Role of solvent in determining conformational preferences of alanine dipeptide in water

被引:145
作者
Drozdov, AN
Grossfield, A
Pappu, RV
机构
[1] Washington Univ, Dept Biomed Engn, St Louis, MO 63130 USA
[2] Washington Univ, Ctr Computat Biol, St Louis, MO 63130 USA
[3] Washington Univ, Sch Med, Dept Biochem & Mol Biophys, St Louis, MO 63110 USA
[4] Washington Univ, Sch Med, Ctr Computat Biol, St Louis, MO 63110 USA
关键词
D O I
10.1021/ja039051x
中图分类号
O6 [化学];
学科分类号
0703 ;
摘要
Evidence from a variety of spectroscopic probes indicates that (phi, psi) values corresponding to the left-handed polyproline II helix (P-II) are preferred for short alanine-based peptides in water. On the basis of results from theoretical studies, it is believed that the observed preference is dictated by favorable pepticle-solvent interactions, which are realized through formation of optimal hydrogen-bonding water bridges between peptide donor and acceptor groups. In the present study, we address this issue explicitly by analyzing the hydration structure and thermodynamics of 16 low-energy conformers of the alanine dipeptide (N-acetylalanine-Ar-methylamide) in liquid water. Monte Carlo simulations in the canonical ensemble were performed under ambient conditions with all-atom OPLS parameters for the alanine dipeptide and the TIP5P model for water. We find that the number of hydrogen-bonded water molecules connecting the peptide group donor and acceptor atoms has no effect on the solvation thermodynamics. Instead, the latter are determined by the work done to fully hydrate the peptide. This work is minimal for conformations that are characterized by a minimal overlap of the primary hydration shells around the peptide donor and acceptor atoms. As a result, pepticle-solvent interactions favor "compact" conformations that do not include P-II-like geometries. Our main conclusion is that the experimentally observed preference for P-II does not arise due to favorable direct interactions between the peptide and water molecules. Instead, the latter act to unmask underlying conformational preferences that are a consequence of minimizing intrapeptide steric conflicts.
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页码:2574 / 2581
页数:8
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