Topoisomerase IV

Topoisomerase IV is one of two type-II topoisomerases in bacteria, the other being DNA gyrase. Like gyrase, topoisomerase IV is able to pass one double-strand of DNA through another double-strand of DNA, thereby changing the linking number of DNA by two in each enzymatic step.

Functions

Topoisomerase IV has two functions in the cell.

First, it is responsible for unlinking, or decatenating, DNA following DNA replication. The double-helical nature of DNA and its semiconservative mode of replication causes the two newly replicated DNA strands to be interlinked. These links must be removed in order for the chromosome (and plasmids) to segregate into daughter cells so that cell division can complete.
Topoisomerase IV's second function in the cell is to relax positive supercoils. It shares this role with DNA gyrase, which is also able to relax positive supercoils. Together, gyrase and topoisomerase IV remove the positive supercoils that accumulate ahead of a translocating DNA polymerase, allowing DNA replication to continue unhindered by topological strain.
DNA gyrases are analogous enzymes in other organisms.

While topoisomerase IV does relax positive supercoils like DNA gyrase, it does not introduce further negative supercoiling like the latter enzyme.^[1]

Clinical significance

Topoisomerase IV is also a target of antibiotics, such as the quinolone drugs, which include ciprofloxacin.

References

↑ Kato, Jun-ichi; Suzuki, Hideho; Ikeda, Hideo (25 December 1992). "Purification and characterization of DNA topoisomerase IV in Escherichia coli". Journal of Biological Chemistry. 267 (36): 25676–25684. PMID 1334483.

External links

Wikimedia Commons has media related to DNA topoisomerase IV.

DNA Topoisomerase IV at the US National Library of Medicine Medical Subject Headings (MeSH)

Isomerase: topoisomerases (EC 5.99)

5.99.1	Type I topoisomerase Type II topoisomerase gyrase topoisomerase IV

Enzymes

Activity	Active site Binding site Catalytic triad Oxyanion hole Enzyme promiscuity Catalytically perfect enzyme Coenzyme Cofactor Enzyme catalysis Enzyme kinetics Lineweaver–Burk plot Michaelis–Menten kinetics

Regulation	Allosteric regulation Cooperativity Enzyme inhibitor

Classification	EC number Enzyme superfamily Enzyme family List of enzymes

Types	EC1 Oxidoreductases (list) EC2 Transferases (list) EC3 Hydrolases (list) EC4 Lyases (list) EC5 Isomerases (list) EC6 Ligases (list)

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