Simple Cation−π Interaction between a Phenyl Ring and a Protonated Amine Stabilizes an α-Helix in Water

Lun K. Tsou, Chad D. Tatko, and Marcey L. Waters*
Contribution from the Department of Chemistry, Venable and Kenan Laboratories, CB 3290, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina 27599
J. Am. Chem. Soc., 2002, 124 (50), pp 14917–14921
DOI: 10.1021/ja026721a
Publication Date (Web): November 22, 2002
Copyright © 2002 American Chemical Society
*

 To whom correspondence should be addressed. E-mail:  mlwaters@ email.unc.edu.

Abstract

Abstract Image

Cation−π interactions have been proposed to be important contributors to protein structure and function. In particular, these interactions have been suggested to provide significant stability at the solvent-exposed surface of a protein. We have investigated the magnitude of cation−π interactions between phenylalanine (Phe) and lysine (Lys), ornithine (Orn), and diaminobutanoic acid (Dab) in the context of an α-helix and have found that only the Phe···Orn interaction provides significant stability to the helix, stabilizing it by −0.4 kcal/mol. This interaction energy is in the same range as a salt bridge in an α-helix, and equivalent to the recently reported Trp···Arg interaction in an α-helix, despite the fact that Trp···guanidinium interactions have been proposed to be stronger than Phe···ammonium interactions. These results indicate that even the simplest cation−π interaction can provide significant stability to protein structure and demonstrate the subtle factors that can influence the observed interaction energies in designed systems.

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History

  • Published In Issue December 18, 2002
  • Received April 29, 2002

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