Dresden 2011 – wissenschaftliches Programm

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MO: Fachverband Molekülphysik

MO 1: Biomolecules

MO 1.9: Vortrag

Montag, 14. März 2011, 12:30–12:45, TOE 317

The impact of Li⁺ ions on the conformation of the prolyl-peptide bond — •Carsten Baldauf, Volker Blum, and Matthias Scheffler — Fritz-Haber-Institut der MPG, Faradayweg 4-6, D-14195 Berlin-Dahlem, Germany

Proline has a special role amongst the canonical amino acids. Within a peptide chain, the stabilities of the cis and trans state of the prolyl-peptide bond are very similar, but they are separated by a high barrier. Prolyl-cis-trans isomerization is under discussion as molecular timer for protein (re)folding. Li⁺ ions can change the cis/trans ratio of model peptides.[1,2] We here present a comparative study of the impact of the monovalent cations Li⁺ and Na⁺ on the conformation of the model peptide Ac-AlaAlaProAla-NMe (AAPA). The conformational space of the system is pre-screened with a force field-based sampling approach and further refined with density functional theory (DFT) calculations for a wide range of the minima found. We observe drastic discrepancies between energy hierarchies from popular force fields and from DFT (van der Waals corrected PBE functional),[3] demonstrating that both Li⁺ and Na⁺ must be treated much more carefully than with a simple force field to assess their true role in shaping peptide conformations. Li⁺ can induce a ribbon-like conformation of AAPA without H-bonding but stabilized by cations bridging between backbone carbonyl oxygens.

[1] Reimer U et al. J Mol Biol. 1998; 279:449. [2] Kofron JL et al. Biochemistry. 1991; 30:6127. [3] Tkatchenko A, Scheffler M. Phys Rev Lett. 2009; 102:073005.