Multimeric BLM is dissociated upon ATP hydrolysis and functions as monomers in resolving DNA structures.

Area of Science:

• Molecular Biology
• Genetics
• Biochemistry

Background:

• Bloom syndrome (BLM) is an autosomal recessive disorder linked to increased cancer risk.
• The oligomeric state of BLM protein during DNA unwinding has been unclear, despite evidence of a hexameric ring structure.

Purpose of the Study:

• To investigate the active form and kinetic mechanism of BLM in DNA unwinding.
• To clarify the role of BLM protein's oligomeric state in its helicase function.

Main Methods:

• Dynamic light scattering (DLS) was employed to assess BLM protein's size and oligomeric state.
• Stopped-flow assays were utilized to study the kinetics of BLM-mediated DNA unwinding.
• ATPase activity measurements were performed to analyze BLM helicase function.

Main Results:

• BLM protein multimers dissociated upon ATP hydrolysis.
• Kinetic studies demonstrated that BLM helicase functions as a monomer during duplex DNA unwinding across various conditions.
• BLM helicase likely functions as a monomer even when resolving complex DNA structures like Holliday junctions and D-loops.

Conclusions:

• BLM helicase unwinds DNA primarily as a monomer, not a multimer.
• This monomeric mechanism provides new insights into BLM's DNA unwinding process.
• Understanding BLM's function at a molecular level may illuminate the basis for Bloom syndrome phenotypes in carriers.