Huge thanks to my co-authors for such productive collaboration!

I am pretty sure more stories about (short) pAgos will certainly come from future studies...😊

In cells, this organization enables highly efficient elimination of cellular DNA, conferring bacterial immunity against plasmids and phages via abortive infection

Unlike SPARDA, we predict that SPARHA forms a chain of HNH domains with double active sites

Similar rearrangements leading to filament formation have been demonstrated for our first characterized system, SPARDA. doi.org/10.1038/s415... ; doi.org/10.1038/s414... ; doi.org/10.1038/s414...
Moreover, such rearrangements are also observed in other pAgos!

RNA-guide dependent target recognition induces conformational rearrangements in pAgo, causing significant shifts in the sensor loops SL1 and SL2, which in turn drive the connector loop (CL) forward and enable interactions with neighboring monomers

Congratulations!!! Fantastic news!

Exciting work!

I'm using clariostar plus - it works perfectly

Thank you so much, Daan!

congrats!

Thank you so much for sharing, François! I posted a thread with more details on my page — very glad to share this work and would be happy to discuss it!

We describe this beautiful mechanism in our preprint:
www.biorxiv.org/content/10.1...
Huge thanks to all co-authors — and especially to my advisor, Andrey Kulbachinskiy — for invaluable support and collaboration!!!

SPARHA represents a two-component defense system based on a suicidal cellular response, in which activation of the HNH effector by the pAgo sensor leads to filament formation, promoting efficient degradation of invading nucleic acids.

We further show that activation of SPARHA by the interfering plasmid depends on the binding of guide RNAs derived from the plasmid origin of replication.

In cells, SPARHA is activated in the presence of invaders, cleaving cellular DNA and conferring protection to the bacterial population via an abortive infection mechanism.

Target DNA recognition induces conformational changes of SPARHA, freeing the HNH domains and promoting their dimerization. Subsequent association of HNH dimers leads to formation of right-handed HNH-pAgo filaments containing dimeric active sites capable of double-stranded DNA cleavage.

Unlike the DREN domain of SPARDA systems, the HNH nuclease of SPARDA is highly active in the absence of short pAgo but is kept in a silent state by pAgo until target recognition. Using SEC, TEM, AF3 modeling, and site-directed mutagenesis, we were able to reveal the activation mechanism of SPARHA.

Now, we present SPARHA, a new defense system from a distinct clade of short pAgos associated with predicted HNH nuclease effectors. SPARHA is activated after guide RNAs binding and target DNA recognition, leading to cleavage of dsDNA substrates.

Previously, we characterized the SPARDA system: a complex of short pAgo and DREN nuclease, which cleaves DNA and RNA substrates upon target DNA recognition and is activated in the presence of plasmids or phages, inducing cell death or dormancy. www.nature.com/articles/s41...