η6-Type anion-π in biomolecular recognition

Theoretical and compelling experimental evidence indicates that the interaction between an anion and an aromatic p system when the anion is directly above the ring face (eta(6)-type anion-pi), can be attractive. This may play an important role in the formation and recognition of biomolecular structures. We examined high-resolution structures of proteins and nucleic acids for the presence of eta(6)-type anion-pi. Though less frequent than its counterpart cation-pi, eta(6)-type anion-pi is observed unambiguously, occurring in protein/nucleic acid loops and often involving conserved/coevolving sites in proteins, suggesting it plays an important role in macromolecular folding and function. (C) 2012 Federation of European Biochemical Societies. Published by Elsevier B. V. All rights reserved.