BIOL 182 |
| Computational chemistry combined with multiple intrinsic kinetic isotope effects provide atomic maps of substrates at their transition states in their cognate enzymes. Closely related purine nucleoside phosphorylases (PNPs) have distinct transition states. These structures of enzymatic transition states are being used to produce transition state analogues as specific enzymatic inhibitors. Immucillin-H is similar to the transition state of inosine in bovine PNP and has Kd values of 23 and 56 pM for bovine and human PNPs, respectively. DADMe-Immucillin-H was designed to mimic the transition state structure of 2'-deoxy-inosine at the transition state of human PNP and has Kd values of 16 and 110 pM for human and bovine PNPs, respectively. Distinct transition state structures are possible despite complete identity of catalytic site residues in these enzymes. We hypothesize that transition state differences reside in the protein dynamic vibrational architecture remote from the catalytic sites. Mutations of remote residues differing between human and bovine PNP alter Kd values for the Immucillins, providing experimental support for dynamic differences in transition state interactions. |
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Repligen Award Symposium: Enzymatic Catalysis and Transition States
1:30 PM-4:40 PM, Wednesday, 13 September 2006 Moscone Center -- Room 238, Oral
Division of Biological Chemistry |