di Scienze e Tecnologie Chimiche Universita` di Roma "Tor Vergata", via della Ricerca Scientifica 1, I-00133 Roma, Italy

Received: November 25, 2003
In Final Form: February 19, 2004

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Abstract:

The quasi-Gaussian entropy (QGE) theory was used to formulate a statistical mechanical model describing the thermodynamics of the folding/unfolding process of single-domain proteins. The model was parametrized using experimental data obtained from differential scanning calorimetry (DSC) of a set of proteins. The results showed that the model is able to reproduce the experimental behavior in the usual temperature range, for all the analyzed proteins. Furthermore, a remarkable similarity of some parameters of the model, when normalized per residue and corresponding to well-defined physical properties, was found. Interestingly, at low temperature, the model provides cold denaturation features for all the proteins. Finally, a general description of the folding/unfolding process and stability, based on the physical view provided by the model, is discussed.