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BP: Fachverband Biologische Physik

BP 23: Biopolymers

BP 23.2: Vortrag

Donnerstag, 25. März 2010, 10:30–10:45, H43

(Un)folding of a high-temperature stable polyalanine helix from first principles — •Volker Blum, Mariana Rossi, Alex Tkatchenko, and Matthias Scheffler — Fritz-Haber-Institut der Max-Planck-Gesellschaft, D-14195 Berlin

Peptides in vacuo offer a unique, well-defined testbed to match experiments directly against first-principles approaches that predict the intramolecular interactions that govern peptide and protein folding. In this respect, the polyalanine-based peptide Ac-Ala₁₅-LysH⁺ is particularly interesting, as it is experimentally known to form helices in vacuo, with stable secondary structure up to ≈ 750 K [1]. Room-temperature folding and unfolding timescales are usually not accessible by direct first-principles simulations, but this high T scale allows a rare direct first-principles view. We here use van der Waals corrected [2] density functional theory in the PBE generalized gradient approximation as implemented in the all-electron code FHI-aims [3] to show by Born-Oppenheimer ab initio molecular dynamics that Ac-Ala₁₅-LysH⁺ indeed unfolds rapidly (within a few ps) at T=800 K and 1000 K, but not at 500 K. We show that the structural stability of the α helix at 500 K is critically linked to a correct van der Waals treatment, and that the designed LysH⁺ ionic termination is essential for the observed helical secondary structure. [1] M. Kohtani et al., JACS 126, 7420 (2004). [2] A. Tkatchenko, M. Scheffler, PRL 102, 073005 (2009). [3] V. Blum et al., Comp. Phys. Comm. 180, 2175 (2009).