Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: EC:2.1.1.67 (thiopurine methyltransferase)
 551 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

In humans, the enzyme thiopurine methyltransferase (TPMT) metabolizes 6-thiopurine (6-TP) medications, commonly used for immune suppression and for the treatment of hematopoietic malignancies. Genetic polymorphisms in the TPMT protein sequence accelerate intracellular degradation of the enzyme through an ubiquitylation and proteasomal-dependent pathway. Research has led to the hypothesis that these polymorphisms destabilize the native structure of TPMT, resulting in the formation of misfolded or partially unfolded states, which are subsequently recognized for intracellular degradation. Addition of the cosubstrate, S-adenosylmethionine (SAM), prevents degradation of the TPMT polymorphs in experimental assays, presumably by stabilizing the native structure. Using a bacterial orthologue of TPMT from Pseudomonas syringae, we have used NMR spectroscopy to describe the consequences of binding sinefungin, a SAM analogue, on the structure and dynamics of the TPMT protein backbone. NMR chemical shift mapping experiments localize sinefungin to a highly conserved site in classical methyltransferases. Distal chemical shift changes involving the presumed active site cover imply indirect conformational changes induced by sinefungin, which may play a role in substrate recognition or the catalytic mechanism. Analysis of protein backbone dynamics based on NMR relaxation reveals a combination of complementary effects. Whereas the peripheral, inserted structural elements of the TPMT topology are conformationally stabilized by the presence of sinefungin, a consistent increase in backbone mobility is observed for the central, conserved structural elements. The potential implications for the structural and dynamic effects of binding sinefungin for the catalytic mechanism of the enzyme and the stabilization of the degradation-susceptible TPMT polymorphs are discussed.
Biochemistry 2004 Sep 28
PMID:Consequences of binding an S-adenosylmethionine analogue on the structure and dynamics of the thiopurine methyltransferase protein backbone. 1537 58

Iatrogenic malignancies represent a devastating and often fatal long-term effect of therapy administered for a prior condition, usually a primary cancer. Earlier diagnosis and the development of more effective cancer treatments over the last 30 years have considerably improved the long-term survival of patients. However, the burgeoning number of cancer survivors has led to a parallel increase in the number of cases of iatrogenic malignancy. Consequently, understanding host susceptibility factors, such that high-risk patients can be identified, has become a priority. However, this task is made difficult by the heterogeneity of iatrogenic malignancies. Nevertheless, the identification of polymorphic loci and pathways predicted to modify dose (e.g., glutathione S-transferases, nicotinamide adenine dinucleotide phosphate: quinone oxidoreductase, cytochrome P450, and thiopurine S-methyltransferase) or determine cellular outcome (e.g., nucleotide excision DNA repair, base excision DNA repair, DNA mismatch repair, and cell death signaling) after therapy has provided insight into how host genetics may impact on the risk of developing iatrogenic malignancy.
Pharmacogenomics 2005 Sep
PMID:Genetic susceptibility to iatrogenic malignancy. 1614 1

Thiopurine drugs are metabolized, in part, by S-methylation catalyzed by thiopurine S-methyltransferase (TPMT). Patients with very low or undetectable TPMT activity are at high risk of severe, potentially fatal hematopoietic toxicity when they are treated with standard doses of thiopurines. As human TPMT activity is controlled by a common genetic polymorphism, it is an excellent candidate for the clinical application of pharmacogenetics. Here, we report a new molecular approach developed to detect point mutations in the TPMT gene that cause the loss of TPMT activity. A fluorescently labeled amplified DNA is hybridized with oligonucleotide DNA probes immobilized in gel pads on a biochip. The specially designed TPMT biochip can recognize six point mutations in the TPMT gene and seven corresponding alleles associated with TPMT deficiency: TPMT*2; TPMT*3A, TPMT*3B, TPMT*3C, TPMT*3D, TPMT*7, and TPMT*8. The effectiveness of the protocol was tested by genotyping 58 samples of known genotype. The results showed 100% concordance between the biochip-based approach and the established PCR protocol. The genotyping procedure is fast, reliable and can be used for rapid screening of inactivating mutations in the TPMT gene. The study also provides the first data on the frequency of common TPMT variant alleles in the Russian population, based on a biochip analysis of 700 samples. TPMT gene mutations were identified in 44 subjects; genotype *1/*3A was most frequent.
Eur J Hum Genet 2006 Sep
PMID:Rapid genotyping of common deficient thiopurine S-methyltransferase alleles using the DNA-microchip technique. 1672 2

The genetic polymorphism of the thiopurine S-methyltransferase, TPMT, comprises at least 21 alleles causing three distinct drug metabolism phenotypes termed normal/high, intermediate, and deficient methylators. In consequence, adverse drug reactions may occur if standard doses of thiopurines are applied routinely. Genetic prediction of the methylator phenotype as a basis for dose selection requires the extensive knowledge of single nucleotide polymorphisms occurring naturally in the population. Here we describe three novel missense variants in the TPMT gene which were associated with an intermediate red blood cell TPMT activity in three Caucasians. The following alleles were designated: TPMT*20 (c.712A>G), *21 (c.205C>G), and *22 (c.488G>C). No further genetic variations in remaining coding regions as well as the 5'flanking region of TPMT were identified. These sequence variants are present in highly conserved nucleotide positions of the TPMT gene throughout various mammalian species and in zebra fish, and are predicted to be intolerant when the functional consequences of variations were analyzed using SIFT (Sorting Intolerant From Tolerant) algorithm. In Caucasians the occurrence of these genetic variants appears to be extremely rare since none of these alleles were identified in a randomly selected control population of 1048 individuals.
Hum Mutat 2006 Sep
PMID:Three novel thiopurine S-methyltransferase allelic variants (TPMT*20, *21, *22) - association with decreased enzyme function. 1691 10

The application of pharmacogenetics holds great promise for individualized therapy. However, it has little clinical reality at present, despite many claims. The main problem is that the evidence base supporting genetic testing before therapy is weak. The pharmacology of the drugs subject to inherited variability in metabolism is often complex. Few have simple or single pathways of elimination. Some have active metabolites or enantiomers with different activities and pathways of elimination. Drug dosing is likely to be influenced only if the aggregate molar activity of all active moieties at the site of action is predictably affected by genotype or phenotype. Variation in drug concentration must be significant enough to provide "signal" over and above normal variation, and there must be a genuine concentration-effect relationship. The therapeutic index of the drug will also influence test utility. After considering all of these factors, the benefits of prospective testing need to be weighed against the costs and against other endpoints of effect. It is not surprising that few drugs satisfy these requirements. Drugs (and enzymes) for which there is a reasonable evidence base supporting genotyping or phenotyping include suxamethonium/mivacurium (butyrylcholinesterase), and azathioprine/6-mercaptopurine (thiopurine methyltransferase). Drugs for which there is a potential case for prospective testing include warfarin (CYP2C9), perhexiline (CYP2D6), and perhaps the proton pump inhibitors (CYP2C19). No other drugs have an evidence base that is sufficient to justify prospective testing at present, although some warrant further evaluation. In this review we summarize the current evidence base for pharmacogenetics in relation to drug-metabolizing enzymes.
Pharmacol Rev 2006 Sep
PMID:Pharmacogenetics, drug-metabolizing enzymes, and clinical practice. 1696 50

The photostability of (E)-2-[3-(2-thioxopyrrolidin-3-ylidene)methyl]-tryptophan ((E)-TPMT), the main yellow pigment in salted radish, was studied. First we analyzed the photoproduct generated from (E)-TPMT under longwave UV irradiation. On the basis of NMR spectroscopy, the photoproduct was identified as Z-configurated TPMT, and isomerization from the Z- to the E-form was reversibly induced by Vis-light irradiation. The optimum wavelength for isomerization from the E- to the Z-form was 360-380 nm, and that for isomerization from the Z- to the E-form was 440-460 nm. The E/Z-ratios in the photostationary state under UV- and Vis-light irradiation conditions were approximately 0.95:1 and 26:1 respectively. The (Z)-isomer was more sensitive to light irradiation than the (E)-isomer in the quantum yield measurement. Yellowing was dependent on the ratio of the (Z)-isomer, because the b(*) and chroma value rose with increases in the (Z)-isomer by the colorimeters. Hence, it is possible that the formation of the (Z)-isomer contribute to the yellow color of takuan-zuke during long salting and fermentation.
Biosci Biotechnol Biochem 2008 Sep
PMID:Photoisomerization of 2-[3-(2-thioxopyrrolidin-3-ylidene)methyl]-tryptophan, a yellow pigment in salted radish roots. 1877 82

Human thiopurine S-methyltransferase (TPMT) is an essential protein in 6-mercaptopurine (6MP) drug metabolism. To understand the pharmacogenetics of TPMT and 6MP, X-ray co-crystal structures of TPMT complexes with S-adenosyl-L-methionine (AdoMet) and 6MP are required. However, the co-crystal structure of this complex has not been reported because 6MP is poorly water soluble. We used molecular dynamics (MD) simulation to predict the structure of the complex of human TPMT-AdoHcy(CH(2))6MP, where the sulfur atoms of AdoHcy and 6MP were linked by a CH(2) group. After 1300 picoseconds of MD simulation, the trajectory showed that 6MP was stabilized in the TPMT active site by formation of non-bonded interactions between 6MP and Phe40, Pro196 and Arg226 side chains of TPMT. The intersulfur distance between AdoHcy and 6MP as well as the binding modes and the interactions of our TPMT-AdoHcy model are consistent with those observed in the X-ray crystal structure of murine TPMT-AdoHcy-6MP complex. The predicted binding modes of AdoHcy and 6MP in our model are consistent with those observed in murine TPMT X-ray crystal structures, which provides structural insights into the interactions of TPMT, AdoHcy, and 6MP at the atomic level and may be used as a starting point for further study of thiopurine drug pharmacogenetics.
Bioinformation 2009 Sep 05
PMID:Molecular dynamics simulation of a human thiopurine S-methyltransferase complexed with 6-mercaptopurine model. 2019 69

The interindividual variation in the rate of drug metabolism and disposition has been known for many years. Pharmacogenomics dealing with heredity and response to drugs is a part of science that attempts to explain variability of drug responses and to search for the genetic basis of such variations or differences. Genetic polymorphisms of drug metabolizing enzymes and drug transporters have been found to play a significant role in the patients' responses to medication. Accumulating evidence demonstrates that certain nonsynonymous polymorphisms have great impacts on the protein stability and degradation, as well as the function of drug metabolizing enzymes and transporters. The aim of this review article is to address a new aspect of protein quality control in the endoplasmic reticulum and to present examples regarding the impact of nonsynonymous single-nucleotide polymorphisms on the protein stability of thiopurine S-methyltransferase as well as ATP-binding cassette (ABC) transporters including ABCC4, cystic fibrosis transmembrane conductance regulator (CFTR, ABCC7), ABCC11, and ABCG2. Furthermore, we will discuss the molecular mechanisms underlying posttranslational modifications (intramolecular and intermolecular disulfide bond formation and N-linked glycosylation) and ubiquitin-mediated proteasomal degradation of ABCG2, one of the major drug transporter proteins in humans.
J Pharm Sci 2011 Sep
PMID:Ubiquitin-mediated proteasomal degradation of ABC transporters: a new aspect of genetic polymorphisms and clinical impacts. 2156 8

Genetic polymorphisms of drug transporters as well as drug metabolizing enzymes have been documented to play a significant role in patients' responses to medication. A key requirement for advancing personalized medicine is the ability to rapidly and conveniently test for patients' genetic polymorphisms. We have recently developed a rapid and cost-effective method for single nucleotide polymorphism (SNP) detection, named Smart Amplification Process (SmartAmp), which enables us to detect genetic polymorphisms or mutations in 30 to 45 min under isothermal conditions without the need for DNA isolation and PCR amplification. This article presents the SmartAmp-based detection of SNPs in the thiopurine S-methyltransferase gene as well as in the ATP-binding cassette (ABC) transporter ABCC4 and ABCG2 genes that are critically involved in drug-induced adverse reactions. The SmartAmp method is expected to provide a practical and cost-effective tool for pharmacogenomics-based personalized medicine.
Curr Drug Metab 2012 Sep 01
PMID:The SmartAmp method: rapid detection of SNPs in thiopurine S-methyltransferase and ABC transporters ABCC4 and ABCG2. 2259 49

There are several hurdles to the clinical implementation of pharmacogenetics. One approach is to employ pre-prescription genotyping, involving interrogation of multiple pharmacogenetic variants using a high-throughput platform. We compared the performance of the Drug Metabolizing Enzymes and Transporters (DMET) Plus array (1,931 variants in 225 genes) with that of orthogonal genotyping methods in 220 pediatric patients. A total of 1,692 variants had call rates >98% and were in Hardy-Weinberg equilibrium. Of these, 259 were genotyped by at least one independent method, and a total of 19,942 single-nucleotide polymorphism (SNP)-patient sample pairs were evaluated. The concordance rate was 99.9%, with only 28 genotype discordances observed. For the genes deemed most likely to be clinically relevant (TPMT, CYP2D6, CYP2C19, CYP2C9, VKORC1, DPYD, UGT1A1, and SLCO1B1), a total of 3,799 SNP-patient sample pairs were evaluable and had a concordance rate of 99.96%. We conclude that the DMET Plus array performs well with primary patient samples, with the results in good concordance with those of several lower-throughput genotyping methods.
Clin Pharmacol Ther 2012 Sep
PMID:Concordance of DMET plus genotyping results with those of orthogonal genotyping methods. 2352 92


<< Previous 1 2 3 Next >>