The Small Subunit of M · AquI Is Responsible for Sequence-Specific DNA Recognition and Binding in the Absence of the Catalytic Domain

AquI DNA methyltransferase (M · AquI) catalyzes the transfer of a methyl group from S-adenosyl-l-methionine to the C5 position of the outermost deoxycytidine base in the DNA sequence 5′-CCCGGG-3′. M · AquI is a heterodimer in which the polypeptide chain is separated at the junction between the two equivalent structural domains in the related enzyme M · HhaI. Recently, we reported the subcloning, overexpression, and purification of the subunits (α and β) of M · AquI separately. Here we describe the DNA binding properties of M · AquI. The results presented here indicate that the β subunit alone contains all of the information for sequence-specific DNA recognition and binding. The first step in the sequence-specific recognition of DNA by M · AquI involves the formation of binary complex with the target recognition domain in conjunction with conserved sequence motifs IX and X, found in all known C5 DNA methyltransferases, contained in the β subunit. The α subunit enhances the binding of the β subunit to DNA specifically and nonspecifically. It is likely that the addition of the α subunit to the β subunit stabilizes the conformation of the β subunit and thereby enhances its affinity for DNA indirectly. Addition of S-adenosyl-l-methionine and its analogues S-adenosyl-l-homocysteine and sinefungin enhances binding, but only in the presence of the α subunit. These compounds did not have any effect on DNA binding by the β subunit alone. Using a 30-mer oligodeoxynucleotide substrate containing 5-fluorodeoxycytidine (5-FdC), it was found that the β subunit alone did not form a covalent complex with its specific sequence in the absence or presence of S-adenosyl-l-methionine. However, the addition of the α subunit to the β subunit led to the formation of a covalent complex with specific DNA sequence containing 5-FdC

Association between the soluble epoxide hydrolase gene and preeclampsia

Objective: In this study the association between K55R polymorphism, methylation level of the EPHX2 promoter region, and PE was investigated in 520 individuals including 260 PE patients and 260 healthy pregnant women. Methods: K55R polymorphism and methylation level of the EPHX2 promoter were determined by the real-time PCR using double-dye hydrolysis probes and methylation-sensitive high-resolution melting analysis, respectively. Results: The presence of the K55R polymorphism was significantly higher in cases (28.1%) than controls (17.3%), and was associated with increased risk of PE (OR: 1.86; 95% CI: 1.09–2.63). Methylation levels of the EPHX2 promoter region in cases were significantly lower than controls. A 2.83 times increased PE risk was observed in pregnant women with EPHX2 promoter methylation levels of <25% (OR: 2.83; 95% CI: 1.15–6.91). Conclusion: In conclusion, hypomethylation of the promoter region of EPHX2 and K55R polymorphism were associated with significant increased risk of PE. sEH enzyme may play a role in the pathogenesis of PE by contributing to reduction of the vasodilatator, anti-hypertensive, and anti-inflammatory effects of EETs by rapid degradation of these molecules

Investigation of the Association between Genetic Polymorphism of Microsomal Epoxide Hydrolase and Primary Brain Tumor Incidence

mEH is a critical biotransformation enzyme that catalyzes the conversion of xenobiotic epoxide substrates into more polar diol metabolites: it is also capable of inactivating a large number of structurally different molecules. Two polymorphisms affecting enzyme activity have been described in the exon 3 and 4 of the mEH gene. The hypothesis of this study is that inherent genetic susceptibility to a primary brain tumor is associated with mEH gene polymorphisms. The polymorphisms of the mEH gene were determined with PCR-RFLP techniques and 255 Turkish individuals. Our results indicate that the frequency of the mEH exon 4 polymorphism (in controls) is significantly higher than that of primary brain tumor patients (OR = 1.8, 95% CI = 1.0–3.4). This report, however, failed to demonstrate a significant association between mEH exon 3 polymorphism and primary brain tumor susceptibility in this population. Analysis of patients by both histological types of primary brain tumor and gene variants showed no association, although analysis of family history of cancer between cases and controls showed a statistically significant association (χ2=7.0, P=0.01). Our results marginally support the hypothesis that genetic susceptibility to brain tumors may be associated with mEPHX gene polymorphisms

The role of two common FOXP3 gene promoter polymorphisms in preeclampsia in a Turkish population: a case–control study

Preeclampsia (PE), which occurs in approximately 5% of pregnancies worldwide and constitutes clinically serious complications in 2–3%, is one of the leading causes of maternal and prenatal morbidity and mortality. Recent studies report that regulatory T (Treg) cells, which act as immunosuppressant, are associated with PE. It is clearly defined that FOXP3/Scurfin (Forkhead Box P3) is involved in the development and function of Tregs. However, there are different conclusions regarding the relationship between PE and FOXP3 gene polymorphisms for different populations. For this reason, in this study we investigate the association between FOXP3 gene promoter region polymorphisms and PE in a Turkish population 500 PE patients and 500 healthy pregnant women. Blood samples taken from pregnant women were studied by PCR-RFLP method. As a result, rs2232365 polymorphism was significantly associated with disease (p < .0001) while no significant association was found between rs3761548 polymorphism and the disease (p = .17). Based on these results, it is though that FOXP3 rs2232365 polymorphism may be predisposed to PE development in terms of Turkish population. However, further and functional studies are needed in terms of other polymorphisms and mutations.IMPACT STATEMENT What is already known on this subject? A number of recent publications suggest that Tregs may play a role in the pathogenesis of PE. It is known that a stable and high FOXP3 expression is required to maintain the suppressive T cell function of Tregs. Down regulation of FOXP3 in PE has been reported in many previous studies, but the mechanism is still uncertain. What do the results of this study add? Our study has examined two FOXP3 promoter region polymorphisms in terms of Turkish population for the first time. Rs2232365 polymorphism associated with the disease in heterozygous genotype. What are the implications of these findings for clinical practice and/or further research? It has been shown that FOXP3 gene promoter region polymorphisms may be associated with PE for Turkish population. Our results can be a guide for more detailed statistical evaluations and functional studies

The DNA recognition subunit of a DNA methyltransferase is predominantly a molten globule in the absence of DNA

AbstractEnzyme-catalysed DNA methylation provides an opportunity for the modulation of protein-DNA recognition in biological systems. Recently we have demonstrated that the smaller of the two subunits of the heterodimeric, cytosine-specific DNA methyltransferase, M.AquI, is largely responsible for sequence-specific DNA recognition. Here we present evidence from a series of NMR, fluorescence and circular dichroism spectroscopy experiments that the DNA binding subunit of M.AquI has the characteristics of a molten globule in the absence of the catalytic machinery. In this metastable state this subunit retains its ability to bind DNA in a sequence-specific manner. We believe this finding offers an insight into the structural flexibility which underpins the mechansim of action of these enzymes, and may provide a possible biological role for molten globules in protein function