Role of the sulfonium center in determining the ligand specificity of human s-adenosylmethionine decarboxylase.
Publication Type:Journal Article
Source:Biochemistry, Volume 48, Issue 27, p.6423-30 (2009)
Keywords:Adenosylmethionine Decarboxylase, Crystallography, X-Ray, Humans, Kinetics, Ligands, Protein Conformation, Quantum Theory, Substrate Specificity, Sulfonium Compounds, Thermodynamics
<p>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-methyladenosine. The crystal structures revealed a favorable cation-pi 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-pi interaction.</p>