Flexibility of the GSTT2-2 Enzyme

   
               
Principal Investigator

Gareth Chelvanayagam

Division of Molecular Medicine,John Curtin School of Medical Research

Co-Investigators

Jack Flanagan

Philip Board

Division of Molecular Medicine, John Curtin School of Medical Research

Projects

x07 - PC, VPP

The glutathione transferases (GSTs) are a
superfamily of enzymes responsible for the
conjugation of the tripeptide GSH to generally toxic second substrates capable of causing damage to other cellular macromolecules such as DNA. This renders the toxic substrates more hydrophillic and consequently, less likely to cause cellular damage. Furthermore, the conjugation of GSH provides the cell with a metabolic handle through which it can proccess these toxins and finally transport them from the cell. The GSTs catalyse the conjugation of GSH by reducing the pKa of the cysteinyl thiol moiety of GSH allowing it to form the thiolate anion which it can then stabilize. Stabilization of the thiolate is carried out by a conserved N terminal domain hydroxyl group, however the donor residue for this group is not conserved. Of the four classes that have been the subject of most mechanistic studies, three classes (Alpha, Mu and Pi) utilize a Tyr hydroxyl, whereas the Theta class enzymes utilize a Ser hydroxyl.

The flexibility of the GSTT2-2 enzyme is of interest as the x-ray crystal structure of this enzyme did not provide any physical clues as to how substrates entered the active site despite the fact that the crystals were catalytically active. Experimental results have pointed to a region which potentially causes increased flexibility and faster substrate and product flux, indicating that this is also a very important feature of the enzyme's mechanistic study.

     
         
               

       
               
What are the results to date and the future work?

So far only preliminary work has begun on this project and most of our efforts have been directed towards our related project on the mechanism of the GSTT2 enzyme. Nonetheless, several design parameters of the system have been established and calculations will commence shortly.

Insights from this work have assisted us in the construction of an homology model for the related GSTT1 enzyme, including the identification of amino acids likely to be involved in the reaction mechanism.

               
- Appendix A

 
               

       
What computational techniques are used?

So far this project has made use of the conventional molecular dynamics packages without any modification.

Publications

Flanagan, J.U., Rossjohn, J., Parker, M.W., Board, P.G., and Chelvanayagam, G., A homology model for the Human Theta-Class Glutathione Transferase T1-1, Proteins: Structure, Function, Genetics., 33:444-454 (1998).

       
Appendix A -