What is the Difference Between DNA Gyrase and Topoisomerase

The main difference between DNA gyrase and topoisomerase is that DNA gyrase is a class of topoisomerase that catalyzes the ATP-dependent negative supercoiling of double-stranded closed-circular DNA, whereas topoisomerase is an enzyme that controls the topological transition of DNA. 

DNA gyrase and topoisomerase are two enzymes that reduce the topological strain in an ATP-dependent manner.     

Key Areas Covered

1. What are DNA Gyrase
– Definition, Structure, Function
2. What is Topoisomerase
– Definition, Types, Function
3. Similarities Between DNA Gyrase and Topoisomerase
– Outline of Common Features
4. Difference Between DNA Gyrase and Topoisomerase
– Comparison of Key Differences

Key Terms 

DNA Gyrase, Topoisomerase

What is DNA Gyrase

DNA gyrase is an essential enzyme that catalyzes the ATP-dependent negative supercoiling of double-stranded closed-circular DNA. It is a type II topoisomerase enzyme. The unwinding of double-stranded DNA occurs by elongating RNA polymerase or by helicase. It occurs in the progressing replication fork. DNA gyrase is actively involved in the negative supercoiling of DNA while relaxing positive supercoils. It loops the template to form a crossing, then cuts one of the double helices and passes the other through it before releasing the break. Also, it occurs in bacteria. Their DNA is single and circular. DNA gyrase cuts the DNA, and the two ends are twisted around each other to form a supercoil. 

Figure 1: DNA Gyrase Catalytic Cycle

Furthermore, DNA gyrase also occurs in the eukaryotic plastids. Also, it occurs in the apicoplast in the malarial parasites. Additionally, DNA gyrase is a tetrameric enzyme consisting of 2 GyrA (“A”) and 2 GyrB (“B”) subunits. It contains three pairs of gates that open and close sequentially. They allow the direct transfer of DNA segments, introducing negative supercoils. In the GyrB subunit, N gates occur that depend on ATP. The binding of 2 ATP molecules leads to the dimerization and closing of the N gate.  

What is Topoisomerase

Topoisomerase is a nuclear enzyme that plays a key role in DNA transcription, replication, recombination, and DNA segregation. Two major forms of topoisomerases occur in the cells. They are type I and type II topoisomerases. Importantly, the type I topoisomerase forms single-stranded cuts, while the type II topoisomerase forms double-stranded cuts. Meanwhile, type I topoisomerase contains two subtypes: IA and IB. The type IA topoisomerase is homologous to E. coli topoisomerase I. Also, the type IB topoisomerase is homologous to the human topoisomerase I.

Figure 2: Catalytic mechanisms of Topoisomerase

Moreover, the main function of topoisomerase is to alter the topological state of DNA. It relaxes supercoiled DNA. However, bacterial type II topoisomerase introduces negative supercoils to DNA. Topoisomerase is an important target for antibiotics and many chemotherapeutic agents. Anticancer agents can activate against eukaryotic topoisomerase. 

Similarities Between DNA Gyrase and Topoisomerase

• DNA gyrase and topoisomerase are two enzymes that reduce the topological strain in DNA.
• They depend on ATP.

Difference Between DNA Gyrase and Topoisomerase

Definition

DNA gyrase is a type II topoisomerase that introduces or removes negative supercoils and forms or resolves catenanes. In contrast, topoisomerase refers to any of a class of enzymes that reduce supercoiling in DNA by breaking and rejoining one or both strands of the DNA molecule.

Type

DNA gyrase is a topoisomerase type, while topoisomerase is a class of enzymes that removes topological strain in DNA.   

Classes 

DNA gyrase is a type II topoisomerase, while topoisomerase contains type I and type II. 

Function

DNA gyrase catalyzes the ATP-dependent negative supercoiling of double-stranded closed-circular DNA, while topoisomerase catalyzes changes in the topological state of DNA.

Conclusion

In brief, DNA gyrase and topoisomerase are two enzymes that catalyze topological changes in DNA. They are ATP-dependent. DNA gyrase is a type II topoisomerase that catalyzes ATP-dependent negative supercoiling of double-stranded, closed circular DNA. In comparison, the two types of topoisomerases are type I and type II. They catalyze the changes in the topological state of NDA. Therefore, the main difference between DNA gyrase and topoisomerase is their function.

References:

1. Reece RJ, Maxwell A. DNA gyrase: structure and function. Crit Rev Biochem Mol Biol. 1991;26(3-4):335-75. doi: 10.3109/10409239109114072. PMID: 1657531.
2. Nitiss JL, Soans E, Rogojina A, Seth A, Mishina M. Topoisomerase assays. Curr Protoc Pharmacol. 2012 Jun;Chapter 3:Unit 3.3.. doi: 10.1002/0471141755.ph0303s57. PMID: 22684721; PMCID: PMC3397423.

Image Courtesy:

1. “Gyrase catalytic cycle eng Sutormin eng” By Monochamus Sutor – Own work (CC-BY SA 4.0) via Commons Wikimedia
2. “Catalytic mechanisms of Topoisomerases” By Kcneuman – Own Work (CC-BY SA 4.0) via Commons Wikimedia