Peripheral baseplate socket protein (gp9) of bacteriophage T4 that assembles as a homotrimer (18 copies per virion; six trimers per baseplate) and anchors the six long tail fibers to the baseplate periphery. Its C-terminal beta-barrel domain binds to baseplate wedge protein gp7, while its flexible N-terminal coiled-coil domain binds the proximal gp34 subunit of the long tail fiber. Together with the gp11-gp12 complex, gp9 stabilizes the metastable dome-shaped conformation of the pre-infection baseplate and swivels upon host receptor engagement by the long tail fibers to transmit the mechanical signal that initiates the dome-to-star transition and tail sheath contraction.
| GO Term | Evidence | Action | Reason |
|---|---|---|---|
| GO:0019076 viral release from host cell | IEA GO_REF:0000002 | REMOVE | Summary: Spurious InterPro2GO mapping that misassigns a baseplate tail-fiber socket protein to viral release from the host cell. Reason: gp9 is a structural component of the extracellular virion baseplate that connects the long tail fibers and transmits the receptor-binding signal for tail sheath contraction during host entry; it plays no role in host cell lysis or viral egress. Supporting Evidence: file:BPT4/9/9-uniprot.txt Peripheral baseplate protein that is part of the tail fiber network (PubMed:10545330, PubMed:27193680). Connects the long tail fibers to the baseplate and, after virus attachment to a host cell, probably changes its conformation to trigger the signal for tail contraction (PubMed:10545330). Involved in the tail assembly (PubMed:21129200). file:BPT4/9/9-deep-research-falcon.md gp9 forms the **attachment/socket point for the long tail fibers (LTFs)** on the baseplate |
| GO:0098003 viral tail assembly | IEA GO_REF:0000043 | ACCEPT | Summary: Automated keyword annotation accurately captures the role of gp9 in baseplate stabilization and long tail fiber attachment during tail morphogenesis. Reason: During tail assembly, gp9 trimers bind to the peripheral gp7 domains of the assembled baseplate to stabilize the dome-shaped baseplate and serve as the socket for long tail fiber attachment. Supporting Evidence: file:BPT4/9/9-uniprot.txt Peripheral baseplate protein that is part of the tail fiber network (PubMed:10545330, PubMed:27193680). Connects the long tail fibers to the baseplate and, after virus attachment to a host cell, probably changes its conformation to trigger the signal for tail contraction (PubMed:10545330). Involved in the tail assembly (PubMed:21129200). file:BPT4/9/9-deep-research-falcon.md Pulse-chase analysis indicates **gp9 attaches after wedge assembly**, and this is followed by the simultaneous attachment of **gp11** and the **short tail fibers (gp12)**; together, gp9 and the gp11–gp12 complex stabilize the **dome-shaped baseplate** configuration |
| GO:0098015 virus tail | IEA GO_REF:0000043 | MODIFY | Summary: Correct parent cellular component term that should be refined to the baseplate subcompartment. Reason: Within the virion tail, gp9 localizes specifically to the peripheral rim of the baseplate (GO:0098025). Proposed replacements: virus tail, baseplate Supporting Evidence: file:BPT4/9/9-uniprot.txt The C-terminus is bound to the baseplate, and the N-terminus coiled-coil domain is associated with the long tail fibers. file:BPT4/9/9-deep-research-falcon.md gp9 forms the **attachment/socket point for the long tail fibers (LTFs)** on the baseplate |
| GO:0098025 virus tail, baseplate | IEA GO_REF:0000043 | ACCEPT | Summary: Automated keyword annotation accurately places gp9 in the viral tail baseplate. Reason: Six gp9 homotrimers are anchored to the peripheral rim of the bacteriophage T4 baseplate. Supporting Evidence: file:BPT4/9/9-uniprot.txt Peripheral baseplate protein that is part of the tail fiber network (PubMed:10545330, PubMed:27193680). Connects the long tail fibers to the baseplate and, after virus attachment to a host cell, probably changes its conformation to trigger the signal for tail contraction (PubMed:10545330). Involved in the tail assembly (PubMed:21129200). file:BPT4/9/9-deep-research-falcon.md gp9 forms the **attachment/socket point for the long tail fibers (LTFs)** on the baseplate |
| GO:0098025 virus tail, baseplate | IDA PMID:27193680 Structure of the T4 baseplate and its function in triggering... | ACCEPT | Summary: Near-atomic cryo-EM structures of the T4 baseplate directly resolve the six gp9 homotrimers bound to gp7 at the baseplate periphery. Reason: Taylor et al. (2016) resolved the atomic structure and swiveling motion of the gp9 trimers attached to the peripheral domains of gp7 in pre- and post-attachment baseplate states. 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:BPT4/9/9-uniprot.txt Homotrimer (PubMed:27193680). The gp9 trimer interacts with the long tail fiber (LTF) that comprises gp34 trimer, gp35, gp36 and a gp37 trimer. file:BPT4/9/9-deep-research-falcon.md gp9 forms the **attachment/socket point for the long tail fibers (LTFs)** on the baseplate |
| GO:0039660 structural constituent of virion | IDA PMID:27193680 Structure of the T4 baseplate and its function in triggering... | NEW | Summary: Six gp9 homotrimers (18 subunits) form the structural sockets on the upper peripheral rim of the baseplate that anchor the six long tail fibers to the virion. Reason: Atomic cryo-EM reconstructions of the T4 baseplate (PMID:27193680) establish that gp9 is an integral structural constituent of the virion baseplate periphery that physically links the proximal gp34 trimer of each long tail fiber to gp7. 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:BPT4/9/9-uniprot.txt Peripheral baseplate protein that is part of the tail fiber network (PubMed:10545330, PubMed:27193680). Connects the long tail fibers to the baseplate and, after virus attachment to a host cell, probably changes its conformation to trigger the signal for tail contraction (PubMed:10545330). Involved in the tail assembly (PubMed:21129200). |
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Download this section (compressed HTML)Q: How many long tail fibers must simultaneously engage host receptors and apply torque through their gp9 sockets to overcome the activation barrier for the cooperative dome-to-star transition of the baseplate?
Suggested experts: Petr G. Leiman, Michael G. Rossmann, Fumio Arisaka
Q: What is the precise atomic interface between the N-terminal coiled-coil domain of the gp9 trimer and the N-terminal baseplate-binding domain of the gp34 proximal long tail fiber trimer?
Suggested experts: Petr G. Leiman, Mark J. van Raaij
Experiment: Determine the high-resolution cryo-EM structure of the isolated gp9 homotrimer bound to the N-terminal fragment of the gp34 homotrimer using focused local refinement.
Hypothesis: The N-terminal coiled-coil of gp9 forms a symmetry-matched three-fold helical bundle clasp with the N-terminal domain of gp34 that permits wide-angle swiveling without dissociation under mechanical load.
Type: Single-particle cryo-EM with focused local refinement
Experiment: Use optical tweezers to apply controlled piconewton pulling forces to individual long tail fibers on immobilized T4 virions while monitoring baseplate dome-to-star transition and sheath contraction.
Hypothesis: Mechanical deflection of at least three gp9 sockets beyond a critical angular threshold cooperatively destabilizes the dome-shaped gp7-gp10 network to trigger short tail fiber unpinning.
Type: Single-molecule optical tweezers force spectroscopy
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