- DNA gyrase is an essential bacterial enzyme that introduces negative supercoiling into DNA, facilitating processes such as replication, transcription, and recombination. As a type II topoisomerase, it plays a crucial role in maintaining DNA topology and relieving supercoiling stress that arises during cellular functions.
- Found primarily in bacteria, DNA gyrase is a key target for antibiotic development, making it a significant enzyme in both molecular biology and medicine.
- DNA gyrase is a heterotetrameric enzyme composed of two GyrA and two GyrB subunits. The GyrA subunits contain the active site responsible for DNA cleavage and re-ligation, ensuring the breakage and rejoining of DNA strands. The GyrB subunits house the ATP-binding domain, which provides the energy required for supercoiling activity.
- The mechanism by which DNA gyrase functions involves a coordinated process of DNA strand passage. It creates a transient double-strand break, allowing another segment of DNA to pass through before rejoining the strands. This action introduces negative supercoiling, counteracting the natural tendency of DNA to become overwound during replication and transcription.
- DNA gyrase is indispensable for bacterial survival, as it regulates the supercoiling levels necessary for efficient cellular processes. Its primary function is to reduce topological stress in DNA, ensuring smooth progression of polymerases and preventing excessive DNA tangling.
- During replication, DNA gyrase works ahead of the replication fork to alleviate positive supercoiling generated by helicase activity. Without its function, the advancing replication machinery would stall due to accumulated torsional strain. Similarly, in transcription, gyrase ensures that RNA polymerase can move along the DNA template without encountering excessive supercoiling resistance.
- DNA gyrase operates using ATP hydrolysis to drive its strand-passage mechanism. The enzyme binds to a DNA segment, cleaves both strands, passes another segment through the gap, and then reseals the break. This action not only maintains genome integrity but also ensures efficient gene expression and cellular division.
- DNA gyrase is a vital target for antibiotics, particularly fluoroquinolones and aminocoumarins, which inhibit its activity and lead to bacterial cell death. Fluoroquinolones, such as ciprofloxacin, interfere with DNA gyrase by stabilizing the DNA-enzyme complex after cleavage, preventing re-ligation and causing lethal double-strand breaks. Aminocoumarins, like novobiocin, block the ATP-binding site, halting supercoiling function and disrupting bacterial replication.
- Beyond its role in antibacterial drug development, DNA gyrase is extensively studied in molecular biology for its impact on DNA structure and topology. Its ability to introduce negative supercoiling is crucial for experimental techniques such as plasmid manipulation and in vitro DNA transcription assays.
