3CSI

Crystal Structure of the Glutathione Transferase Pi allelic variant*C, I104V/A113V, in complex with the Chlorambucil-Glutathione Conjugate

Summary for 3CSI

• Entry DOI: 10.2210/pdb3csi/pdb
• Related: 3CSH 3CSJ
• Descriptor: Glutathione S-transferase P, CHLORIDE ION, 2-(N-MORPHOLINO)-ETHANESULFONIC ACID, ... (9 entities in total)
• Functional Keywords: transferase, glutathione, detoxification, chlorambucil, allelic variant
• Biological source: Homo sapiens (human)
• Total number of polymer chains: 4
• Total formula weight: 97575.81

Authors

Parker, L.J. (deposition date: 2008-04-09, release date: 2008-07-01, Last modification date: 2023-08-30)

Primary citation

Parker, L.J.,Ciccone, S.,Italiano, L.C.,Primavera, A.,Oakley, A.J.,Morton, C.J.,Hancock, N.C.,Bello, M.L.,Parker, M.W.
The anti-cancer drug chlorambucil as a substrate for the human polymorphic enzyme glutathione transferase P1-1: kinetic properties and crystallographic characterisation of allelic variants.
J.Mol.Biol., 380:131-144, 2008

PubMed Abstract: The commonly used anti-cancer drug chlorambucil is the primary treatment for patients with chronic lymphocytic leukaemia. Chlorambucil has been shown to be detoxified by human glutathione transferase Pi (GST P1-1), an enzyme that is often found over-expressed in cancer tissues. The allelic variants of GST P1-1 are associated with differing susceptibilities to leukaemia and differ markedly in their efficiency in catalysing glutathione (GSH) conjugation reactions. Here, we perform detailed kinetic studies of the allelic variants with the aid of three representative co-substrates. We show that the differing catalytic properties of the variants are highly substrate-dependent. We show also that all variants exhibit the same temperature stability in the range 10 degrees C to 45 degrees C. We have determined the crystal structures of GST P1-1 in complex with chlorambucil and its GSH conjugate for two of these allelic variants that have different residues at positions 104 and 113. Chlorambucil is found to bind in a non-productive mode to the substrate-binding site (H-site) in the absence of GSH. This result suggests that under certain stress conditions where GSH levels are low, GST P1-1 can inactivate the drug by sequestering it from the surrounding medium. However, in the presence of GSH, chlorambucil binds in the H-site in a productive mode and undergoes a conjugation reaction with GSH present in the crystal. The crystal structure of the GSH-chlorambucil complex bound to the *C variant is identical with the *A variant ruling out the hypothesis that primary structure differences between the variants cause structural changes at the active site. Finally, we show that chlorambucil is a very poor inhibitor of the enzyme in contrast to ethacrynic acid, which binds to the enzyme in a similar fashion but can act as both substrate and inhibitor.

PubMed: 18511072
DOI: 10.1016/j.jmb.2008.04.066

Experimental method

X-RAY DIFFRACTION (1.9 Å)