SNIPE (Surface-associated Nuclease Inhibiting Phage Entry) is a 500 amino acid inner membrane-bound GIY-YIG family DNA endonuclease that provides direct anti-bacteriophage defence in Escherichia coli. SNIPE constitutively localizes to the inner membrane via an N-terminal single-pass transmembrane helix (aa 5-24) and pre-associates with the ManYZ mannose permease complex before phage infection. During phage genome injection, the central DUF4041 domain (aa 144-262, now designated the SNIPE-associated domain, IPR025280) binds both incoming phage DNA and the phage tape measure protein (TMP), positioning the C-terminal GIY-YIG nuclease domain (aa 357-450, catalytic residue E414) to cleave phage DNA as it crosses the inner membrane. This provides direct defence β the infected cell survives β in contrast to abortive infection systems. SNIPE does not affect phage adsorption, does not target pre-existing intracellular phage genomes (lysogens), and does not block plasmid transformation, indicating its activity is specific to the phage genome injection process. Originally identified as PD-lambda-1 in a functional screen of 71 diverse E. coli pangenomes (PMID:36123438), SNIPE homologues (~500 curated) are found across many bacterial phyla, with 33% of well-sequenced clades harbouring at least one homologue. The N-terminal region is highly variable and functions as a phage-specificity adapter, with 59% of homologues having one TM domain, 7% having two, and 34% using alternative membrane-targeting strategies (DivIVA domains, type III secretion domains, PH domains). SNIPE represents a previously unknown self/non-self discrimination strategy based on subcellular localization rather than sequence recognition (CRISPR-Cas) or modification detection (restriction-modification). Note: UniProt entry A0A8T9CRB7 is from E. coli strain T0181B.E-10. The experimentally characterized SNIPE was from strain MOD1-ECOR26 (GenBank RCP76574.1, locus APT27_20780). Both share RefSeq WP_001606968.1. SNIPE is not present in E. coli K-12 MG1655.
Definition: A defense response to a virus in which a membrane-anchored nuclease of the SNIPE family cleaves viral DNA during genome injection across the cell membrane. SNIPE proteins associate with inner membrane components at phage genome injection sites, bind phage tape measure proteins via their DUF4041 domain, and use a GIY-YIG nuclease domain to degrade incoming phage DNA before it enters the cytoplasm. Unlike restriction-modification or CRISPR-Cas systems, self/non-self discrimination is achieved through subcellular localization at the membrane rather than recognition of specific DNA sequences or modifications.
Justification: The current anti-foreign nucleic acid branch (GO:0099046 clearance of foreign intracellular nucleic acids) does not capture SNIPE mechanism, because SNIPE cleaves phage DNA during translocation at the membrane before the DNA becomes intracellular. A dedicated term under GO:0051607 (defense response to virus) is needed to represent this direct anti-phage mechanism.
Parent term: defense response to virus
Supporting Evidence:
Definition: A defense response to a virus in which the host targets viral nucleic acid for degradation or modification, preventing viral replication. Includes systems that act on nucleic acid after cell entry (e.g. CRISPR-Cas, restriction-modification) and systems that act during genome injection (e.g. SNIPE).
Justification: Optional intermediate grouping term matching the GO issue proposal. This would provide a clean parent for nucleic acid-targeting anti-viral systems such as CRISPR-Cas, restriction-modification, and SNIPE while preserving mechanistic distinctions in child terms.
Parent term: defense response to virus
Supporting Evidence:
| GO Term | Evidence | Action | Reason |
|---|---|---|---|
| GO:0004520 DNA endonuclease activity | IDA PMID:41741653 A membrane-bound nuclease directly cleaves phage DNA during ... | NEW | Summary: SNIPE contains a C-terminal GIY-YIG nuclease domain (aa 357-450) that endonucleolytically cleaves phage DNA during genome injection. Substitution of the predicted catalytic residue E414 to alanine abolishes both nuclease activity and phage defence (PMID:41741653). Radiolabelled 32P phage DNA is degraded from ~42 kb to fragments <100 bp and mononucleotides in SNIPE-expressing cells, dependent on E414 (PMID:41741653). The pattern of degradation (smear of fragments rather than defined products) is consistent with endonucleolytic cleavage, though in vitro reconstitution has not yet been performed. The GIY-YIG nuclease domain is the most conserved region across ~500 SNIPE homologues (PMID:41741653), and domain-level homology to the T5orf172/MUG113 family of GIY-YIG endonucleases is confirmed by InterPro/Pfam assignments (IPR018306, PF13455). GO:0004520 is the appropriate level of specificity; there is no GIY-YIG-specific child term in GO, and the data do not support a more specific term like GO:0015666 (restriction endodeoxyribonuclease activity) since SNIPE does not recognize specific DNA sequences or modification states. Reason: Core molecular function of SNIPE, directly demonstrated by multiple experimental approaches in PMID:41741653: (1) 32P-labelled phage DNA cleavage assay showing degradation during injection, (2) E414A catalytic dead mutant abolishing cleavage and defence, (3) Gam-GFP double-strand break reporter showing SNIPE-dependent foci, (4) CFP-ParB foci reduced ~30-fold indicating DNA degradation during injection. The domain architecture (GIY-YIG nuclease, IPR018306/PF13455) independently supports endonuclease activity via homology to biochemically characterized family members. IDA evidence code is appropriate because the nuclease activity was directly assayed in vivo using radiolabelled substrate and catalytic mutant controls. Supporting Evidence: PMID:41741653 we demonstrate that SNIPE directly cleaves phage DNA during genome injection PMID:41741653 Using radiolabelled phage DNA and time-lapse microscopy to track phage genomes, we demonstrate that SNIPE directly cleaves phage DNA during genome injection PMID:36123438 a putative membrane-anchored protein with a central coiled-coil domain (DUF4041) and a C-terminal DNA binding/cleavage domain file:ECOLX/SNIPE/SNIPE-deep-research-falcon.md T5orf172 is a subfamily of GIY-YIG endonucleases ... the two profiles [T5orf172 and MUG113] are highly related |
| GO:0003690 double-stranded DNA binding | IDA PMID:41741653 A membrane-bound nuclease directly cleaves phage DNA during ... | NEW | Summary: The DUF4041/SNIPE-associated domain (aa 144-262) of SNIPE has a positively charged surface that facilitates DNA binding. When the TM domain is removed (SNIPE(deltaTM E414A)-GFP), the protein co-localizes with the DAPI-stained nucleoid (Pearson R=0.76), and this co-localization is abolished when DUF4041 is also deleted (deltaDUF4041 shows R=0.13) (PMID:41741653). A DUF4041-only fusion to GFP also localizes to the nucleoid. ConSurf analysis shows the positively charged DNA-binding interface is conserved across SNIPE homologues (PMID:41741653). Note that the evidence for DNA binding is based on fluorescence microscopy co-localization with the nucleoid rather than a direct biochemical binding assay (e.g. EMSA); however, the domain-dependent co-localization pattern and the conserved positively charged surface provide strong support for direct DNA binding. Phage lambda DNA is dsDNA, making GO:0003690 the appropriate specific term. The original identification also noted the C-terminal region as a "DNA binding/cleavage domain" (PMID:36123438). Reason: DNA binding by DUF4041 is demonstrated by microscopy showing domain-dependent nucleoid co-localization (PMID:41741653): removal of DUF4041 abolishes nucleoid association. This is further supported by the conserved positively charged surface identified by ConSurf analysis across ~500 homologues, and by domain annotation as a DNA-binding domain (IPR018306 Phage_T5_Orf172_DNA-bd). IDA evidence code is appropriate for microscopy-based localization experiments with domain deletion controls. The term GO:0003690 (double-stranded DNA binding) is preferred over GO:0003677 (DNA binding) because phage lambda DNA is dsDNA and the nucleoid is dsDNA. Supporting Evidence: PMID:36123438 a putative membrane-anchored protein with a central coiled-coil domain (DUF4041) and a C-terminal DNA binding/cleavage domain |
| GO:0051607 defense response to virus | IDA PMID:41741653 A membrane-bound nuclease directly cleaves phage DNA during ... | NEW | Summary: SNIPE provides direct defence against bacteriophage lambda and diverse siphoviruses. SNIPE-expressing cells survive phage lambda infection at high MOI where control cells lyse (PMID:41741653). Defence is demonstrated by: time-lapse microscopy showing cell survival, growth curves at MOI 0.1-10, plaque assays showing 6-7 log reduction in phage titre, and the BASEL collection screen showing protection against diverse siphoviruses (both ManYZ-dependent and ManYZ-independent) (PMID:41741653). SNIPE provides direct defence (cell survival) rather than abortive infection. It was originally identified as one of 21 novel defence systems in a functional metagenomic screen of the E. coli pangenome (PMID:36123438). Reason: Defence against bacteriophage is the primary evolved biological function of SNIPE, supported by multiple complementary experimental approaches (PMID:41741653) and by its original identification via a functional anti-phage defence screen (PMID:36123438). GO:0051607 (defense response to virus) is the most specific existing BP term. There is currently no GO term for "defense response to bacteriophage" specifically; a new term request has been drafted (see projects/SNIPE/go-issue-antiviral-nucleic-acid-defense.md). IDA evidence code is appropriate as defence was directly assayed by growth curves, plaque assays, and single-cell microscopy. Supporting Evidence: PMID:41741653 we characterize SNIPE, an anti-bacteriophage defence system that constitutively localizes to the bacterial cell membrane in Escherichia coli to block phage PMID:41741653 SNIPE as a widespread bacterial defence system that exploits the spatial organization of phage genome injection to specifically target viral DNA, representing a previously unknown strategy for distinguishing self from non-self in prokaryotic immune systems PMID:36123438 Our results unveil 21 conserved defence systems, none of which were previously detected as enriched in defence islands |
| GO:0045071 negative regulation of viral genome replication | IDA PMID:41741653 A membrane-bound nuclease directly cleaves phage DNA during ... | NEW | Summary: SNIPE prevents phage genome replication by destroying the phage DNA during the injection process, before the genome enters the cytoplasm intact. CFP-ParB foci (a proxy for phage genome establishment) are reduced ~30-fold in SNIPE-expressing cells (PMID:41741653). Phage produced per cell is not significantly different between SNIPE and empty vector when inducing lysogens, confirming that SNIPE targets the injection step specifically and does not affect pre-existing intracellular phage genomes (PMID:41741653). While the net effect is prevention of viral genome replication, the mechanism is more precisely described as destruction of the phage genome during membrane translocation rather than regulation of replication per se. GO:0046597 (host-mediated suppression of symbiont invasion) may be a more mechanistically precise BP term since SNIPE blocks the entry/establishment of the phage genome rather than regulating its replication after entry. Reason: The outcome of SNIPE activity is that viral genome replication is completely prevented, making GO:0045071 a defensible annotation. The evidence is strong: CFP-ParB foci reduction demonstrates that phage genomes do not establish in SNIPE-expressing cells (PMID:41741653). However, SNIPE acts upstream of replication -- it destroys the DNA during injection, not by regulating the replication machinery. This distinction may matter for precision. The annotation is retained because the net biological outcome (no viral genome replication) is accurately captured. See also the additional GO:0046597 annotation below for a more mechanistically precise complementary term. IDA evidence code is appropriate. Supporting Evidence: PMID:41741653 we demonstrate that SNIPE directly cleaves phage DNA during genome injection PMID:41741653 SNIPE associates with host proteins essential for lambda genome entry and with the lambda tape measure protein, which facilitates lambda genome injection across the inner membrane |
| GO:0046597 host-mediated suppression of symbiont invasion | IDA PMID:41741653 A membrane-bound nuclease directly cleaves phage DNA during ... | NEW | Summary: SNIPE inhibits phage genome entry into the bacterial cell by cleaving phage DNA during the injection process at the inner membrane. This directly suppresses the phage's invasion of the host cell. GO:0046597 is defined as "a process in which a host inhibits or disrupts the entry of a symbiont into a host cell." While bacteriophages inject their genome rather than entering bodily, the phage genome translocation across the inner membrane constitutes the functional "entry" event that SNIPE suppresses. SNIPE does not block phage adsorption to the cell surface -- phage adsorption is unaffected (PMID:41741653) -- but it destroys the phage DNA during membrane translocation, preventing genome establishment. This term complements GO:0045071 by providing a more mechanistically precise description of SNIPE's biological role. Reason: SNIPE acts specifically at the step of phage genome injection across the inner membrane (PMID:41741653). It does not affect phage adsorption, does not target pre-existing lysogens, and does not block plasmid transformation -- it is specific to the injection process. GO:0046597 (host-mediated suppression of symbiont invasion) captures this specificity better than GO:0045071 (negative regulation of viral genome replication), which implies action on the replication process itself. GO:0046597 is the parent of several relevant child terms in GO and is compatible with bacterial hosts defending against phage. IDA evidence code is appropriate. Supporting Evidence: PMID:41741653 we characterize SNIPE, an anti-bacteriophage defence system that constitutively localizes to the bacterial cell membrane in Escherichia coli to block phage PMID:36123438 We confirmed that each system did not affect phage adsorption (Extended Data Fig |
| GO:0006308 DNA catabolic process | IDA PMID:41741653 A membrane-bound nuclease directly cleaves phage DNA during ... | NEW | Summary: SNIPE degrades phage DNA from ~42 kb to fragments less than 100 bp and mononucleotides during genome injection (PMID:41741653). This is a DNA catabolic process -- the breakdown of DNA. The 32P-labelled DNA tracking experiment directly demonstrates catabolism of the phage DNA substrate. While the MF annotation (GO:0004520 DNA endonuclease activity) captures the catalytic mechanism, GO:0006308 captures the biological process of DNA degradation that results from this activity. Reason: The degradation of phage DNA from intact genomic molecules (~42 kb) to small fragments (<100 bp) and mononucleotides is directly demonstrated by the 32P-labelled DNA cleavage assay (PMID:41741653). This constitutes DNA catabolism. GO:0006308 provides a process-level annotation that complements the molecular function (GO:0004520) and the higher-level biological context (GO:0051607 defense response to virus). IDA evidence code is appropriate as the catabolic activity was directly measured using radiolabelled substrate. Supporting Evidence: PMID:41741653 we demonstrate that SNIPE directly cleaves phage DNA during genome injection |
| GO:0005886 plasma membrane | IDA PMID:41741653 A membrane-bound nuclease directly cleaves phage DNA during ... | NEW | Summary: SNIPE is an integral inner membrane protein with a single-pass TM helix (aa 5-24). Topology was confirmed by PhoA-LacZalpha fusion analysis: PhoA was active only when inserted at the N-terminus (periplasmic side), and LacZalpha was active only when inserted downstream of the TM domain (cytoplasmic side) (PMID:41741653). SNIPE-GFP localizes uniformly to the cell membrane by fluorescence microscopy (PMID:41741653). Immunoblotting of fractionated cell lysates shows SNIPE is strongly enriched in the membrane fraction (PMID:41741653). DeepTMHMM and Phobius both predict a transmembrane helix at residues 6-24, consistent with the UniProt annotation (ECO:0000256|SAM:Phobius). In bacteria, GO:0005886 (plasma membrane) corresponds to the inner/cytoplasmic membrane. The single-pass TM helix makes SNIPE an integral (not peripheral) component of the plasma membrane. GO has merged GO:0005887 (integral component of plasma membrane) into GO:0005886, so plasma membrane is the term to use. Reason: Integral membrane localization is directly demonstrated by three independent experimental approaches in PMID:41741653: (1) PhoA/LacZalpha topology mapping confirming transmembrane orientation, (2) fluorescence microscopy of SNIPE-GFP showing uniform membrane localization, (3) membrane fractionation/immunoblotting showing enrichment in membrane fraction. This is further supported by the predicted TM helix (Phobius, DeepTMHMM) in the UniProt record. GO:0005886 (plasma membrane) is used because GO has merged GO:0005887 (integral component of plasma membrane) into it. IDA evidence code is appropriate for the topology mapping and fractionation experiments. Supporting Evidence: PMID:41741653 an anti-bacteriophage defence system that constitutively localizes to the bacterial cell membrane in Escherichia coli PMID:41741653 Here, we characterize SNIPE, an anti-bacteriophage defence system that constitutively localizes to the bacterial cell membrane in Escherichia coli to block phage Ξ» infection |
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Download this section (compressed HTML)Q: Is GO:0004520 (DNA endonuclease activity) the correct MF term for SNIPE, or should a more specific child term (e.g. reflecting GIY-YIG family membership or the membrane-localized context) be used?
Q: Should the ManYZ pre-association be annotated as a separate protein complex, or is it better modelled as a GO-CAM causal association (SNIPE located_in plasma membrane, colocalizes_with ManYZ complex)?
Q: Does the tape measure protein (TMP) binding by DUF4041 warrant a specific MF annotation (e.g. viral protein binding) or is this better captured only in the GO-CAM model?
Experiment: The 32P cleavage assay (Fig 2d) shows a smear of fragments consistent with endonucleolytic cleavage, but the exact cleavage mechanism and products have not been biochemically characterized with purified SNIPE. In vitro reconstitution of SNIPE nuclease activity with defined DNA substrates would confirm endonuclease vs exonuclease activity, determine sequence specificity (if any), and characterize cleavage products.
Hypothesis: SNIPE cleaves phage DNA endonucleolytically (producing internal cuts) rather than exonucleolytically
Type: Biochemical assay
Experiment: Test representative SNIPE homologues lacking TM domains for phage defence in their native hosts or heterologous expression. Determine whether these homologues also pre-associate with inner membrane proteins at genome injection sites, and whether their N-terminal domains dictate phage specificity.
Hypothesis: SNIPE homologues with non-TM N-terminal regions (DivIVA, T3SS, PH domain) use analogous mechanisms but target different phage entry pathways
Type: Genetics/Functional assay
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