The present study characterized conserved residues in a GST (glutathione transferase) in the active-site region that interacts with glutathione. This region of the active site is near the glycine moiety of glutathione and consists of a hydrogen bond network. In the GSTD (Delta class GST) studied, adGSTD4-4, the network consisted of His38, Met39, Asn47, Gln49, His50 and Cys51. In addition to contributing to glutathione binding, this region also had major effects on enzyme catalysis, as shown by changes in kinetic parameters and substrate-specific activity. The results also suggest that the electron distribution of this network plays a role in stabilization of the ionized thiol of glutathione as well as impacting on the catalytic rate-limiting step. This area constitutes a second glutathione active-site network involved in glutathione ionization distinct from a network previously observed interacting with the glutamyl end of glutathione. This second network also appears to be functionally conserved in GSTs. In the present study, His50 is the key basic residue stabilized by this network, as shown by up to a 300-fold decrease in kcat and 5200-fold decrease in kcat/Km for glutathione. Although these network residues have a minor role in structural integrity, the replaced residues induced changes in active-site topography as well as generating positive co-operativity towards glutathione. Moreover, this network at the glycine moiety of GSH (glutathione) also contributed to the ‘base-assisted deprotonation model’ for GSH ionization. Taken together, the results indicate a critical role for the functionally conserved basic residue His50 and this hydrogen bond network in the active site.
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Research Article|
August 13 2007
A functionally conserved basic residue in glutathione transferases interacts with the glycine moiety of glutathione and is pivotal for enzyme catalysis
Ardcharaporn Vararattanavech;
Ardcharaporn Vararattanavech
1Institute of Molecular Biology and Genetics, Mahidol University, Salaya Campus, 25/25 Putthamonthol Road 4, Salaya, Nakon Pathom 73170, Thailand
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Albert J. Ketterman
Albert J. Ketterman
1
1Institute of Molecular Biology and Genetics, Mahidol University, Salaya Campus, 25/25 Putthamonthol Road 4, Salaya, Nakon Pathom 73170, Thailand
1To whom correspondence should be addressed (email albertketterman@yahoo.com).
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Publisher: Portland Press Ltd
Received:
March 27 2007
Revision Received:
May 22 2007
Accepted:
May 24 2007
Accepted Manuscript online:
May 24 2007
Online ISSN: 1470-8728
Print ISSN: 0264-6021
© The Authors Journal compilation © 2007 Biochemical Society
2007
Biochem J (2007) 406 (2): 247–256.
Article history
Received:
March 27 2007
Revision Received:
May 22 2007
Accepted:
May 24 2007
Accepted Manuscript online:
May 24 2007
Citation
Ardcharaporn Vararattanavech, Albert J. Ketterman; A functionally conserved basic residue in glutathione transferases interacts with the glycine moiety of glutathione and is pivotal for enzyme catalysis. Biochem J 1 September 2007; 406 (2): 247–256. doi: https://doi.org/10.1042/BJ20070422
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