4l7k

Publication Abstract from PubMed

Although the cation-pi pair, formed between a side chain or substrate cation and the negative electrostatic potential of a pi system on the face of an aromatic ring, has been widely discussed and has been shown to be important in protein structure and protein-ligand interactions, there has been little discussion of the potential structural and functional importance in proteins of the related anion-aromatic pair (i.e., interaction of a negatively charged group with the positive electrostatic potential on the ring edge of an aromatic group). We posited, based on prior structural information, that anion-aromatic interactions between the anionic Asp general base and Phe54 and Phe116 might be used instead of a hydrogen-bond network to position the general base in the active site of ketosteroid isomerase from Comamonas testosteroni as there are no neighboring hydrogen-bonding groups. We have tested the role of the Phe residues using site-directed mutagenesis, double-mutant cycles, and high-resolution X-ray crystallography. These results indicate a catalytic role of these Phe residues. Extensive analysis of the Protein Data Bank provides strong support for a catalytic role of these and other Phe residues in providing anion-aromatic interactions that position anionic general bases within enzyme active sites. Our results further reveal a potential selective advantage of Phe in certain situations, relative to more traditional hydrogen-bonding groups, because it can simultaneously aid in the binding of hydrophobic substrates and positioning of a neighboring general base.

Use of anion-aromatic interactions to position the general base in the ketosteroid isomerase active site.,Schwans JP, Sunden F, Lassila JK, Gonzalez A, Tsai Y, Herschlag D Proc Natl Acad Sci U S A. 2013 Jul 9;110(28):11308-13. doi:, 10.1073/pnas.1206710110. Epub 2013 Jun 24. PMID:23798413^[1]

From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine.