DNA gyrase

Structure of DNA gyrase

DNA gyrase is a type II topoisomerase enzyme that plays a crucial role in DNA replication and transcription. It is found in bacteria and some archaea, and is responsible for introducing negative supercoils into DNA molecules. This process helps to relieve the torsional strain that builds up ahead of the replication fork or transcription bubble.

Structure

DNA gyrase is a tetrameric enzyme composed of two GyrA and two GyrB subunits. The GyrA subunit contains the DNA cleavage and rejoining activity, while the GyrB subunit possesses the ATPase activity required for the enzyme's function. The two subunits are connected by a flexible linker region, allowing for conformational changes during the catalytic cycle.

Mechanism of Action

DNA gyrase acts by introducing double-stranded breaks in the DNA molecule, allowing it to pass another segment of DNA through the break. This process involves the formation of a covalent intermediate between the enzyme and the DNA, known as a cleavage complex. The GyrA subunit cleaves one strand of the DNA, while the GyrB subunit passes the other strand through the break. Finally, the DNA is resealed, and the enzyme is released.

Function

DNA gyrase is essential for the proper functioning of DNA replication and transcription in bacteria. By introducing negative supercoils, it helps to maintain the correct DNA topology and prevent the formation of DNA knots and tangles. It also plays a role in the regulation of gene expression by modulating the accessibility of DNA to other proteins involved in transcription and replication.

Clinical Significance

DNA gyrase is an important target for antibiotics, such as fluoroquinolones. These drugs inhibit the ATPase activity of the GyrB subunit, preventing the enzyme from functioning properly. By interfering with DNA gyrase, antibiotics can disrupt DNA replication and transcription, leading to bacterial cell death. This makes DNA gyrase an attractive target for the development of new antimicrobial agents.

See Also

• Topoisomerase
• DNA Replication
• Transcription (biology)