Dresden 2006 – scientific programme
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AKB: Biologische Physik
AKB 19: Proteins
AKB 19.2: Talk
Wednesday, March 29, 2006, 16:15–16:30, ZEU 260
On the balance of the enthalpic and the entropic contributions to the stability of the helix: A DFT-GGA study — •Lars Ismer1, Joel Ireta1, Matthias Scheffler1, and Jörg Neugebauer2 — 1Fritz-Haber-Insitut der Max-Planck-Gesellschaft, Faradayweg 4-6, D-14195 Berlin — 2Max-Planck-Institut für Eisenforschung, Max-Planck-Strasse 1, D-40237 Düsseldorf
Accurate theoretical studies of the thermodynamic stability of isolated peptide chains may serve as a reliable reference to understand the stability of the secondary structure of proteins. We have therefore calculated the free energy difference needed to fold the fully extended structure (FES) of isolated, infinite polyalanine (Ala) and -glycine (Gly) chains into various helical conformations such as the 310-, α-, and π-helix. The calculations were done by employing DFT-GGA, plane waves, pseudopotentials and the quasi-harmonic approximation to estimate the finite temperature effects. We find that entropic contributions to the free energy strongly reduce the enthalpic stability of the helices at elevated temperatures, leading to a transition to the FES at Tc ∼ 460 K for Ala and Tc ∼ 400 K for Gly. Below Tc the α-helix is the conformation with the lowest free energy. The π-helix shows the strongest temperature dependence resulting in a significant destabilization with respect to the α- and 310-helix for T > 0 K. A detailed analysis showed these thermodynamic trends to be intrinsic features of the specific hydrogen bonding network formed by the various helices and to be largely independent of the specific amino acid.