Anti-DarT factor A (AdfA; gp61.2) is a 208-amino-acid counter-defense protein of bacteriophage T4 that antagonizes the bacterial DarTG toxin-antitoxin anti-phage defense system. Functioning as a non-enzymatic antitoxin mimic in the infected host cytoplasm, AdfA inhibits the host DarT DNA ADP-ribosyltransferase toxin, preventing ADP-ribosylation of viral DNA and allowing phage genome replication and productive infection to proceed.
| GO Term | Evidence | Action | Reason |
|---|---|---|---|
| GO:0052031 symbiont-mediated perturbation of host defense response | IEA GO_REF:0000043 | MODIFY | Summary: Broad parent process term that should be refined to the more specific descendant GO:0052170 (symbiont-mediated suppression of host innate immune response) already annotated to the gene. Reason: AdfA specifically suppresses the bacterial DarTG innate anti-phage defense system by inhibiting the DarT DNA ADP-ribosyltransferase toxin, which is more precisely captured by the descendant term GO:0052170 already present on this gene. Proposed replacements: symbiont-mediated suppression of host innate immune response Supporting Evidence: file:BPT4/adfA/adfA-deep-research-falcon.md **Primary functional role:** AdfA is a phage-encoded **anti-defense** factor that counteracts DarTG-mediated defense by **inhibiting DarT toxin activity**, preventing detectable ADP-ribosylation of phage DNA in the escape context, and thereby restoring productive infection. file:BPT4/adfA/adfA-uniprot.txt Plays a role in counteracting the host DarT defense system. {ECO:0000250|UniProtKB:Q7Y5A4}. |
| GO:0052170 symbiont-mediated suppression of host innate immune response | IEA GO_REF:0000043 | ACCEPT | Summary: Accurately captures AdfA's role in suppressing the host bacterial DarTG anti-phage defense system. Reason: AdfA directly counteracts the host DarTG innate anti-phage toxin-antitoxin system by inhibiting the DarT DNA ADP-ribosyltransferase toxin, and no more specific GO term for DarTG evasion currently exists. Supporting Evidence: file:BPT4/adfA/adfA-deep-research-falcon.md **Primary functional role:** AdfA is a phage-encoded **anti-defense** factor that counteracts DarTG-mediated defense by **inhibiting DarT toxin activity**, preventing detectable ADP-ribosylation of phage DNA in the escape context, and thereby restoring productive infection. file:BPT4/adfA/adfA-uniprot.txt Plays a role in counteracting the host DarT defense system. {ECO:0000250|UniProtKB:Q7Y5A4}. |
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Download this section (compressed HTML)Q: What is the three-dimensional structure of the AdfA-DarT complex, and how does the polymorphism at residue 164 (His in T4 vs Arg in wild-type RB69) control allele-specific binding to DarT1 versus DarT2?
Q: Against which natural bacterial DarTG variants is T4 AdfA essential when the NADAR-family glycohydrolase AdfN is absent or insufficient?
Experiment: Determine the crystal or cryo-EM structure of T4 AdfA and RB69 AdfA(R164H) bound to Escherichia coli DarT1 to define the toxin-neutralizing interface and the structural role of His164.
Experiment: Measure binding affinities (Kd) and in vitro inhibition constants (Ki) of purified T4 AdfA against a panel of diverse bacterial DarT toxins using isothermal titration calorimetry and ssDNA ADP-ribosylation assays.
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