Topoisomerase

• CAS Number: 80449-01-0
• CAS Number: 142805-56-9 (Type II)

Topoisomerases are enzymes that are responsible for changes in the topology of DNA molecules which are necessary for a supercoiling. There are two parent classes:

• Type I topoisomerases ( subclasses topoisomerase I & III)
• Type of the enzyme topoisomerase II corresponds gyrase in eukaryotes ( topoisomerases II and IV) in prokaryotes

Topoisomerase type I

Function of topoisomerase I in prokaryotes:

The bacterial topoisomerase I can relax only negative supercoiling. It requires magnesium ions for their activity. Prokaryotic topoisomerase I bind covalently by means of a Phosphotyrosinbindung to the 5 ' end of the strand break. This preserves the energy of the cleaved bond, and makes it possible to connect the both ends of the Topoisomerisierung again. For its activities, the enzyme does not require energy in the form of ATP.

Function of topoisomerase I in eukaryotes:

The eukaryotic topoisomerase I relaxes both positively and negatively supercoiled DNA. It binds by Phosphotyrosinbindung to the 3 ' end of the strand break.

By the time necessary for the processes of transcription and replication unwinding just read sections of DNA occurs in adjacent areas of the Helix automatically to positive supercoiling, a strong distortion of the DNA double helix, which is accompanied by torsional forces. To counteract the torsional forces the positive supercoiling is relaxed by eukaryotic topoisomerase type I. The topoisomerase type I causes a single-strand break without ATP to consume. At their departure from the DNA it closes the break again. Then remove the topoisomerase I & IV, the negative deviations of the Verwindungszustandes and thus represent the physiological normal state again.

Topoisomerase type II

Main article: type II topoisomerase

Function of topoisomerase II in prokaryotes:

The prokaryotic topoisomerase II causes negative supercoiling of DNA. Thus, it can relax positively supercoiled DNA and insert it into relaxed DNA negative twist. They induced to double-strand breaks; the negative supercoiling happens with ATP consumption.

Function of eukaryotic topoisomerase II alpha:

Eukaryotic topoisomerase II alpha can relax positive and negative supercoiling by means of double-strand break with ATP consumption.

Type II topoisomerases act on the one hand, contrary to the torsional forces above and influence the other hand, the spatial arrangement of DNA. They generate ATP consumption under a temporary DNA double- strand breakage, so that a fitting helix part can pass through the formed gap. This allows comprehensive Chromatinumordnungen.

Medical Relevance

Antibiotics from the family of gyrase inhibitors inhibit topoisomerase II and partially IV cytotoxic drugs such as irinotecan among the topoisomerase inhibitors.