This research program addresses two major and current problems in infectious disease using novel technology. Toxin-directed transition state inhibitors offer a new approach to prevent the damage of bacterial exotoxins to human tissues. Antibiotic resistance is a global problem in infectious disease. Tissue- protective toxin inhibitors could act as antibiotics which are not expected to elicit resistance in the causitive organisms. The experimental approach is to use the frontier method of enzymatic transition state analysis and to apply it to the action of bacterial exotoxins. ADP-ribosylating bacterial exotoxins catalyze the covalent modification of GTP-binding proteins. Cholera, diphtheria and pertussis toxins ADP-ribosylate Gsalpha, eukaryotic elongation factor 2, and Gialpha proteins, respectively. Transition state analysis of bacterial ADP-ribosylating exotoxins will be used to design transition state inhibitors against cholera, diphtheria, pertussis and related exotoxins. Transition-state inhibitors against bacterial exotoxins are expected to protect against the exotoxins and thus ameliorate the damage caused in these childhood and endemic diseases. Transition state structure is determined by measuring kinetic isotope effects with NAD+ substrate labeled in all of the atomic positions expected to undergo bonding changes as bonds are broken and made at the enzyme-stabilized transition state. The ADP- ribosylated G-protein is analyzed for the isotopic discrimination of the incorporated ADP-ribose. The isotope effects are then corrected to reveal the full chemical expression of intrinsic isotope effects. An atomic model of all atoms at least two bonds from the reaction center is constructed which is constrained by the values of the kinetic isotope effects. Semiemperical and ab initio methods are used to complete the structure of the transition state molecules, with constraints at every step to comply with the experimental kinetic isotope effects. Transition state structures are mapped using the molecular electrostatic potential surface at the van der Waals radius and compared to that of the substrate. The relationship provides predictive value for transition state inhibitor design. Molecules with electronic similarity close to that of the transition state are synthesized and tested as transition state inhibitors. These procedures have resulted in the discovery of novel transition state inhibitors for several simple enzymatic reactions. The goal of this work is to extend transition state inhibitor design to the complex reactions catalyzed by bacterial ADP-ribosylating toxins.

Agency
National Institute of Health (NIH)
Institute
National Institute of Allergy and Infectious Diseases (NIAID)
Type
Research Project (R01)
Project #
5R01AI034342-09
Application #
6497266
Study Section
Biochemistry Study Section (BIO)
Program Officer
Klein, David L
Project Start
1993-07-01
Project End
2004-01-31
Budget Start
2002-02-01
Budget End
2003-01-31
Support Year
9
Fiscal Year
2002
Total Cost
$427,735
Indirect Cost
Name
Albert Einstein College of Medicine
Department
Biochemistry
Type
Schools of Medicine
DUNS #
009095365
City
Bronx
State
NY
Country
United States
Zip Code
10461
Schramm, Vern L (2005) Enzymatic transition states: thermodynamics, dynamics and analogue design. Arch Biochem Biophys 433:13-26
Parikh, Sapan L; Schramm, Vern L (2004) Transition state structure for ADP-ribosylation of eukaryotic elongation factor 2 catalyzed by diphtheria toxin. Biochemistry 43:1204-12
Zhou, Guo-Chun; Parikh, Sapan L; Tyler, Peter C et al. (2004) Inhibitors of ADP-ribosylating bacterial toxins based on oxacarbenium ion character at their transition states. J Am Chem Soc 126:5690-8
Sauve, Anthony A; Schramm, Vern L (2003) Sir2 regulation by nicotinamide results from switching between base exchange and deacetylation chemistry. Biochemistry 42:9249-56
Sauve, Anthony A; Schramm, Vern L (2002) Mechanism-based inhibitors of CD38: a mammalian cyclic ADP-ribose synthetase. Biochemistry 41:8455-63
Sauve, A A; Celic, I; Avalos, J et al. (2001) Chemistry of gene silencing: the mechanism of NAD+-dependent deacetylation reactions. Biochemistry 40:15456-63
Berti, P J (1999) Determining transition states from kinetic isotope effects. Methods Enzymol 308:355-97
Braunheim, B B; Miles, R W; Schramm, V L et al. (1999) Prediction of inhibitor binding free energies by quantum neural networks. Nucleoside analogues binding to trypanosomal nucleoside hydrolase. Biochemistry 38:16076-83
Sauve, A A; Munshi, C; Lee, H C et al. (1998) The reaction mechanism for CD38. A single intermediate is responsible for cyclization, hydrolysis, and base-exchange chemistries. Biochemistry 37:13239-49
Scheuring, J; Berti, P J; Schramm, V L (1998) Transition-state structure for the ADP-ribosylation of recombinant Gialpha1 subunits by pertussis toxin. Biochemistry 37:2748-58

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