Assembly of a double hexameric helicase

Area of Science:

• Molecular Biology
• Virology
• Biochemistry

Background:

• Viral initiators are crucial for DNA replication, performing functions like origin binding, DNA melting, and unwinding.
• The papillomavirus E1 initiator forms a double hexameric (DH) helicase essential for replication initiation.

Purpose of the Study:

• To recapitulate the assembly process of the papillomavirus E1 initiator double hexameric (DH) helicase.
• To identify and characterize intermediates in the E1 helicase assembly pathway.
• To elucidate the mechanism by which the E1 initiator transitions from a dimer to a ring structure.

Main Methods:

• Recapitulation of papillomavirus E1 initiator DH helicase assembly in vitro.
• Identification and characterization of protein-DNA intermediates.
• Analysis of nucleotide binding and ATP hydrolysis requirements for complex formation.

Main Results:

• The study identified a novel intermediate: a double trimer (DT) in E1 helicase assembly.
• DT formation is dependent on nucleotide binding and facilitates DNA melting.
• DH helicase formation requires hydrolysable ATP and involves a transition from the DT intermediate.
• The DNA binding properties of the DT explain the transition from E1 dimers to ring structures.

Conclusions:

• The findings provide the first description of papillomavirus E1 initiator DH helicase assembly.
• A DT intermediate plays a key role in DNA melting and serves as a substrate for DH helicase formation.
• This work offers new insights into the molecular machinery governing DNA replication initiation by viral helicases.