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Elife. 2018 Dec 24;7. pii: e41140. doi: 10.7554/eLife.41140.

Mechanisms of opening and closing of the bacterial replicative helicase.

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Department of Chemistry and Biochemistry, City College of New York, New York, United States.
PhD Program in Biochemistry, The Graduate Center of the City University of New York, New York, United States.
Simons Electron Microscopy Center, The New York Structural Biology Center, New York, United States.
Laboratory for Mass Spectrometry and Gaseous Ion Chemistry, The Rockefeller University, New York, United States.
Department of Biochemistry, Center for Excellence in Protein and Enzyme Technology, Faculty of Science, Mahidol University, Bangkok, Thailand.
Department of Molecular and Cellular Biology, Harvard University, Cambridge, United States.
Structural Biology Initiative, CUNY Advanced Science Research Center, New York, United States.
PhD Program in Chemistry, The Graduate Center of the City University of New York, New York, United States.
PhD Program in Biology, The Graduate Center of the City University of New York, New York, United States.


Assembly of bacterial ring-shaped hexameric replicative helicases on single-stranded (ss) DNA requires specialized loading factors. However, mechanisms implemented by these factors during opening and closing of the helicase, which enable and restrict access to an internal chamber, are not known. Here, we investigate these mechanisms in the Escherichia coli DnaB helicase•bacteriophage λ helicase loader (λP) complex. We show that five copies of λP bind at DnaB subunit interfaces and reconfigure the helicase into an open spiral conformation that is intermediate to previously observed closed ring and closed spiral forms; reconfiguration also produces openings large enough to admit ssDNA into the inner chamber. The helicase is also observed in a restrained inactive configuration that poises it to close on activating signal, and transition to the translocation state. Our findings provide insights into helicase opening, delivery to the origin and ssDNA entry, and closing in preparation for translocation.


DNA replication; DnaB replicative helicase; E. coli; biochemistry; chemical biology; cryogenic electron microscopy; helicase loader; molecular biophysics; replication initiation; structural biology

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