Cryo-EM Structure of a Relaxase Reveals the Molecular Basis of DNA Unwinding during Bacterial Conjugation

Relaxases play essential roles in conjugation, the main process by which bacteria exchange genetic material, notably antibiotic resistance genes. They are bifunctional enzymes containing a trans-esterase activity, which is responsible for nicking the DNA strand to be transferred and for covalent att...

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Bibliographic Details
Published in:Cell 2017-05, Vol.169 (4), p.708-721.e12
Main Authors: Ilangovan, Aravindan, Kay, Christopher W.M., Roier, Sandro, El Mkami, Hassane, Salvadori, Enrico, Zechner, Ellen L., Zanetti, Giulia, Waksman, Gabriel
Format: Article
Language:English
Subjects:
bacterial conjugation
Conjugation, Genetic
cryo-electron microscopy
Cryoelectron Microscopy
DNA Helicases - chemistry
DNA Helicases - metabolism
DNA Helicases - ultrastructure
DNA, Bacterial - chemistry
DNA, Bacterial - ultrastructure
DNA, Single-Stranded - chemistry
DNA, Single-Stranded - metabolism
Escherichia coli - enzymology
Escherichia coli - genetics
Escherichia coli - metabolism
Escherichia coli Proteins - chemistry
Escherichia coli Proteins - metabolism
Escherichia coli Proteins - ultrastructure
Models, Molecular
relaxase
structural biology
TraI
type IV secretion system
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Summary:Relaxases play essential roles in conjugation, the main process by which bacteria exchange genetic material, notably antibiotic resistance genes. They are bifunctional enzymes containing a trans-esterase activity, which is responsible for nicking the DNA strand to be transferred and for covalent attachment to the resulting 5′-phosphate end, and a helicase activity, which is responsible for unwinding the DNA while it is being transported to a recipient cell. Here we show that these two activities are carried out by two conformers that can both load simultaneously on the origin of transfer DNA. We solve the structure of one of these conformers by cryo electron microscopy to near-atomic resolution, elucidating the molecular basis of helicase function by relaxases and revealing insights into the mechanistic events taking place in the cell prior to substrate transport during conjugation. [Display omitted] •Relaxases process and transfer plasmid DNAs during conjugation•The TraI relaxase binds the origin of transfer DNA as a dimer•TraI can adopt a closed and open conformation, and both co-exist in the dimer•The presented ssDNA-bound TraI structure reveals the closed “helicase” conformation To achieve genetic exchange during bacterial conjugation, two relaxase monomers collaborate, adopting distinct structural conformations to provide the two necessary enzymatic activities for processing the DNA.
ISSN:0092-8674
1097-4172
DOI:10.1016/j.cell.2017.04.010