Baseplate tail-tube junction protein gp48 of bacteriophage T4 that assembles as a homohexameric ring directly atop the central (gp27)3 hub cylinder to form the first annulus of the tail tube continuation within the baseplate dome. Together with the overlying gp54 hexameric ring, gp48 completes baseplate morphogenesis, interacts with inner baseplate wedge proteins (gp6, gp25, gp53), and creates the structural platform required to initiate polymerization of the gp19 tail tube.
| GO Term | Evidence | Action | Reason |
|---|---|---|---|
| GO:0098003 viral tail assembly | IEA GO_REF:0000043 | ACCEPT | Reason: gp48 forms a homohexameric ring at the top of the baseplate dome that, together with gp54, completes baseplate assembly and provides the mandatory initiation platform for polymerization of the gp19 tail tube. Supporting Evidence: file:BPT4/48/48-uniprot.txt Morphogenesis of the baseplate is completed by association of gp48 and gp54, which bind the upper part of the baseplate dome to form the platform for polymerization of the tail tube. file:BPT4/48/48-deep-research-falcon.md In T4, gp48 and gp54 are classically described as tube initiator proteins: structural components added late in baseplate assembly that create the platform from which the major tail tube protein gp19 polymerizes to form the tail tube. |
| GO:0098015 virus tail | IEA GO_REF:0000043 | MODIFY | Reason: gp48 is specifically localized to the baseplate-tail tube junction of the tail baseplate; the more specific child term GO:0098025 (virus tail, baseplate) is already annotated and supported by atomic-resolution cryo-EM data. Proposed replacements: virus tail, baseplate Supporting Evidence: file:BPT4/48/48-uniprot.txt Baseplate protein that forms, together with gp54, the baseplate-tail tube junction. The tail tube first 2 annuli are formed by gp48 and gp54, which are in continuation of the spike complex. |
| GO:0098025 virus tail, baseplate | IEA GO_REF:0000043 | ACCEPT | Reason: gp48 is an integral structural component of the bacteriophage T4 baseplate, forming the first hexameric annulus atop the central gp27 hub cylinder at the baseplate-tail tube junction. Supporting Evidence: file:BPT4/48/48-uniprot.txt Baseplate protein that forms, together with gp54, the baseplate-tail tube junction. The tail tube first 2 annuli are formed by gp48 and gp54, which are in continuation of the spike complex. file:BPT4/48/48-deep-research-falcon.md A key functional role is that a partially assembled baseplate cannot initiate tube formation until six copies each of gp48 and gp54 are added; after gp54 addition, 144 monomers of gp19 polymerize to form the tail tube in the classical assembly model. |
| GO:0098025 virus tail, baseplate | IDA PMID:27193680 Structure of the T4 baseplate and its function in triggering... | ACCEPT | Reason: Atomic cryo-EM reconstructions of the 6-MDa T4 baseplate resolve the homohexameric gp48 ring at the baseplate-tail tube junction directly above the (gp27)3 hub. 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:BPT4/48/48-uniprot.txt Homohexamer (PubMed:27193680). The tube first annulus is composed of a gp48 hexameric ring. Interacts with gp54. |
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Download this section (compressed HTML)Q: What is the functional role of the large peripheral/outer domain of gp48 that extends beyond its conserved tail-tube-like beta-barrel ring core at the baseplate dome?
Q: How do the contacts between gp48 and the inner baseplate wedge proteins (gp6, gp25, and gp53) remodel when the wedges splay outward during the dome-to-star conformational transition?
Experiment: Perform structure-guided mutagenesis of the interface between gp48 and the (gp27)3 pseudo-hexameric ring and between gp48 and gp25/gp53 to distinguish mutations that block baseplate assembly from those that uncouple baseplate expansion from tail tube penetration.
Experiment: Reconstitute the minimal gp27–gp48–gp54–gp19 assembly cascade in vitro using purified recombinant oligomers to measure the cooperative binding affinities governing sequential ring addition.
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