Evidence of complete hydrophobic coating of bombesin by trifluoroethanol in aqueous solution: an NMR spectroscopic and molecular dynamics study.
Bombesin is a tetradecapeptide that possesses a random coil structure in pure water. In the presence of 30 % (v/v) 2,2,2-trifluoroethanol (TFE), it adopts a partial helical conformation involving the C-terminal amino acids 6-14. This conformational change, known as the TFE effect, is studied here in terms of the solvation state of the peptide at different TFE concentrations by means of intermolecular homo- and heteronuclear NOE measurements. When an aqueous solution of bombesin is titrated with TFE, a continual decrease in the water/peptide interactions and a concomitant increase in the TFE/peptide interactions is observed, and at 30 % (v/v) TFE no homonuclear NOEs between water and the peptide can be detected. The conformational transition of the bombesin molecule is thus accompanied by a complete surface covering with TFE. A parallel molecular dynamics (MD) study of the peptide in aqueous solution with the single-point charge (SPC) water model and in a 30 % (v/v) TFE/water mixture with a recently developed TFE model has also been performed. The 10 ns simulations were in agreement with the experimental data. The calculations indicate stabilisation of the alpha-helix in the H(2)O/TFE mixture, in contrast to the situation in pure water, and clustering of the TFE molecules around the peptide.
Díaz
M Dolores
MD
Institut für Analytische Chemie, Universität Leipzig Linnéstrasse 3, 04103 Leipzig, Germany.
Fioroni
M
M
Burger
K
K
Berger
Stefan
S
D000595:Amino Acid Sequence; D001839:Bombesin / Q000737:chemistry*; D057927:Hydrophobic and Hydrophilic Interactions; D007700:Kinetics; D009682:Magnetic Resonance Spectroscopy; D015394:Molecular Structure; D011487:Protein Conformation; D012996:Solutions / Q000737:chemistry; D012997:Solvents / Q000737:chemistry; D013057:Spectrum Analysis; D014270:Trifluoroethanol / Q000737:chemistry*
D012996:Solutions; D012997:Solvents; D014270:Trifluoroethanol; D001839:Bombesin