Ribbon Diagram Of Human Thymidylate Synthetase

However, the majority of known anti-cancer drugs target normal cells as well. Methotrexate, formerly known as amethopterin, is an antimetabolite used in the treatment of some forms of cancer (Shacter and Law, 1956). It inhibits the function of dihydrofolate reductase (DHFR) by tightly binding to the enzyme. Following this slow interaction between methotrexate and DHFR, an enzyme-NADPH-inhibitor complex is formed (Stone et al., 1984). Therein, DHFR is rendered unable to catalyze the NADPH-dependent reduction of dihydrofolate to tetrahydrofolate (Anderson, 2017). Tetrahydrofolate is an important methyl group shuttle in the de novo synthesis of purine and pyrimidine nucleotides and some amino acids (Barbara and Hiroshi, 2002). Therefore, eliminating it from cells is a good therapeutic strategy against cancer cells, as it would limit the de novo synthesis of purines and pyrimidines (Lane and Fan, 2015). Inhibiting the function of DHFR by its competitive inhibitor methotrexate is one such good therapeutic strategy, as it would disable DHFR from converting dihydrofolate into tetrahydrofolate. However, some types of cancer cells had acquired some forms of resistance against methotrexate (Hans et al., 2011). Equally important, methotrexate should be administered in well established low doses, because it affects

In order to enter the mitochondria, fatty acids are oxidised to fatty acyl-coA. The breakdown of ATP to AMP and pyrophosphate provides energy for this process. Moreover, fatty acyl-coA cannot pass through the inner mitochondrial membrane. Hence, the enzyme carnitine acyl transferase I replaces the coA with carnitine and then fatty acyl-carnitine passes through the acyl-carnitine I carnitine transporter into the mitochondrial matrix. In the matrix, fatty acyl-coA is regenerated by carnitine acyltransferase II. This allows beta oxidation to occur where fatty acid chains split into several molecules of acetyl-coA, yielding one NADH and one FADH2. This process involves the removal of two carbons from the carboxyl chain leading to a fatty acyl-coA chain two carbons shorter through four reactions. In reaction 1, oxidation dehydrogenation occurs converting fatty acyl-coA to trans-Δ2-enoyl-coA. This is catalyzed by the enzyme acyl-coA-dehydrogenase and electrons are transferred to FAD , reducing it to FADH2. Reaction 2 is catalyzed by enoyl-coA-hydratase, where trans-Δ2-enoyl-coA is hydrated to L-β-hydroxyl-acyl-coA. Reaction 3 is catalysed by β-hydroxyl-coA dehydrogenase, where two electrons are transferred fo NAD+ to form NADH, and β ketoacyl-coA is formed. In reaction 4, thiolytic cleavage causes the two carbons at the

The chemical Structures of thymidine and AZT are identical with the exception of the terminal group. If viral reverse transcriptase takes up AZT and places it into the growing DNA strand, transcription ceases as a new bond cannot be formed to the next base pair in the growing chain. Further, AZT is selectively picked up by retroviral reverse transcriptase while normal cells prefer thymidine for transcription so toxicity is limited for AZT(Furman 1985)

The thyroid stimulating hormone receptors are G-protein linked and are found extracellularly in the thyroid glands. When activated, synthesis of hormonally active iodothyronines T3 (triiodothyronine) and T4 (thyroxine) begins (Park and Chatterjee, 2005). This process begins with iodide is transported into the thyroid gland by the sodium iodide symporter found in the membrane of thyroid follicular cells (Park and Chatterjee, 2005). The iodotyrosine residues monoiodotyrosine and diiodotyrosine are then formed through iodine organification where the iodide is oxidised using hydrogen peroxide and then bound to tyrosine in the thyroglobulin (Park and Chatterjee, 2005). The residues then bind together to form the hormonally active iodothyronines aforementioned (Park and Chatterjee, 2005). Many catalytic enzymes mediate this process and are needed to ensure proper thyroid hormone synthesis. Failure in any steps of the synthesis process leads dyshormonogenesis and could be the result of genetic defects. Adequate synthesis of active thyroid hormone is necessary for the regulation of many developmental processes (Richter, C. et al.,

Methotrexate is an antimetabolite of folic acid that blocks the formation of thymine within the cell, rendering it incapable of DNA replication. As a chemotherapeutic agent, it is also employed as an alternative treatment for psoriasis and rheumatoid arthritis when they are unresponsive to conventional therapies. Methotrexate (MTX) induces an effect similar to 5-fluorouracil (5-FU) by interrupting the formation of thymine within the cell, which leads to the inability to replicate DNA. Unlike 5-FU, which inhibits the action of thymidylate synthetase, MTX binds tightly to dihydrofolate reductase (DHFR) and blocks the formation of tetrahydrofolate, leading to the depletion of associated folate co-factors (126).

Studies have shown that hydroxyl radical is responsible for oxidative DNA damage. Hydroxyl radicals come from the reaction between ascorbate (vitamin C), uranyl acetate, and hydrogen peroxide as illustrated in scheme 1 . The mechanism of DNA damage begins when the reaction between uranyl acetate and ascorbate (vitamin C) makes plasmid relaxation in pBluescript DNA. pBluescript DNA is a phagemid which includes many advantageous sequences for utilizing cloning with bacteriophage. The rate of DNA strand breaks multiply when the reaction between ascorbate (vitamin C), and uranyl acetate increase. In addition, hydrogen peroxide is the end product when there is a reaction between uranyl ion and ascorbate. DNA damage can happen

The function of this enzyme is to convert HMG-CoA into L-mevalonate. This conversion is the rate-limiting step in the production of cholesterol, shown in figure 1. This occurs mainly in the liver.

As I mentioned earlier, mutations in your NER or more specifically your GG-NER is responsible for genetics diseases such as XP. This disease is mostly linked with the inability to repair cells that contain photoproducts in your DNA that is initiated by UV light. These photoproducts include the (5–5) and (6–6) cyclobutane pyrimidine dimers (CPDs) and the (6–4) pyrimidine pyrimidinone dimers (PDs) that can involve T and C pyrimidines [7]. As these DNA are not repaired due to the lack of NER proteins, a mutation will occur which will substitute a Cytosine base to a Thymine base, it is most common when there are two Cytosine bases next to each other where it will go from CC to TT. This is very commonly found in protein p53. Patients with XP-C

Hydroxyl radical, product of the Fenton reaction, the most destructive species among oxygen radicals, is highly toxic and capable of attacking DNA, and oxidizing guanine bases resulting in the formation of mutagenic 8-hydroxy-2 '-deoxyguanosine (8-oxo-2dG) lesions. Among the purine and pyrimidine bases of DNA, guanine is the most sensitive base to oxidation. During an oxidative

Finally, 18F-FDG (4) is produced by base hydrolysis

Methotrexate (MTX), is an antifolate drug that was first developed to treat certain types of cancer. The use in cancer therapy is at higher doses whereas its use in rheumatic diseases is at much lower doses. It was found that the addition of a maintenance therapy following remission comprising of 6 mercaptopurine daily along with methotrexate weekly resulted in higher chances of remission. As per the current ALL protocols, induction and consolidation therapy is followed by oral 6 MP/ methotrexate maintenance therapy is given until 2 to 3 years from diagnosis. The enzyme dihydrofolic acid reductase (DHFR), which acts by reducing dihydrofolates to tetrahydrofolates, is inhibited by methotrexate. The tetrahydrofolates that are formed by means of this enzyme are used in the synthesis of purine nucleotides and thymidylate as one - carbon carriers. Methotrexate, therefore, interrupts DNA synthesis, and interferes with its repair

Epigenetic modifications on histones and DNA exercise precise regulation of gene expression, and thus have a profound influence on cellular differentiation and function. The most widely studied modification on DNA is 5 methylcytosine (5mC) that frequently occurs in a CpG dinucleotide context. Initially, the de novo DNA methyltransferase (Dnmt) enzymes Dnmt3a and 3b mediate the transfer of the methyl group to cytosine, while the maintenance Dnmt1 ensures subsequent propagation of this mark through cell replication cycles. Because of prominent roles in gene repression, retro element silencing, X chromosome inactivation and gene imprinting, 5mC was initially thought to be irreversible. Thanks to burgeoning evidence, it is now clear that the methylcytosine can be removed through a number of mechanisms. Passive demethylation is proposed to remove 5mC over several cell replication cycles, through exclusion of the maintenance machinery from the replication fork. Active demethylation on the other hand constitutes removal of 5mC through enzymatic hydrolysis. The discovery of Ten Eleven Transclocation (TET) dioxygenase proteins was revolutionary. The TET proteins catalyze hydroxylation of 5mC to 5hmC, and conversion of 5hmC to 5-carboxylcytosine and finally to 5 formylcytosine. These 5mC derivatives enter the base excision repair pathway (BER), resulting in replacement of the methylcytosine with an unmodified cytosine. Second, although the role of deaminases is debated, these enzymes

In the critical experiment for this grant proposal, we observed that DJ-1-Cys-106-SO3- (Figs. 3, 4; Table 1) contributes to DJ-1 translocation to mitochondria (Fig. 9). Interestingly, we found that first, NHEJ-1 is also shifted to these organelles and second, it interacts with DJ-1 in mitochondria (Fig. 7). We hypothesize that posttranslational modifications of DJ-1 lead to its interaction with NHEJ-1 in these organelles. This may result in the impairment of mtDNA damage repair. To further study the mechanism of this interaction, we will use tandem mass spectrometry (QTOF, letter attached, Fig. 8) as a suitable method for enabling site mapping and quantification of chemical modifications of proteins. We will treat A549 cells with mt-OX as

3A). However, other nucleotides like deoxycytidine (Fig. 3A) are glycated at high α-oxoaldehyde concentrations forming 5-glycolylcytidine (Frischmann, M. et al 2005; Kasai, H. et al 1998; Krymkiewicz, N. 1993). Inter-strand cross-links in duplex DNA (Seidel W and Pischetsrieder M 1998; Kasai, H. et al 1998) and DNA–protein cross-links in human keratinocytes were reported at higher MG concentrations. A recent in vitro study has demonstrated that CEdG (Fig. 3B) formation in DNA can hinder the Klenow fragment-mediated DNA synthesis (Cao, H. et al 2007). Due to AGEs the hydrogen-bonding property of the modified guanine is affected, resulting efficient incorporation of purine than pyrimidine nucleotides (Cao, H. et al 2007). Addition of bulky AGEs groups on the N2 position of guanine altered the Watson–Crick base pairing characteristic of these nucleobases resulting in destabilization of duplex DNA. The presence of dGTP-AGEs in DNA may change DNA structure, leading to the formation of abasic sites and DNA strand breaks (Pischetsrieder, M. et al 1999; Seidel W and Pischetsrieder M 1998; Cao, H. et al 2007). DNA glycation generates several nucleotide adducts that increases oxidative stress by the generation of hydrogen peroxide, superoxide, and hydroxyl radicals (Mistry, M. et al 2003; Thornalley, P.J. 1996). Recently a study demonstrated an accumulation of

The second stage of the process is complementary base pairing. In this stage, new complementary nucleotides are positioned following the rules of complementary base pairing: adenine (A) to thymine (T) and guanine (G) to cytosine (C). Then, the binding of free nucleotide with complementary bases is catalyzed by DNA polymerase.