GSTA1 Human
Description
Structure and Functional Roles
Table 1: Functional Domains of GSTA1
| Domain | Function |
|---|---|
| N-terminal domain | Binds glutathione and stabilizes the thiol group during catalysis . |
| C-terminal domain | Substrate-binding pocket for electrophilic compounds (e.g., chemotherapeutics) . |
Genetic Diversity and Population Variability
Polymorphisms in the GSTA1 promoter region significantly alter enzyme expression and metabolic efficiency. A 2021 study analyzing 2,501 individuals identified six promoter SNPs (-52, -69, rs3957356, rs3957357, rs4715332, rs4715333) with distinct haplotype distributions across super-populations :
Table 2: GSTA1 Metabolic Phenotype Distribution
| Population | Fast Metabolizers (%) | Slow Metabolizers (%) |
|---|---|---|
| African | 46.9 | 9.6 |
| East Asian | 23.5 | 25.1 |
| European | 3.6 | 22.4 |
| South Asian | 13.1 | 32.9 |
| American | 6.4 | 12.0 |
SNPs at positions -52 and -69 had the strongest impact on transcriptional activity, with African populations harboring unique haplotypes (A1a, B2a, B2b) .
Cancer Progression and Drug Resistance
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Tumor suppression: Downregulation of GSTA1 in NSCLC A549 cells reduced proliferation by 40% and increased apoptosis by 2.5-fold .
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Chemotherapy resistance: Overexpression in cancer cells confers resistance to alkylating agents (e.g., busulfan, chlorambucil) by detoxifying reactive intermediates .
Table 3: GSTA1 Diplotype Effects on Busulfan Pharmacokinetics
| Diplotype Group | Metabolic Capacity | Clearance (ml/min/kg) | Dose Adjustment Ratio |
|---|---|---|---|
| Group I (e.g., A2A2) | Rapid | 3.8 ± 0.9 | 1.2 ± 0.3 |
| Group IV (e.g., B1aB1a) | Slow | 2.1 ± 0.7 | 0.9 ± 0.2 |
In pediatric hematopoietic stem cell transplantation, patients with rapid-metabolizer diplotypes required 20% higher busulfan doses to achieve therapeutic exposure .
Tissue-Specific Expression
GSTA1 is predominantly expressed in hepatocytes and renal proximal tubules, with moderate levels in the adrenal gland and gastrointestinal tract .
Therapeutic Targeting and Inhibitors
Recent studies highlight GSTA1 inhibitors (e.g., dichlorotriazine derivatives) as potential chemosensitizers to overcome drug resistance . These compounds irreversibly bind the substrate pocket, blocking detoxification of chemotherapeutic agents .
Future Directions
Research priorities include:
Product Specs
The specific activity, determined by measuring the conjugation of 1.0 µmole of 1-chloro-2,4-dinitrobenzene (CDNB) with reduced glutathione per minute at pH 6.5 and 25°C, is 35,000 pmol/min/µg.
Q&A
What is the GSTA1 gene and what is its primary function in human metabolism?
GSTA1 encodes a member of the glutathione S-transferase family that catalyzes the conjugation of glutathione to various electrophilic compounds. This enzyme plays a crucial role in the detoxification of carcinogens, therapeutic drugs, environmental toxins, and products of oxidative stress . It has a particular role in protecting cells from reactive oxygen species and peroxidation products . Additionally, GSTA1 is involved in hormone biosynthesis by catalyzing the isomerization of D5-androstene-3,17-dione (AD) into D4-androstene-3,17-dione . The enzyme also participates in the metabolism of oxidized linoleic acid through its glutathione-dependent peroxidase activity toward fatty acid hydroperoxides such as (13S)-hydroperoxy-(9Z,11E)-octadecadienoate .
What are the main substrates of GSTA1 enzyme in research settings?
Researchers utilize several key substrates to assess GSTA1 activity:
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Δ5-androstene-3,17-dione (AD): Used as a specific marker substrate for hGSTA1
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Cumene hydroperoxide (CuOOH): Used as a marker substrate for the hGSTA subfamily
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1-chloro-2,4-dinitrobenzene (CDNB): Used as a general marker substrate for hGST enzymes
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Prostaglandin A2 (PGA2) and prostaglandin J2 (PGJ2): GSTA1 catalyzes the formation of glutathione conjugates with these compounds
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(13S)-hydroperoxy-(9Z,11E)-octadecadienoate/13-HPODE: GSTA1 exhibits glutathione-dependent peroxidase activity toward this fatty acid hydroperoxide
These substrates provide valuable tools for assessing enzymatic activity in various experimental contexts.
What are the common haplotypes of GSTA1 and how do they vary across different populations?
GSTA1 haplotypes show significant variation across human populations. Based on six SNPs in the promoter region (-52, -69, -513, -567, -631, and -1142), several major haplotypes have been identified including *A1, *A2, *A3, *B1, *B1a, *B2, and others .
The distribution of these haplotypes varies significantly across the five super-populations identified in the 1000 Genomes Project:
In the Chinese population specifically, allele frequencies of hGSTA1A and hGSTA1B were found to be 87.1% and 12.9%, respectively, with genotype distributions of hGSTA1*A/A (75.0%), hGSTA1A/B (24.3%), and hGSTA1B/*B (0.7%) . This distribution pattern differs significantly from other racial populations.
Three new promoter haplotypes were discovered specifically in the African super-population, highlighting the greater genetic diversity in this group .
How do GSTA1 polymorphisms affect enzyme activity?
GSTA1 polymorphisms can significantly alter enzyme functionality. Studies have shown that variant forms of GSTA1 (such as hGSTA1B) demonstrate decreased activity compared to the wild type (hGSTA1A) .
In kinetic analyses of the variant hGSTA1:
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The Vmax value was reduced to 48% of the wild type
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The Km value was 62% of the wild type (p < 0.01)
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The catalytic efficiency (Vmax/Km) was consequently 76% of the wild type
What techniques are most effective for genotyping GSTA1 promoter haplotypes?
Several methodological approaches have proven effective for accurate GSTA1 genotyping:
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Polymerase Chain Reaction-Restriction Fragment Length Polymorphism (PCR-RFLP): This technique was successfully used to identify variants in the promoter region of the hGSTA1 gene in the Chinese population study .
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Computational haplotype inference: PHASE 2.1.1 software can be employed to infer haplotypes and diplotypes from genotype data of multiple SNPs, as demonstrated in the analysis of 2501 individuals from the 1000 Genomes Project .
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PCR-based differentiation of similar haplotypes: For closely related haplotypes like A1B1a and A3B2 that computational methods struggle to distinguish, specialized PCR-based approaches using specific primers have been developed:
These complementary approaches enable comprehensive and accurate determination of GSTA1 haplotypes in research settings.
What methodologies are most effective for assessing GSTA1 enzymatic activity in human liver samples?
For accurate assessment of GSTA1 enzymatic activity, researchers typically employ:
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Spectrophotometric assays: Using S-9 fractions from liver samples to measure enzymatic activity toward specific marker substrates .
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Substrate-specific activity measurements:
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Kinetic parameter determination: Analyzing reactions with various substrate concentrations to determine:
These methodologies provide a comprehensive profile of GSTA1 enzymatic properties and how they may be altered by genetic polymorphisms.
How do specific SNPs in the GSTA1 promoter region interact to influence gene expression?
The interaction between SNPs in the GSTA1 promoter creates complex patterns of gene expression regulation. Luciferase reporter assays (LRA) have revealed:
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SNPs at positions -52 and -69 have the most significant impact on GSTA1 expression, though other SNPs also contribute substantially to transcriptional activity .
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The influence of specific SNPs varies dramatically depending on haplotype context:
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In the *B haplotype context, changing T to G at a specific position increased expression 2.13-fold (p = 0.001)
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In the *A haplotype context, the A > G change decreased expression 2.15-fold (p = 0.005) in one sequence context (GCGTTC vs GCATTC) but increased expression 1.64-fold (p = 0.005) in another context (GCGTGG vs GCATGG)
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Some SNPs show minimal impact in certain contexts:
These findings have led researchers to propose a new model of cis-element interactions in the GSTA1 promoter that better explains the observed expression patterns .
What are the implications of GSTA1 polymorphisms for pharmacogenomic studies?
GSTA1 polymorphisms have significant pharmacogenomic implications:
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These polymorphisms directly influence the ability of individuals to metabolize different therapeutic drugs , potentially affecting both efficacy and toxicity.
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The significant variation in GSTA1 diplotype frequencies across populations necessitates population-specific approaches in drug development and personalized medicine .
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Researchers have developed metabolic categorization systems (fast, intermediate, and slow metabolizers) based on GSTA1 haplotypes to better predict drug metabolism phenotypes .
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The substantial individual variation in enzymatic activity even within populations carrying the same variant suggests that additional factors beyond genotype should be considered in pharmacogenomic analyses.
Due to these complexities, researchers recommend that future pharmacogenomic studies include comprehensive analysis of the complete GSTA1 promoter haplotype rather than focusing on isolated SNPs .
What challenges exist in correlating GSTA1 genotypes with metabolic phenotypes?
Several key challenges complicate the correlation between GSTA1 genotypes and metabolic phenotypes:
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Complex SNP interactions: The effect of individual SNPs on expression varies dramatically depending on the haplotype context, creating intricate patterns difficult to predict without functional studies .
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Population diversity: The significant differences in haplotype and diplotype frequencies across human populations make it challenging to generalize findings from one population to another .
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Individual variation: Substantial person-to-person differences in enzymatic activity exist even among individuals with identical GSTA1 variants .
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Haplotype discrimination difficulties: Some haplotypes (like A1B1a and A3B2) are challenging to distinguish without specialized genotyping methods, potentially leading to misclassification .
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Incomplete haplotype analysis: Many studies focus on only a subset of SNPs rather than comprehensive haplotype analysis, potentially missing important genetic determinants of phenotype .
To address these challenges, researchers recommend comprehensive haplotype analysis and functional validation through techniques like luciferase reporter assays to better understand and predict metabolic phenotypes .
How can GSTA1 genotype information be applied in clinical research?
GSTA1 genotyping offers several valuable applications in clinical research:
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Personalized dosing strategies: Knowing a patient's GSTA1 haplotype could guide dosage adjustments for drugs metabolized by this enzyme, potentially improving efficacy and reducing toxicity.
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Risk stratification: Since GSTA1 is involved in detoxifying carcinogens and environmental toxins , genotype information could help identify individuals at higher risk for certain conditions due to reduced detoxification capacity.
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Understanding population differences in drug response: The significant variation in GSTA1 haplotype frequencies across populations could help explain differential drug responses observed in multi-ethnic clinical trials.
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Biomarker development: GSTA1 haplotypes could serve as biomarkers for predicting metabolic phenotypes relevant to drug metabolism and toxicity response.
What are promising future research directions for GSTA1 human studies?
Several promising research directions could advance our understanding of GSTA1:
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Comprehensive phenotype mapping: Systematically correlating complete GSTA1 haplotypes with enzymatic activities toward a wide range of substrates to create more accurate metabolic prediction models.
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Environmental interaction studies: Investigating how environmental factors interact with GSTA1 polymorphisms to affect enzyme function, particularly for detoxification of environmental toxins and oxidative stress products .
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Systems biology approaches: Integrating GSTA1 genotype data with other detoxification enzyme polymorphisms to develop comprehensive models of xenobiotic metabolism.
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Structure-function analyses: Detailed studies of how promoter polymorphisms affect transcription factor binding and gene expression to better understand the molecular mechanisms underlying observed phenotypic differences.
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CRISPR-based functional validation: Using gene editing techniques to create isogenic cell lines with different GSTA1 haplotypes for precise assessment of functional differences.
These approaches could significantly advance our understanding of GSTA1's role in drug metabolism and detoxification processes, ultimately contributing to improved personalized medicine strategies.
Product Science Overview
Glutathione S-Transferase Alpha-1 (GSTA1) is a member of the glutathione S-transferase (GST) family of enzymes. These enzymes play a crucial role in the detoxification of a wide range of endogenous and exogenous compounds by catalyzing the conjugation of the tripeptide glutathione (GSH) to electrophilic centers on these compounds .
The GSTA1 gene is located on chromosome 6 in humans and is part of a cluster of similar genes and pseudogenes . The gene encodes a protein that is predominantly expressed in the liver and kidney, where it is involved in the detoxification processes . The protein structure of GSTA1 includes a conserved glutathione-binding site and a hydrophobic substrate-binding site, which are essential for its catalytic activity .
GSTA1 catalyzes the nucleophilic attack of the sulfur atom of glutathione on the electrophilic groups of a wide range of substrates, including carcinogens, therapeutic drugs, environmental toxins, and products of oxidative stress . This reaction is a critical step in the detoxification pathway, as it renders these compounds more water-soluble and thus easier to excrete from the body .
In addition to its role in detoxification, GSTA1 also exhibits glutathione peroxidase activity, which helps protect cells from reactive oxygen species and the products of lipid peroxidation . This activity is particularly important in protecting cells from oxidative damage and maintaining cellular homeostasis .
Polymorphisms in the GSTA1 gene can influence an individual’s ability to metabolize different drugs and detoxify various environmental toxins . These genetic variations can affect the efficacy and toxicity of certain medications, making GSTA1 an important factor in personalized medicine .
Increases in serum and urinary levels of GSTA1 have been associated with hepatocyte and renal proximal tubular necrosis, respectively . Therefore, GSTA1 can serve as a biomarker for monitoring liver and kidney injury .
