Type II DNA topoisomerase is an essential class of enzymes involved in the regulation and alteration of the topological state of DNA molecules. These enzymes play a crucial role in various cellular processes, including DNA replication, transcription, recombination, and chromosome condensation.
Type II DNA topoisomerases are characterized by the ability to manipulate the topology of DNA by introducing transient double-strand breaks. This enables them to relieve torsional strain and to control the supercoiling and knotting of DNA molecules. These enzymes are classified into two subtypes, type IIA and type IIB, based on their structural and mechanistic differences.
Type IIA topoisomerases, which include DNA gyrase and topoisomerase IV, actively modulate DNA supercoiling by introducing negative supercoils and decatenating DNA, respectively. They possess two ATP-binding domains that facilitate the ATP-dependent breaking and resealing of DNA strands.
On the other hand, type IIB topoisomerases, exemplified by eukaryotic topoisomerase VI, function primarily in DNA decatenation during mitosis and meiosis. In contrast to type IIA enzymes, type IIB topoisomerases do not require ATP hydrolysis for their catalytic activity and employ tyrosine residues to form a covalent phosphotyrosine intermediate with the DNA substrate.
Overall, the type II DNA topoisomerases are crucial for maintaining genomic stability and ensuring proper DNA function. Their ability to control the topological state of DNA makes them vital components of cellular processes that rely on the unwinding, separation, or manipulation of DNA molecules.
