Type II topoisomerase
Enzyme that alters the supercoiling of double-stranded DNA
Type II topoisomerase is an enzyme that plays a crucial role in the manipulation of the topology of DNA. It is responsible for managing the supercoiling and entanglement of double-stranded DNA molecules during various cellular processes such as DNA replication, transcription, and chromosome segregation.
Function[edit | edit source]
Type II topoisomerases are essential for the maintenance of DNA topology. They function by creating transient double-strand breaks in the DNA molecule, allowing the passage of another segment of the double helix through the break, and then resealing the break. This mechanism is vital for resolving DNA supercoiling and catenation that occur during DNA replication and other cellular processes.
Mechanism[edit | edit source]
The enzyme operates by a "cut-and-pass" mechanism. It first binds to a segment of DNA, introduces a double-strand break, and then passes another segment of the DNA through this break before resealing it. This action requires the hydrolysis of ATP, which provides the necessary energy for the conformational changes in the enzyme.
Types[edit | edit source]
There are two main types of type II topoisomerases: DNA gyrase and topoisomerase IV. DNA gyrase is unique to bacteria and is responsible for introducing negative supercoils into DNA, which is crucial for DNA replication and transcription. Topoisomerase IV, also found in bacteria, primarily functions in the decatenation of replicated chromosomes.
Structure[edit | edit source]
Type II topoisomerases are typically composed of multiple subunits. The structure of these enzymes is complex, allowing them to perform their function of cutting and rejoining DNA strands. The enzyme's active site is responsible for the cleavage and re-ligation of DNA.
Inhibitors[edit | edit source]
Type II topoisomerases are targets for several antibiotics and anticancer drugs. Inhibitors such as quinolones and etoposide interfere with the enzyme's ability to manage DNA topology, leading to cell death. These inhibitors are used in the treatment of bacterial infections and cancer.
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