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Running in reverse: the structural basis for translocation polarity in hexameric helicases
Nathan D Thomsen1, James M Berger
1Department of Molecular and Cell Biology, Quantitative Biosciences Institute, University of California, Berkeley, CA 94720, USA.
Cell
|November 3, 2009
Summary
This study reveals how RecA-like helicases bind RNA, showing structural similarities to AAA+ helicases. These enzymes use distinct ATP states and reversed ATPase site order for translocation.
Area of Science:
- Molecular Biology
- Biochemistry
- Structural Biology
Background:
- Hexameric helicases are crucial for DNA replication, repair, and gene expression.
- They exist in two families with opposite translocation polarities: AAA+ (3' to 5') and RecA-like (5' to 3').
Purpose of the Study:
- To elucidate the mechanism of RecA-like helicase engagement and translocation on RNA.
- To understand the structural basis of Rho transcription termination factor function.
Main Methods:
- X-ray crystallography was used to determine the structure of E. coli Rho bound to RNA and nucleotide.
- Comparative structural analysis with AAA+ helicase E1 was performed.
Main Results:
- The structure revealed interior nucleic acid-binding elements spiraling around RNA, resembling AAA+ helicases.
- Four distinct ATP-binding states, indicative of catalytic intermediates, were identified and linked to RNA positioning via an allosteric network.
- RecA-like and AAA+ helicases exhibit differences in their chemomechanical cycles and ATPase site firing order for translocation.
Conclusions:
- RecA-like helicases share unexpected structural features with AAA+ helicases.
- ATP hydrolysis states and allosteric networks are critical for RNA translocation.
- Opposing translocation polarities arise from distinct mechanisms within the hexameric ring.
