DnaB helicase activity is modulated by DNA geometry and force

Area of Science:

• Molecular Biology
• Biophysics
• Biochemistry

Background:

• DnaB is the essential replicative helicase in Escherichia coli, a hexameric motor protein.
• It encircles single-stranded DNA (ssDNA) and unwinds double-stranded DNA (dsDNA).
• The precise microscopic mechanisms and regulatory flexibility of DnaB remain largely unknown.

Purpose of the Study:

• To investigate the translocation and unwinding mechanisms of single DnaB molecules.
• To understand how mechanical force and DNA geometry influence DnaB activity.
• To explore the factors modulating DnaB's function during DNA replication.

Main Methods:

• Quantification of single DnaB molecule translocation and unwinding.
• Utilized three tethered DNA geometries under controlled tension.
• Applied varying forces to DNA substrates to study mechanical effects.

Main Results:

• DnaB unwinding is significantly enhanced by force-induced destabilization of dsDNA.
• The degree of force-induced enhancement varies with DNA tension geometry.
• DnaB activity exhibits force- and geometry-dependent pauses.
• Helicase translocation speed decreases under high tension on the bound strand.

Conclusions:

• Force plays a crucial role in modulating DnaB unwinding efficiency.
• DNA geometry and applied tension influence DnaB's pausing behavior and translocation dynamics.
• DnaB performs mechanical work against applied forces during translocation.
• Results provide insights into DnaB's molecular mechanisms and regulatory strategies.