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Thermodynamic consequences of Tyr to Trp mutations in the cation-π-mediated binding of trimethyllysine by the HP1 chromodomain.

  • Author(s): Krone, Mackenzie W
  • Albanese, Katherine I
  • Leighton, Gage O
  • He, Cyndi Qixin
  • Lee, Ga Young
  • Garcia-Borràs, Marc
  • Guseman, Alex J
  • Williams, David C
  • Houk, KN
  • Brustad, Eric M
  • Waters, Marcey L
  • et al.

Evolution has converged on cation-π interactions for recognition of quaternary alkyl ammonium groups such as trimethyllysine (Kme3). While computational modelling indicates that Trp provides the strongest cation-π interaction of the native aromatic amino acids, there is limited corroborative data from measurements within proteins. Herein we investigate a Tyr to Trp mutation in the binding pocket of the HP1 chromodomain, a reader protein that recognizes Kme3. Binding studies demonstrate that the Trp-mediated cation-π interaction is about -5 kcal mol-1 stronger, and the Y24W crystal structure shows that the mutation is not perturbing. Quantum mechanical calculations indicate that greater enthalpic binding is predominantly due to increased cation-π interactions. NMR studies indicate that differences in the unbound state of the Y24W mutation lead to enthalpy-entropy compensation. These results provide direct experimental quantification of Trp versus Tyr in a cation-π interaction and afford insight into the conservation of aromatic cage residues in Kme3 reader domains.

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