Topoisomerase II

Topoisomerase II (or Topo II) is an enzyme that modulates the topological states of DNA during DNA replication. It is part of the topoisomerase family of enzymes, which control and modify the topologic states of DNA. Topoisomerase II is further divided into two isoforms: Topoisomerase II alpha and Topoisomerase II beta.

Function

Topoisomerase II plays a crucial role in DNA replication, transcription, chromosome condensation, and chromosome segregation. It introduces double-strand breaks into DNA, which allows the DNA to be untangled and the strands to be separated. This is particularly important during DNA replication, as the DNA helix must be unwound to allow the replication machinery to access the genetic material.

Structure

Topoisomerase II is a homodimeric enzyme, meaning it is composed of two identical subunits. Each subunit consists of four domains: an ATPase domain, a DNA binding domain, a breakage-reunion domain, and a C-terminal domain. The ATPase domain is responsible for hydrolyzing ATP, the DNA binding domain binds to the DNA, the breakage-reunion domain introduces the double-strand breaks and reseals them, and the C-terminal domain is involved in protein-protein interactions.

Clinical significance

Topoisomerase II is a target for several anticancer drugs, including etoposide, doxorubicin, and mitoxantrone. These drugs work by stabilizing the intermediate complex that forms when topoisomerase II introduces a double-strand break into the DNA, preventing the enzyme from resealing the break and leading to DNA damage and cell death.

See also

• Topoisomerase
• Topoisomerase II alpha
• Topoisomerase II beta
• DNA replication
• Anticancer drugs

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