Pycsar

Contributors: Lucas Paoli, Florian Tesson

Description

The pyrimidine cyclase system for antiphage resistance (Pycsar) () is composed of at least two proteins: a cyclase and diverse effectors. The Pycsar defense system is related to the CBASS but differs in the signaling molecule produced by the cyclase.

In turn, phages encode anti-Pycsar (Apyc) proteins encoded that counteract Pycsar defenses () .

Molecular mechanisms

Pycsar uses cyclic nucleotide (pyrimidine cyclase, cCMP and cUMP) signals to induce cell death via diverse effectors activation and prevent viral propagation.

While Apyc degrades cyclic nucleotide signals to prevent host immune responses (, ) .

Example of genomic structure

The Pycsar is composed of at least 2 proteins: a Cyclase and an Effector.

Like the CBASS system, it can encode for a variety of different effectors.

Here is an example found in the RefSeq database:

The Pycsar system in Nocardioides sambongensis (GCF_006494815.1, NZ_CP041091) is composed of 2 proteins 2TM_5 (WP_141014207.1) AG_cyclase (WP_141014208.1)

Distribution of the system among prokaryotes

Among the 22,803 complete genomes of RefSeq, the Pycsar is detected in 552 genomes (2.42 %).

The system was detected in 295 different species.

Proportion of genome encoding the Pycsar system for the 14 phyla with more than 50 genomes in the RefSeq database.

Structure

Experimentaly determined structure

From () in Burkholderia cepacia LK29:

Pycsar

Example 1
Example 2

Experimental validation

      
graph LR;
    Tal_2021[Tal et al., 2021] --> Origin_0
    Origin_0[Escherichia coli 
2684943848, 2742823945] --> Expressed_0[Escherichia coli]
    Expressed_0[Escherichia coli] ----> T5 & P1 & LambdaVir & SECphi27
    Tal_2021[Tal et al., 2021] --> Origin_1
    Origin_1[Xanthomonas perforans 
2637229924, 2628816548] --> Expressed_1[Escherichia coli]
    Expressed_1[Escherichia coli] ----> T7
    subgraph Title1[Reference]
        Tal_2021
end
    subgraph Title2[System origin]
        Origin_0
        Origin_1
end
    subgraph Title3[Expression species]
        Expressed_0
        Expressed_1
end
    subgraph Title4[Protects against]
        T5
        P1
        LambdaVir
        SECphi27
        T7
end
    style Title1 fill:none,stroke:none,stroke-width:none
    style Title2 fill:none,stroke:none,stroke-width:none
    style Title3 fill:none,stroke:none,stroke-width:none
    style Title4 fill:none,stroke:none,stroke-width:none

    

References

10.1016/j.cell.2021.09.031
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10.1038/s41586-022-04716-y
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