Cation binding by the phenolate group in small molecules and proteins

Abstract

The geometry of interactions of metal ions with the phenolate group in proteins and small molecules has been examined using coordinates listed in structural databases. Cations are found to avoid the sp² lone pair directions of the ligand oxygen; in small-molecule structures most of the cations are clustered close to the aromatic plane in the region between the sp² and the C-O vectors, whereas in proteins the ions move out of the plane. Such a spatial distribution is different from that observed for hydrogen-bonded neighbors interacting with a neutral tyrosine residue. The environment of a tyrosinate anion is such that it has a cation on one side of its plane and a hydrogen-bond donor on the other. Metal binding can disturb the normal conformation of the tyrosine side chain.