Topoisomerase: An Overview

Abstract

The structure of DNA is a double-stranded helix, where the four bases are paired and stored in the center of this helix. The two strands of DNA are intertwined and this would require the two strands to be untwisted in order to access the information stored. Topoisomerases catalyze and guide the unknotting of DNA by creating transient breaks in the DNA using a conserved Tyrosine as the catalytic residue. Two classes of Topoisomerses are identified yet. Since the overall chemical composition and connectivity of the DNA does not change, the tangled and untangled DNAs are chemical isomers, differing only in their global topology, hence the enzymes are named as Topoisomerases. The insertion of viral DNA into chromosomes and other forms of recombination also require the action of topoisomerases. Topoisomerase inhibitors are agents designed to interfere with the action of topoisomerase enzymes, which control the changes in DNA structure by catalyzing the breaking and rejoining of the phosphodiester backbone of DNA strands during the normal cell cycle. Thus they are found to be important tools for treatment of cancer.