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Genes and Genomics
Published in Firdos Alam Khan, Biotechnology Fundamentals, 2020
Topoisomerases are enzymes with both nuclease and ligase activity. These proteins change the amount of supercoiling in DNA and some of these enzymes work by cutting the DNA helix and allowing one section to rotate, thereby reducing its level of supercoiling; the enzymes then seal the DNA break. Other types of enzymes can cut one DNA helix and then pass a second strand of DNA through this break before rejoining the helix. Topoisomerases are required for many processes involving DNA, such as DNA replication and transcription. Helicases are proteins that are a type of molecular motor. They use the chemical energy in nucleoside triphosphates, predominantly ATP, to break hydrogen bonds between bases and unwind the DNA double helix into single strands. These enzymes are essential for most processes where enzymes need to access the DNA bases.
Genes and genomics
Published in Firdos Alam Khan, Biotechnology Fundamentals, 2018
Topoisomerases are enzymes with both nuclease and ligase activity. These proteins change the amount of supercoiling in DNA and some of these enzymes work by cutting the DNA helix and allowing one section to rotate, thereby reducing its level of supercoiling; the enzymes then seal the DNA break. Other types of enzymes are capable of cutting one DNA helix and then passing a second strand of DNA through this break, before rejoining the helix. Topoisomerases are required for many processes involving DNA, such as DNA replication and transcription. Helicases are proteins that are a type of molecular motor. They use the chemical energy in nucleoside triphosphates, predominantly ATP, to break hydrogen bonds between bases and unwind the DNA double helix into single strands. These enzymes are essential for most processes where enzymes need to access the DNA bases.
Glossary of scientific and technical terms in bioengineering and biological engineering
Published in Megh R. Goyal, Scientific and Technical Terms in Bioengineering and Biological Engineering, 2018
Topo-isomerase is an enzyme that regulates the overwinding or underwinding of DNA. The winding problem of DNA arises due to the intertwined nature of its double-helical structure. For example, during DNA replication, DNA becomes overwound ahead of a replication fork. If left unabated, this tension would eventually halt DNA replication. (A similar event happens during transcription.) In order to help overcome these types of topological problems caused by the double helix, topoisomerases bind to either single-stranded or double-stranded DNA and cut the phosphate backbone of the DNA. This intermediate break allows the DNA to be untangled or unwound, and, at the end of these processes, the DNA backbone is resealed again. Since the overall chemical composition and connectivity of the DNA do not change, the tangled and untangled DNAs are chemical isomers, differing only in their global topology, thus their name. Topoisomerases are isomerase enzymes that act on the topology of DNA.
Pharmacological properties of dicyanidoaurate(I)-based complexes: characterization and single crystal X-ray analysis
Published in Journal of Coordination Chemistry, 2019
Ahmet Karadağ, Ali Aydin, Şaban Tekin, Hüseyin Akbaş, Süreyya Dede
To investigate possible mechanisms of action in the test compounds, a human topoisomerase I assay was used in vitro. The human topoisomerase I, a nuclear enzyme that controls the topological state of DNA, is a significant aspect of approved anticancer medications, currently. The results obtained from lanes 5 to 7 show that none of the test compounds suppressed the activity of the human topoisomerase I as well as that of a camptothecin (Supplementary information Figure S8). These data, therefore, demonstrate that the compounds block cell proliferation in another way without using the suppression of human topoisomerase I activity in replication. In contrast, a similar study showed that gold complexes containing ligands with different properties and exhibiting different spatial locations arrest cell proliferation through suppression of human topoisomerase I activity in replication. For example, a square-planar gold complex, AuCl2(HL4), acts like both the topoisomerase IIα (Top2) and the topoisomerase IB (Top1) poisons in cell division [51]. A similar topoisomerase study performed by Yan and co-workers [17] revealed that cyclometalated Au(III) complexes [Au(C^N^C)(1,3-dimethylimidazol-2-ylidene)]CF3SO3 have anticancer properties by blocking topoisomerase I activity in vitro.
Camptothecin prodrug nanomicelle based on a boronate ester-linked diblock copolymer as the carrier of doxorubicin with enhanced cellular uptake
Published in Journal of Biomaterials Science, Polymer Edition, 2018
Ya Gao, Yi Xiao, Shiyuan Liu, Jiahui Yu
Camptothecin (CPT), isolated originally from Camptotheca acuminate, first identified in the mid-60s by Wall and Wani [30] has promising anticancer effects. It can inhibit topoisomerase I to induce apoptosis in rapidly dividing tumor cells [31,32]. Unfortunately, the drug has been prevented from being approved due to its poor solubility and unpredictable side effects [33]. It has been confirmed that the severe toxicity of CPT mainly results from its carboxylate form [34]. As well known, CPT exists in two forms depending on pH values [35]. The first one is closed lactone ring (E-ring) form at pH below 5, which is essential to the treatment of cancer. The second one is ring-open carboxylate form at basic pH. The 20-OH of E-ring can accelerate hydrolysis of CPT, resulting in ring opening at physiological pH. At the same time, human serum albumin can bind preferentially with the carboxylate form, which will result in the lactone ring opening more rapidly [36,37]. However, it has been found that modifying CPT at the 20 position as ester to construct prodrugs of CPT stabilizes the active lactone ring under physiological conditions [38]. Nowadays, CPT has been conjugated to a variety of polymers to form macromolecule polymer prodrugs of CPT, such as polyethylene glycol [39,40], dextran [41] and poly (L-glutamic acid) [42].
Synthesis, crystal structures and anti-cancer mechanism of Cu(II) complex derived from 2-acetylpyrazine thiosemicarbazone
Published in Journal of Coordination Chemistry, 2022
Yunyun Zheng, Bin Li, Yu Ai, Mengyao Chen, Xinhua Zheng, Jinxu Qi
Topoisomerase cuts the phosphodiester bond in one or two DNA strands and then rewinds and seals the strands to correct the length of the DNA chain [53]. It affects the catalysis of DNA strand splitting and binding and controls the DNA topological state [25]. Figure 6 demonstrates that topoisomerase I catalyzes the superhelical DNA to transform it into a relaxed state. When exposed to 100 μM of agents, the activity of Topo-I was significantly inhibited by L4, and 4a showed poor inhibitory activity. The accumulation of DNA supercoils is because of the inhibitory effect of 4a on Topo-I; this super-winding of DNA can inhibit the advancement of the DNA polymerase and may also prevent or destroy replication, resulting in cell death.