The structural basis for substrate specificity in DNA topoisomerase IV

Area of Science:

• Molecular Biology
• Structural Biology
• Biochemistry

Background:

• Bacteria utilize two main type IIA topoisomerases: DNA gyrase and topoisomerase IV, crucial for chromosome integrity.
• DNA gyrase introduces negative supercoils, while topoisomerase IV primarily decatenates DNA and relaxes positive supercoils.

Purpose of the Study:

• To elucidate the structural basis for the distinct functions of topoisomerase IV compared to DNA gyrase.
• To understand how the C-terminal domain of ParC influences topoisomerase IV substrate specificity.

Main Methods:

• X-ray crystallography to determine the structure of the full-length Escherichia coli ParC dimer at 3.0 A resolution.
• Biochemical assays to investigate the role of the ParC C-terminal domain in enzyme activity.

Main Results:

• The N-terminal DNA binding region of ParC is similar to GyrA, but the ParC dimer exhibits a different overall conformation.
• The ParC C-terminal domain (CTD) is a degenerate form of the GyrA CTD and is positioned differently.
• Biochemical data indicate the ParC CTD dictates substrate specificity by capturing specific DNA crossover geometries.

Conclusions:

• Structural variations between topoisomerase IV and DNA gyrase explain their specialized roles in managing bacterial chromosome topology.
• The ParC CTD is key to topoisomerase IV's substrate specificity, highlighting mechanistic parallels and differences between these essential enzymes.
• These findings provide insight into the evolutionary adaptations of bacterial type IIA topoisomerases for diverse chromosomal control needs.