Short-range translocation by a restriction enzyme motor triggers diffusion along DNA

Area of Science:

• Molecular Biology
• Biochemistry
• Enzymology

Background:

• Type III restriction-modification enzymes cleave bacteriophage DNA through long-range DNA site interactions.
• These interactions are mediated by one-dimensional diffusion, or 'DNA sliding', powered by ATP hydrolysis.
• A superfamily 2 helicase-like ATPase drives this process, but its precise roles remain incompletely understood.

Purpose of the Study:

• To investigate the multifaceted roles of ATP hydrolysis by the helicase-like domain in Type III enzyme function.
• To elucidate the mechanism of DNA sliding and long-range communication between DNA sites.

Main Methods:

• Ultrafast twist measurements using plasmonic DNA origami nano-rotors.
• Stopped-flow fluorescence assays.
• Gel-based assays to analyze DNA interactions and enzyme activity.

Main Results:

• The helicase-like domain stabilizes initial DNA binding with methyltransferase subunits.
• ATP hydrolysis induces environmental changes in adenine bases and remodels nucleoprotein complexes.
• Constrained translocation of a DNA loop (5-22 bp) is mediated by the helicase domain.
• DNA sliding initiation requires 8-15 bp downstream of the motor, aligning with nuclease domain binding.

Conclusions:

• The helicase-like ATPase domain plays multiple critical roles beyond simple DNA translocation.
• This study unifies previous, often contradictory, models of communication within Type III restriction-modification enzyme systems.
• The findings provide a comprehensive mechanistic understanding of how these enzymes achieve long-range DNA targeting.