Quantification of Cation–π Interactions in Protein–Ligand Complexes: Crystal‐Structure Analysis of Factor Xa Bound to a Quaternary Ammonium Ion Ligand

Abstract

The aromatic box formed by the side chains Phe 174, Tyr 99, and Trp 215 in the S4-pocket of Factor Xa is a very effective onium binding site (see picture; red O, blue N, green Cligand, gray Cprotein). The free enthalpy increment for cation–π interactions between quaternary ammonium ions and aromatic groups in this box is determined to be ΔΔG=2.8 kcal mol−1. Database searches reveal that similar cation binding sites are not uncommon in biological systems. Supporting information for this article is available on the WWW under http://www.wiley-vch.de/contents/jc_2002/2005/z500883_s.pdf or from the author. Please note: The publisher is not responsible for the content or functionality of any supporting information supplied by the authors. Any queries (other than missing content) should be directed to the corresponding author for the article.