Role of the sulfonium center in determining the ligand specificity of human s-adenosylmethionine decarboxylase.
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.
Bale
Shridhar
S
Department of Chemistry and Chemical Biology, Cornell University, Ithaca, New York 14853, USA.
Brooks
Wesley
W
Hanes
Jeremiah W
JW
Mahesan
Arnold M
AM
Guida
Wayne C
WC
Ealick
Steven E
SE
D012437:Adenosylmethionine Decarboxylase / Q000737:chemistry / Q000378:metabolism*; D018360:Crystallography, X-Ray; D006801:Humans; D007700:Kinetics; D008024:Ligands; D011487:Protein Conformation; D011789:Quantum Theory; D013379:Substrate Specificity; D013452:Sulfonium Compounds / Q000378:metabolism*; D013816:Thermodynamics
D008024:Ligands; D013452:Sulfonium Compounds; D012437:Adenosylmethionine Decarboxylase