SNIPE: Membrane-Bound Nuclease Anti-Phage Defence

Overview

SNIPE (Surface-associated Nuclease Inhibiting Phage Entry) is a bacterial anti-phage defence system that cleaves phage DNA during genome injection. It represents a novel self/non-self discrimination strategy in prokaryotic immunity, distinct from CRISPR-Cas (sequence recognition) and restriction-modification (DNA modification recognition). SNIPE exploits the spatial organization of phage genome injection — the fact that phage DNA must pass through the cell membrane — to specifically target foreign DNA.

Key paper: Saxton DS, DeWeirdt PC, Doering CR, Roney IJ & Laub MT (2026). A membrane-bound nuclease directly cleaves phage DNA during genome injection. Nature. https://doi.org/10.1038/s41586-026-10207-1

Previous identification: Vassallo CN, Doering CR, Littlehale ML, Teodoro GIC & Laub MT (2022). A functional selection reveals previously undetected anti-phage defence systems in the E. coli pangenome. Nat. Microbiol. 7:1568-1579. (Originally named PD-lambda-1.)

Mechanism

1. SNIPE is a ~500 aa inner membrane protein with three domains:
2. N-terminal transmembrane domain (aa 5-24): anchors to inner membrane
3. DUF4041 domain (aa ~144-262): binds DNA; interacts with phage tape measure proteins (TMPs)
4. GIY-YIG nuclease domain (aa ~357-450): cleaves phage DNA (catalytic residue E414)
5. SNIPE pre-associates with ManYZ (mannose permease) in the inner membrane before infection
6. During phage genome injection, DUF4041 binds the phage tape measure protein, positioning the nuclease to cleave incoming DNA
7. This provides direct defence — the infected cell survives (unlike abortive infection systems)
8. SNIPE also provides ManYZ-independent defence against siphoviruses via weak TMP interactions

InterPro / Pfam

• IPR025280 — "SNIPE associated domain" (recently renamed from DUF4041 to reflect this paper)
• PF13250 — Pfam entry for DUF4041
• 1,612 protein matches across 1,044 proteomes and 2,466 taxa
• ~500 curated SNIPE homologues across many bacterial phyla
• 33% of well-sequenced bacterial clades harbour at least one SNIPE homologue

Key Proteins

SNIPE (PD-lambda-1)

• UniProt TrEMBL: A0A8T9CRB7 (best match; no Swiss-Prot entry)
• GenBank: RCP76574.1 (from E. coli MOD1-ECOR26, locus APT27_20780)
• RefSeq: WP_001606968.1
• Not present in E. coli K-12 MG1655 — encoded in prophage elements of wild E. coli strains

E. coli host proteins involved

Phage lambda proteins

Evolutionary Diversity of SNIPE Homologues

SNIPE homologues show a modular architecture with highly diversified N-terminal regions:
- 59% harbour one transmembrane domain
- 7% harbour two transmembrane domains
- 34% lack predicted TM domains — these use alternative membrane-targeting strategies:
- DivIVA domains (negative membrane curvature binding)
- Type III secretion system domains
- Pleckstrin homology domains (phospholipid binding)
- Phage tail protein fusions

The GIY-YIG nuclease domain is the most conserved region. The DUF4041 domain shows moderate conservation with a positively charged DNA-binding interface. The N-terminal region has the highest variability, suggesting it functions as an adapter for phage specificity.

GO Annotation Considerations

Potential GO terms for SNIPE

• Molecular Function: endonuclease activity (GIY-YIG family); DNA binding; protein binding (tape measure protein)
• Biological Process: defence response to bacteriophage; DNA catabolic process; negative regulation of viral genome replication
• Cellular Component: integral component of plasma membrane

Annotation challenges

1. No existing GO term captures "cleavage of foreign DNA during membrane injection"
2. The DUF4041 domain has dual function (DNA binding + TMP binding) — needs careful annotation
3. Direct defence vs. abortive infection distinction matters for BP annotation
4. The ManYZ interaction is pre-infection positioning, not a canonical "protein complex"

Potential new GO terms

• "phage genome injection site" (CC) — for membrane complexes at injection points
• "defence response to bacteriophage via direct DNA cleavage" (BP) — to distinguish from abortive infection
• "tape measure protein binding" (MF) — specific interaction that enables SNIPE targeting

GIY-YIG InterPro-to-GO Misannotation Risk

The InterPro-to-GO mapping (rules/arba/_interpro2go.txt) contains:

InterPro:IPR047296 UvrC/Cho-like, GIY-YIG domain → GO:0006289 (nucleotide-excision repair)

This mapping assumes GIY-YIG = DNA repair (as in UvrC), but SNIPE demonstrates this domain has been repurposed for antiphage defence. Automated annotation of SNIPE homologues through this InterPro entry would produce incorrect GO annotations for 500+ proteins. This should be flagged when proposing InterPro2GO mappings for PF13250/IPR025280.

Cross-References to Related Genes in Repo

DivIVA membrane anchoring (BACSU)

genes/BACSU/divIVA/divIVA-ai-review.yaml (P71021) — ~34% of SNIPE homologues lacking transmembrane domains use DivIVA-like domains for membrane anchoring. The DivIVA review covers the same membrane curvature-sensing mechanism these SNIPE variants use.

Phage-bacteria arms race genes

Related projects

Genes for Review

Key References

• Saxton et al. (2026) Nature — SNIPE characterization (PMID:41741653)
• Vassallo et al. (2022) Nat Microbiol 7:1568-1579 — Original identification as PD-lambda-1
• Maffei et al. (2021) PLoS Biol 19:e3001424 — BASEL phage collection
• Branon et al. (2018) Nat Biotechnol 36:880-887 — TurboID proximity labelling
• Hallgren et al. (2022) bioRxiv — DeepTMHMM transmembrane prediction

STATUS

Completed

• [x] Read and summarize Saxton et al. 2026
• [x] Full gene review of SNIPE (A0A8T9CRB7) — genes/ECOLX/SNIPE/SNIPE-ai-review.yaml
• [x] Assess whether new GO terms are needed — proposed 2 new terms in review
• [x] Draft GO issue for antiviral nucleic acid defence hierarchy — projects/SNIPE/go-issue-antiviral-nucleic-acid-defense.md

Pending

• [ ] Check current GO annotations for SNIPE homologues
• [ ] Review SNIPE homologue diversity and domain architecture annotations in InterPro
• [ ] Cross-reference with DefenseFinder database entries
• [ ] Propose InterPro2GO mappings for PF13250/IPR025280 (currently none exist)
• [ ] Add literature references to IPR025280 (currently none linked)
• [ ] Flag GIY-YIG InterPro-to-GO misannotation concern (IPR047296 → GO:0006289)

Last updated: 2026-03-01

NOTES

2026-03-01

Project Creation

Created from reading Saxton et al. (2026) Nature paper on SNIPE.

Key observations:
- IPR025280 (formerly DUF4041) has already been renamed to "SNIPE associated domain" in InterPro, with description updated to reference the cleavage mechanism. This suggests InterPro curators updated the entry around publication.
- SNIPE represents a genuinely novel immune mechanism — not sequence-based (like CRISPR) or modification-based (like R-M), but localization-based.
- Conceptual parallel to eukaryotic IFITM proteins that block viral entry at membranes.
- The modular N-terminal diversity across ~500 homologues is an interesting case for studying domain shuffling and functional diversification.