Topoisomerase I and II Activity Assays.

Area of Science:

• Biochemistry
• Molecular Biology
• Enzymology

Background:

• DNA topoisomerases (top1 and top2) are essential enzymes involved in vital cellular processes like DNA replication, transcription, and repair.
• These enzymes function by reversibly nicking DNA, a reaction involving a transesterification mechanism where a DNA phosphodiester bond is transferred to an enzyme's tyrosine residue.

Purpose of the Study:

• To elucidate the distinct mechanisms of action between eukaryotic DNA topoisomerase I (top1) and topoisomerase II (top2).
• To highlight the structural and functional differences in how top1 and top2 interact with DNA during their catalytic cycles.

Main Methods:

• Comparative analysis of the enzymatic mechanisms of top1 and top2.
• Review of established literature detailing topoisomerase function and structure.

Main Results:

• Topoisomerase I (top1) functions as a monomer, catalyzing a single-strand break and covalently binding to the 3'-terminus, leaving a 5'-hydroxyl end.
• Topoisomerase II (top2) functions as a homodimer, typically creating a double-strand break with a four-base overhang, covalently binding to the 5'-terminus, and leaving a 3'-hydroxyl end.
• Top1 activity does not require an energy cofactor, whereas top2 hydrolyzes adenosine triphosphate (ATP) during its catalytic cycle.

Conclusions:

• Eukaryotic top1 and top2 enzymes exhibit significant differences in their mechanisms of action, monomeric vs. dimeric states, and DNA cleavage patterns.
• Understanding these distinctions is fundamental to comprehending DNA topology regulation in cellular processes.