Student Research: Christine Bellas

, , 2001
Faculty Advisor: David L. Eaton

Identification and Characterization of a Human Gltathione S-transferase M2-2


Abstract

Glutathione S-transferases (GSTs, E.C. 2.5 1.18) are a multi-gene family of dimeric enzymes that detoxify a wide variety of electrophilic compounds by conjugating them with reduced glutathione. One form, human GSTM2-2 (hGSTM2-2) has been found to be particularly efficient at catalyzing the conjugation of glutathione with o-quinones derived from the physiologically based catecholamines. Since the physiological oxidation of catecholamines to o-quinones gives rise to redox cycling and neurotoxicity, the conjugation of o-quinones with glutathione may reduce endogenous oxidative tissue damage in the brain. This may protect against the onset of neurodegenerative diseases such as Parkinson's disease. Three single nucleotide polymorphisms in the hGSTM2 gene have been identified. The first was a T to C transition in codon 74 that did not result in an amino acid change. The second was an A to G transition in the splice acceptor site of intron 7 that changed the splice acceptor consensus sequence AG to GG. The third was a G to T transition in codon 201 which results in a non-conservative serine to isoleucine change (Ser201Ile). The Ser201Ile-hGSTM2-2 variant cDNA was produced by site-directed mutagenesis of WT cDNA, and the variant enzyme expressed and purified together with the WT enzyme. The variant and WT enzymes were characterized for enzymatic activity on several substrates. The Ser201Ile substitution had little effect on the catalytic activity hGSTM2-2 towards synthetic substrates or the physiological substrate aminochrome. Since the Ser201Ile-hGSTM2-2 variant metabolizes aminochrome at similar rates as the wild type enzyme, it appears unlikely that the variant significantly modulates and individual's susceptibility towards neurodegenerative diseases such as Parkinson's disease.

Taken from the beginning of thesis.