diff --git a/content/3.defense-systems/nhi.md b/content/3.defense-systems/nhi.md index a3d556b07d3e8b3f646e87f3cb605fc3fc30b24d..685b244930892f01c866f7870eb57a02e440e3a0 100644 --- a/content/3.defense-systems/nhi.md +++ b/content/3.defense-systems/nhi.md @@ -6,13 +6,27 @@ tableColumns: doi: 10.1016/j.chom.2022.03.001 abstract: | The perpetual arms race between bacteria and their viruses (phages) has given rise to diverse immune systems, including restriction-modification and CRISPR-Cas, which sense and degrade phage-derived nucleic acids. These complex systems rely upon production and maintenance of multiple components to achieve antiphage defense. However, the prevalence and effectiveness of minimal, single-component systems that cleave DNA remain unknown. Here, we describe a unique mode of nucleic acid immunity mediated by a single enzyme with nuclease and helicase activities, herein referred to as Nhi (nuclease-helicase immunity). This enzyme provides robust protection against diverse staphylococcal phages and prevents phage DNA accumulation in cells stripped of all other known defenses. Our observations support a model in which Nhi targets and degrades phage-specific replication intermediates. Importantly, Nhi homologs are distributed in diverse bacteria and exhibit functional conservation, highlighting the versatility of such compact weapons as major players in antiphage defense. - Sensor: Unknown - Activator: Unknown - Effector: Nucleic acid degrading (?) + Sensor: Phage protein sensing + Activator: Direct binding + Effector: Nucleic acid degrading PFAM: PF01443, PF09848, PF13604 +contributors: + - Alba Herrero del Valle +relevantAbstracts: + - doi: 10.1016/j.chom.2022.03.001 + - doi: 10.1016/j.chom.2022.09.017 --- # Nhi + +## Description + +The Nhi (nuclease-helicase immunity) system targets and degrades specific phage DNA replication intermediates :ref{doi=10.1016/j.chom.2022.03.001}. Nayeemul Bari et al. showed that Nhi from *Staphylococcus epidermidis* protects against a diverse panel of staphylococcal phages and Millman et al. showed that a protein Nhi-like (that shares the domain organization with Nhi but not the sequence) from *Bacillus cereus* protects against some Bacillus phages :ref{doi=10.1016/j.chom.2022.03.001,10.1016/j.chom.2022.09.017}. + +## Molecular mechanisms + +Nhi contains two domains, a nuclease and a helicase domain that are both needed for the anti-phage activity. The nuclease domain has 3′–5′ exonuclease and plasmid nicking activities while the helicase unwinds dsDNA biderctionally. Nhi specifically recognizes phage single-stranded DNA binding proteins (SSB) that cover the phage genome to target this DNA for degradation thanks to its helicase and nuclease domains :ref{doi=10.1016/j.chom.2022.03.001}. + ## Example of genomic structure The Nhi system is composed of one protein: Nhi. @@ -108,13 +122,3 @@ end style Title3 fill:none,stroke:none,stroke-width:none style Title4 fill:none,stroke:none,stroke-width:none </mermaid> -## Relevant abstracts - -::relevant-abstracts ---- -items: - - doi: 10.1016/j.chom.2022.03.001 - ---- -:: -