Steve Ealick's Research Group

Abstract:

Bale S, Guida WC, Brooks WH, Hanes JW, Mahesan AM and Ealick SE. Role of the Sulfonium Center in Determining Ligand Specificity of Human S-Adenosylmethionine Decarboxylase. Biochemistry 48:6423-6430 (2009)

S-Adenosylmethionine decarboxylase (AdoMetDC) is a key enzyme in the polyamine biosynthetic pathway. Inhibition of this pathway and subsequent depletion of polyamine levels is a viable strategy for cancer chemotherapy and for the treatment of parasitic diseases. Substrate analogue inhibitors display an absolute requirement for a positive charge at the position equivalent to the sulfonium of S-adenosylmethionine. We investigated the ligand specificity of AdoMetDC through crystallography, quantum chemical calculations and stopped-flow experiments. We determined crystal structures of the enzyme cocrystallized with 5´-deoxy-5´-dimethylthioadenosine and 5´-deoxy-5´-(N-dimethyl)amino-8-methyl adenosine. The crystal structures revealed a favorable cation-π interaction between the ligand and the aromatic side chains of Phe7 and Phe223. The estimated stabilization from this interaction is 4.5 kcal/mol as determined by quantum chemical calculations. Stopped-flow kinetic experiments showed that the rate of the substrate binding to the enzyme greatly depends on Phe7 and Phe223, thus supporting the importance of the cation-π interaction.