Short tail fiber protein gp12 is a 527-residue homotrimeric adhesin and structural fiber protein (18 copies per virion) that forms the six short tail fibers of bacteriophage T4. Each gp12 trimer comprises an N-terminal baseplate-binding domain anchored to gp10, an elongated intertwined beta-helical shaft clamped at its central hinge by gp11, and a C-terminal receptor-binding head domain stabilized by an octahedrally coordinated zinc ion (bound by His445 and His447 from each protomer). Stowed in a compact garland beneath the dome-shaped baseplate prior to infection, gp12 unfolds downward during the dome-to-star baseplate transition to bind irreversibly to the core lipopolysaccharide region of Escherichia coli, locking the virion onto the host cell surface for tail sheath contraction and DNA injection.
| GO Term | Evidence | Action | Reason |
|---|---|---|---|
| GO:0019062 virion attachment to host cell | IEA GO_REF:0000043 | MODIFY | Summary: gp12 mediates irreversible virion attachment to the host cell, but this term is less specific than entry receptor-mediated virion attachment to host cell (GO:0098670). Reason: While gp12 functions in virion attachment, biochemical and structural evidence shows that its C-terminal head domain specifically recognizes and binds irreversibly to the core lipopolysaccharide (LPS) receptor on the Escherichia coli outer membrane. Modifying this broad term to GO:0098670 (entry receptor-mediated virion attachment to host cell), which is already present on this gene, captures the specific mechanism. Proposed replacements: entry receptor-mediated virion attachment to host cell Supporting Evidence: file:BPT4/12/12-uniprot.txt Structural component of the short tail fiber. Adhesion protein that binds irreversibly to the lipopolysaccharides component (LPS) on the cell surface of Escherichia coli B strains during virus attachment. After at least three long tail fibers have bound, short tail fibers extend and bind irreversibly to the core region of the host cell LPS. file:BPT4/12/12-deep-research-falcon.md **gp12 forms the short tail fibers of bacteriophage T4 and mediates irreversible binding to the host** by binding the **core region of Escherichia coli LPS**. |
| GO:0046718 symbiont entry into host cell | IEA GO_REF:0000043 | MODIFY | Summary: gp12 participates in the viral entry pathway solely by mediating irreversible receptor-mediated attachment of the baseplate to host lipopolysaccharide, which is more precisely represented by GO:0098670. Reason: GO:0046718 (symbiont entry into host cell) is an overly broad parent process derived from keyword mapping. The specific step performed by gp12 is irreversible binding of the deployed short tail fibers to the host LPS core receptor on the outer surface (GO:0098670, entry receptor-mediated virion attachment to host cell). Proposed replacements: entry receptor-mediated virion attachment to host cell Supporting Evidence: file:BPT4/12/12-uniprot.txt Structural component of the short tail fiber. Adhesion protein that binds irreversibly to the lipopolysaccharides component (LPS) on the cell surface of Escherichia coli B strains during virus attachment. After at least three long tail fibers have bound, short tail fibers extend and bind irreversibly to the core region of the host cell LPS. file:BPT4/12/12-deep-research-falcon.md **gp12 forms the short tail fibers of bacteriophage T4 and mediates irreversible binding to the host** by binding the **core region of Escherichia coli LPS**. |
| GO:0046872 metal ion binding | IEA GO_REF:0000002 | MODIFY | Summary: gp12 binds a structural metal ion at its trimer axis, which X-ray crystallography and X-ray absorption spectroscopy identify specifically as a zinc ion (Zn2+). Reason: High-resolution crystal structures of the gp12 C-terminal receptor-binding domain demonstrate that three monomers octahedrally coordinate a single buried Zn2+ ion via six histidine residues (His445 and His447 from each chain). Modifying general GO:0046872 (metal ion binding) to its specific descendant GO:0008270 (zinc ion binding) accurately reflects the experimental evidence. Proposed replacements: zinc ion binding Supporting Evidence: file:BPT4/12/12-deep-research-falcon.md The receptor-binding domain structure contains a **Zn2+ ion coordinated octahedrally by six histidines**—specifically **His445 and His447 from each monomer**—forming an unusual metal-binding site at the interface of receptor-binding subdomains. |
| GO:0098015 virus tail | IEA GO_REF:0000043 | MODIFY | Summary: gp12 is part of the bacteriophage T4 tail, but this term is too general compared to its specific localizations as the short tail fiber and peripheral component of the tail baseplate. Reason: gp12 forms the six short tail fibers (GO:0098024, virus tail, fiber) that are anchored to gp10 and gp11 and stowed within the peripheral garland of the tail baseplate (GO:0098025, virus tail, baseplate). Replacing the general parent term GO:0098015 with both specific subcompartment terms already present on this gene captures its full localization. Proposed replacements: virus tail, fiber virus tail, baseplate Supporting Evidence: file:BPT4/12/12-uniprot.txt Structural component of the short tail fiber. Adhesion protein that binds irreversibly to the lipopolysaccharides component (LPS) on the cell surface of Escherichia coli B strains during virus attachment. After at least three long tail fibers have bound, short tail fibers extend and bind irreversibly to the core region of the host cell LPS. file:BPT4/12/12-deep-research-falcon.md Structural reviews describe that gp12 N-termini attach to **gp10 trimers** in the baseplate, while **gp11 trimers** hold the short tail fibers at a hinge roughly halfway along the fiber—placing gp12 within a defined baseplate attachment/hinge architecture. |
| GO:0098024 virus tail, fiber | IEA GO_REF:0000120 | ACCEPT | Summary: gp12 homotrimers form the six short tail fibers of bacteriophage T4. Reason: Structural and biochemical studies establish that gp12 assembles into club-shaped ~52 nm homotrimeric short tail fibers that extend from the baseplate periphery during host attachment. Supporting Evidence: file:BPT4/12/12-uniprot.txt Structural component of the short tail fiber. Adhesion protein that binds irreversibly to the lipopolysaccharides component (LPS) on the cell surface of Escherichia coli B strains during virus attachment. After at least three long tail fibers have bound, short tail fibers extend and bind irreversibly to the core region of the host cell LPS. file:BPT4/12/12-deep-research-falcon.md **gp12 forms the short tail fibers of bacteriophage T4 and mediates irreversible binding to the host** by binding the **core region of Escherichia coli LPS**. |
| GO:0098670 entry receptor-mediated virion attachment to host cell | IEA GO_REF:0000043 | ACCEPT | Summary: Once unfolded from the baseplate, the C-terminal receptor-binding domain of the gp12 short tail fiber binds irreversibly to the core lipopolysaccharide (LPS) receptor on Escherichia coli. Reason: Extensive biochemical assays, LPS-binding inhibition experiments, and cryo-EM reconstructions of T4 attached to host cells demonstrate that gp12 is the primary adhesin responsible for irreversible receptor-mediated attachment to the host outer membrane LPS core. Supporting Evidence: file:BPT4/12/12-uniprot.txt Structural component of the short tail fiber. Adhesion protein that binds irreversibly to the lipopolysaccharides component (LPS) on the cell surface of Escherichia coli B strains during virus attachment. After at least three long tail fibers have bound, short tail fibers extend and bind irreversibly to the core region of the host cell LPS. file:BPT4/12/12-deep-research-falcon.md **gp12 forms the short tail fibers of bacteriophage T4 and mediates irreversible binding to the host** by binding the **core region of Escherichia coli LPS**. |
| GO:0098025 virus tail, baseplate | IDA PMID:27193680 Structure of the T4 baseplate and its function in triggering... | ACCEPT | Summary: Atomic structures of the T4 baseplate resolve the six gp12 homotrimers stowed in a peripheral garland beneath the dome-shaped baseplate and anchored via their N-termini and central hinges to baseplate wedge proteins gp10 and gp11. Reason: Direct cryo-EM and crystallographic reconstructions of the intact T4 baseplate (PMID:27193680) show that gp12 is an integral structural constituent of the pre-attachment baseplate dome and remains anchored to the baseplate periphery via gp10 and gp11 after deployment. Supporting Evidence: PMID:27193680 Here we present the atomic structure of the approximately 6-megadalton bacteriophage T4 baseplate in its pre- and post-host attachment states and explain the events that lead to sheath contraction in atomic detail. file:BPT4/12/12-uniprot.txt Homotrimer. {ECO:0000269|PubMed:11743729, ECO:0000269|PubMed:27193680}. file:BPT4/12/12-deep-research-falcon.md Structural reviews describe that gp12 N-termini attach to **gp10 trimers** in the baseplate, while **gp11 trimers** hold the short tail fibers at a hinge roughly halfway along the fiber—placing gp12 within a defined baseplate attachment/hinge architecture. |
| GO:0039660 structural constituent of virion | IDA PMID:27193680 Structure of the T4 baseplate and its function in triggering... | NEW | Summary: Six gp12 homotrimers (18 subunits) form the structural short tail fibers of the bacteriophage T4 virion, stowed as a garland beneath the pre-attachment baseplate and deployed upon host recognition. Reason: Atomic structures of the T4 baseplate (PMID:27193680) and crystallographic studies of gp12 establish that gp12 is a major structural component of the virion short tail fibers and baseplate periphery. Supporting Evidence: PMID:27193680 Here we present the atomic structure of the approximately 6-megadalton bacteriophage T4 baseplate in its pre- and post-host attachment states and explain the events that lead to sheath contraction in atomic detail. file:BPT4/12/12-uniprot.txt Structural component of the short tail fiber. Adhesion protein that binds irreversibly to the lipopolysaccharides component (LPS) on the cell surface of Escherichia coli B strains during virus attachment. After at least three long tail fibers have bound, short tail fibers extend and bind irreversibly to the core region of the host cell LPS. |
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Download this section (compressed HTML)Q: Does each gp12 homotrimer bind a single LPS core oligosaccharide along its C-terminal flat apex or three LPS molecules simultaneously across its threefold-symmetric lateral clefts in vivo?
Q: How does the cytoplasmic chaperone gp57A prevent off-pathway aggregation of the intertwined beta-stranded shaft domains of gp12 prior to octahedral Zn2+ capture at the C-terminus?
Experiment: Determine the cryo-EM or X-ray co-crystal structure of the gp12 C-terminal receptor-binding domain bound to purified Escherichia coli B core-lipid A oligosaccharide (Re/Rd/Rc chemotypes).
Hypothesis: The three symmetry-related surface pockets surrounding the C-terminal apex of the gp12 trimer each engage the inner-core heptose/Kdo sugars of LPS simultaneously, explaining the near-irreversible avidity of short tail fiber binding.
Experiment: Construct His445Ala and His447Ala substitutions in full-length gp12 co-expressed with gp57A and measure trimer assembly, protease resistance, and Zn2+ stoichiometry by ICP-MS.
Hypothesis: Octahedral coordination of Zn2+ by His445 and His447 acts as a C-terminal kinetic lock required to register and zip the three beta-helical chains during gp57A-assisted folding.
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