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DNA Topoisomerases

DNA Topoisomerases

Topoisomerases are enzymes that relax overwound DNA molecules during various cell processes, including DNA replication and transcription. These enzymes regulate positive and negative DNA supercoiling without changing the nucleotide sequence. DNA overwinding in a clockwise direction results in positively supercoiled DNA, whereas underwinding in a counterclockwise direction produces negatively supercoiled DNA.
Types and Mechanism of action
Topoisomerases are divided into two main types. Type I...

DNA Helicases

DNA Helicases

DNA unwinding helicase enzymes are a type of motor protein. Motor proteins can translocate along filaments or polymers using energy generated from ATP hydrolysis. Helicases are involved in all the important cellular processes where DNA unwinding is required, such as DNA replication, repair, recombination, and transcription. They are present in all living organisms, but vary in their structure, function, and mechanism of action. For example, in prokaryotes, DnaB helicase binds and translocates...

Single-Strand DNA Binding Proteins

Single-Strand DNA Binding Proteins

For successful DNA replication, the unwinding of double-stranded DNA must be accompanied by stabilization and protection of the separated single strands of the DNA. This crucial task is performed by single-strand DNA-binding (SSB) proteins. They bind to the DNA in a sequence-independent manner, which means that the nitrogenous bases of the DNA need not be present in a specific order for binding of SSB proteins to it. The binding of SSB proteins straightens single-stranded DNA (ssDNA) and makes...

Inhibitors of Bacterial DNA Synthesis

Inhibitors of Bacterial DNA Synthesis

Bacterial pathogens depend on precise and efficient DNA replication to sustain infection. Two type II topoisomerases—DNA gyrase and topoisomerase IV—are critical to this process, as they resolve DNA supercoiling and unlink chromosomes during replication. Fluoroquinolones, synthetic derivatives of quinolones, exploit this mechanism by stabilizing the transient DNA–enzyme cleavage complex, preventing strand religation, and causing lethal double-strand breaks. These antibiotics are selectively...

The DNA Helix

The DNA Helix

The DNA Helix

The DNA Helix

Deoxyribonucleic acid, or DNA, is the genetic material responsible for passing traits from generation to generation in all organisms and most viruses. DNA is composed of two strands of nucleotides that wind around each other to form a spring-like structure called a double helix. However, the double helix is not perfectly symmetrical. Instead, there are regularly occurring grooves in the structure. The major groove occurs where the sugar-phosphate backbones are relatively far apart. This space...

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Related Experiment Video

Updated: Jul 12, 2026

Simple and Fast Rolling Circle Amplification-Based Detection of Topoisomerase 1 Activity in Crude Biological Samples

Simple and Fast Rolling Circle Amplification-Based Detection of Topoisomerase 1 Activity in Crude Biological Samples

Published on: December 2, 2022

Human DNA topoisomerase IB: structure and functions.

Erica Cretaio¹, Luca Pattarello, Yari Fontebasso

¹Department of Biology, University of Padova, Padova, Italy.

The Italian Journal of Biochemistry

|August 29, 2007

Summary

Human DNA Topoisomerase I, a crucial enzyme for DNA replication and transcription, is analyzed for its structure-function relationship. This review details its four domains and catalytic mechanism in DNA relaxation.

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Published on: November 10, 2016

Area of Science:

Biochemistry
Molecular Biology
Enzymology

Background:

Human DNA Topoisomerase I is a monomeric enzyme essential for DNA topology regulation.
It comprises four distinct domains: N-terminal, core, linker, and C-terminal, each with specific roles.
The enzyme's activity involves nicking and rejoining DNA strands to relax supercoiled DNA.

Purpose of the Study:

To review and analyze the structure-function relationship of Human DNA Topoisomerase I.
To elucidate how the enzyme's distinct domains contribute to its catalytic activity.
To highlight the enzyme's critical role in fundamental biological processes.

Main Methods:

Literature review of structural and functional studies on Human DNA Topoisomerase I.
Analysis of domain organization and their contribution to DNA binding and catalysis.
Correlation of structural features with enzyme activity in DNA relaxation.

Main Results:

The N-terminal domain mediates protein-protein interactions.
The core domain is crucial for DNA binding and stabilization during catalysis.
The C-terminal domain houses the active site responsible for nicking and rejoining DNA strands.
The linker domain plays a role in coordinating domain interactions.

Conclusions:

The multi-domain structure of Human DNA Topoisomerase I is intricately linked to its function in DNA topology management.
Understanding the structure-function relationship is key to comprehending its vital roles in DNA replication, transcription, and recombination.
This enzyme remains a significant target for therapeutic interventions.