Details

Autor(en) / Beteiligte

• Tsai, Midas (I-Hsien)
• Xu, Yujia
• Dannenberg, J. J

Titel

Ramachandran Revisited. DFT Energy Surfaces of Diastereomeric Trialanine Peptides in the Gas Phase and Aqueous Solution

Ist Teil von

• The journal of physical chemistry. B, 2009-01, Vol.113 (1), p.309-318

Ort / Verlag

United States: American Chemical Society

Erscheinungsjahr

2009

Quelle

MEDLINE

Beschreibungen/Notizen

• We report DFT calculations at the B3LYP/D95(d,p) level on the gas phase, aqueous solvation and solvated energies as functions of the central ψ and ϕ dihedral angles (in steps of 5° each) of acetyl-LAla-LAla-LAla-NH2 (3AL) and its diastereomer, acetyl-LAla-DAla-LAla-NH2 (3AD). In addition to structures without internal H-bonds (C5 interactions are neglected), many (95) structures containing internal H-bonds were completely optimized. The only minima for non-H-bonding structures in the gas phase correspond to extended β-strands for both diastereomers. Some (but not all) structures with internal H-bonds are more stable than those without them. The energy landscapes for the solvated species show multiple minima for the non-H-bonding species and a single minimum for the H-bonding species (310-helix), suggesting that the equilibrium conformational mixture in water be composed of the extended β-strand, polyproline II, 310-helix, and α-helix-like (with no H-bonds) conformations which are all within about 1 kcal/mol of each other. Most H-bonding structures are destabilized relative to the non-H-bonding structures in aqueous solution, but some with large dipole moments are not. The large dipole moment of the α-helix-like conformation leads to its increased stability in water (vs the gas phase). Significant qualitative and quantitative differences are reported for the energy landscapes of the two diastereomers when one is compared with the mirror image of the other landscape (particularly in the β-turn region), suggesting that the differences in the energies of the unfolded peptides need to be considered when considering the stabilities of folded peptides and proteins with single amino acid mutations.