Crystal structure of a murine α-class glutathione S-transferase involved in cellular defense against oxidative stress

Glutathione S-transferases (GSTs) are ubiquitous multifunctional enzymes which play a key role in cellular detoxification. The enzymes protect the cells against toxicants by conjugating them to glutathione. Recently, a novel subgroup of α-class GSTs has been identified with altered substrate specificity which is particularly important for cellular defense against oxidative stress. Here, we report the crystal structure of murine GSTA4-4, which is the first structure of a prototypical member of this subgroup. The structure was solved by molecular replacement and refined to 2.9 Å resolution. It resembles the structure of other members of the GST superfamily, but reveals a distinct substrate binding site.

A subgroup of class α glutathione S-transferases Cloning of cDNA for mouse lung glutathione S-transferase GST 5.7

AbstractA full-length cDNA clone encoding the previously purified mouse glutathione S-transferase GST 5.7 [(1991), Biochem. J. 278, 793–799] has been isolated from a mouse lung cDNA library in λgt11. Sequencing of the clone revealed the presence of microheterogeneity in GST 5.7. Comparison of the deduced protein sequence with other glutathione S-transferases, together with previous information available on GST 5.7, indicates that the enzyme belongs to a novel subgroup within the α class of glutathione S-transferases. Members of the subgroup, which also include the rat GST 8-8 and perhaps chicken GST CL3, show high sequence homology with each other, but only moderate similarity to other α class enzymes. They share a substrate specificity profile that resembles π-class enzymes, and are active in the conjugation of lipid peroxidation products

The Cellular Distribution of Serotonin Transporter Is Impeded on Serotonin-Altered Vimentin Network

BACKGROUND:The C-terminus of the serotonin transporter (SERT) contains binding domains for different proteins and is critical for its functional expression. In endogenous and heterologous expression systems, our proteomic and biochemical analysis demonstrated that an intermediate filament, vimentin, binds to the C-terminus of SERT. It has been reported that 5HT-stimulation of cells leads to disassembly and spatial reorientation of vimentin filaments. METHODOLOGY/PRINCIPAL FINDINGS:We tested the impact of 5HT-stimulation on vimentin-SERT association and found that 5HT-stimulation accelerates the translocation of SERT from the plasma membrane via enhancing the level of association between phosphovimentin and SERT. Furthermore a progressive truncation of the C-terminus of SERT was performed to map the vimentin-SERT association domain. Deletion of up to 20, but not 14 amino acids arrested the transporters at intracellular locations. Although, truncation of the last 14 amino acids, did not alter 5HT uptake rates of transporter but abolished its association with vimentin. To understand the involvement of 5HT in phosphovimentin-SERT association from the plasma membrane, we further investigated the six amino acids between Delta14 and Delta20, i.e., the SITPET sequence of SERT. While the triple mutation on the possible kinase action sites, S(611), T(613), and T(616) arrested the transporter at intracellular locations, replacing the residues with aspartic acid one at a time altered neither the 5HT uptake rates nor the vimentin association of these mutants. However, replacing the three target sites with alanine, either simultaneously or one at a time, had no significant effect on 5HT uptake rates or the vimentin association with transporter. CONCLUSIONS/SIGNIFICANCE:Based on our findings, we propose that phosphate modification of the SITPET sequence differentially, one at a time exposes the vimentin binding domain on the C-terminus of SERT. Conversely, following 5HT stimulation, the association between vimentin-SERT is enhanced which changes the cellular distribution of SERT on an altered vimentin network

Cloning and expression of a novel Mu class murine glutathione transferase isoenzyme.

The present study describes the cDNA cloning, expression and characterization of a novel Mu class murine glutathione transferase (GST) isoenzyme. Screening of a cDNA library from the small intestine of a female A/J mouse using consensus probes derived from Mu class murine GST genes (mGSTM1-mGSTM5) resulted in the isolation of a full-length cDNA clone of a previously unknown Mu class GST gene (designated as mGSTM7). The choice of tissue was based on our previous identification in female A/J mouse small intestine of a potentially novel Mu class GST isoenzyme. The deduced amino acid sequence of mGSTM7, which comprises of 218 amino acid residues, exhibited about 67-78% identity with other Mu class murine GSTs. Recombinant mGSTM7-7 cross-reacted with anti-(GST Mu) antibodies, but not with anti-(GST Alpha) or anti-(GST Pi) antibodies. The pI and the reverse-phase-HPLC elution profile of recombinant mGSTM7-7 were different from those of other Mu class murine GSTs. The substrate specificity of mGSTM7-7 was also different compared with other Mu class murine GSTs. Interestingly, mGSTM7 had a higher identity with the human Mu class isoenzyme hGSTM4 (87% identity and 94% similarity in the amino acid sequence) than with any of the known mouse Mu class GSTs. Specific activities of recombinant mGSTM7-7 and human GSTM4-4 were comparable towards several substrates. For example, similar to hGSTM4-4, recombinant mGSTM7-7 was poorly active in catalysing the GSH conjugation of 1-chloro-2,4-dinitrobenzene and ethacrynic acid, and lacked activity towards 1,2-dichloro-4-nitrobenzene and 1,2-epoxy-3-(p-nitrophenoxy)propane. These results suggested that hGSTM4-4 might be the human counterpart of mouse GSTM7-7. Reverse transcription-PCR analysis using mGSTM7-specific primers revealed that mGSTM7 is widely expressed in tissues of female A/J mice, including liver, forestomach, lung, kidney, colon and spleen

Transport of glutathione-conjugates in human erythrocytes.

The last step of detoxification of both endogenous and environmental toxicants is typically a conjugation that produces a bulky hydrophilic molecule. The excretion of such conjugates out of cells is of sufficient biological importance to have led to the evolution of ATP-driven export pumps for this purpose. The substrate specificity of such transporters is broad, and in some cases it has been shown to include not only anionic conjugates but also neutral or weakly cationic drugs. In the present article, we review the molecular identity, functional and structural characteristics of these pumps, mainly on the example of human erythrocytes, and discuss their physiological role in detoxification and in the multidrug resistance phenotype of cancer cells