Cation Binding by the Phenolate Group in Small Molecules and Proteins
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 sp^2 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 sp^2 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.
© 1994 American Chemical Society. Received August 4, 1993. The paper is dedicated to Professor C. N. R. Rao on the occasion of his 60th birthday. Support for the work (NCL Communication No. 5408) was provided by a grant from the Department of Science and Technology (India). We are grateful to Dr. D. C. Rees for encouragement and to Drs. E. N. Baker, N. Ito, and D. H. Ohlendorf for providing us with the atomic coordinates based on their work. We thank Mr. A. K. Gangopadhyay for assistance in the preparation of the manuscript.
Supplemental Material - ic00084a032_si_001.pdf