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Very cool work @rafomics.bsky.social @arturocdr.bsky.social and @guillermo-montoya.bsky.social!!

Congratulations @audeber.bsky.social ! Very well deserved!

Congratulations Friedrich!

Congratulations Ilya!

Another study on Druantia by the He laboratory: www.biorxiv.org/content/10.6...

Thank you Amar! Hope all is well!

Thank you Owen!

Thank you Melanie! Indeed very reminiscent of the DdmDE mechanism🤩. Had to keep the color scheme consistent 🙂.

Thank you Theo!! 🙂

Also check out the three(!!!) other complementary studies by the labs of: @fnobrega.bsky.social: www.biorxiv.org/content/10.6... Chase Beisel: www.biorxiv.org/content/10.6... Nicholas Taylor: www.biorxiv.org/content/10.6...

Finally, a huge thank you to Christelle Chanez and @martinjinek.bsky.social. This story would not have been possible without their support, insights and contributions along the way.

Together, our data support a model in which DruH processes replication-associated forked DNA structures to generate 5′ overhangs that trigger activation of the autoinhibited helicase–nuclease DruE, enabling selective DNA degradation during phage defense.

DruE loads onto the 3′ strand, raising the question of how DruH exonuclease activity promotes DruE activation. Unwinding assays show that DruE initiates on substrates with 5′ overhangs, while blocking the 3′ strand with streptavidin prevents helicase loading and strongly inhibits activity.

The structure of the holo-complex reveals that the C-terminal domain of DruH directly engages DruE and promotes loading of monomeric DruE onto the 3′ overhang.

Next, we used pulldown assays to identify the preferred DNA substrate of Druantia and determined the structure of the DruE–DruH holo-complex. We find that forked DNA substrates promote assembly of a DNA-bound complex between DruH and monomeric DruE, forming a 1:1 complex.

Next, we determined the structure of DruE, a large dimeric helicase–nuclease. The structure reveals an autoinhibited assembly, while biochemical reconstitution and phage assays show that DruE couples ATP-dependent DNA unwinding to nuclease-mediated DNA degradation both essential for immunity.

Given the predicted helicase activity of druE, we hypothesized that Type III Druantia directly targets phage-derived nucleic acids. Guided by AF3 predictions and biochemical assays, we find that DruH functions as a 3′-5′ exonuclease that processes DNA substrates containing exposed 3′ termini.

To understand the function of DruH, we solved its structure using cryo-EM. DruH is a multidomain protein containing α-helical N- and C-terminal domains connected by six central Ig-like domains.

We find that Druantia both DruE and DruH are essential for immunity. Interestingly, infected cells continue to grow during phage challenge, indicating that Type III Druantia does not function through an abortive infection mechanism.

Type III Druantia is a two-component defense system consisting of the signature gene druE, a predicted helicase, and druH a large accessory protein of unknown function. To understand the mechanism underlying Druantia immunity, we focused on the Type III system from Pseudomonas aeruginosa.