Baseplate central hub and cell-puncturing complex protein gp27 of bacteriophage T4 that forms a hollow homotrimeric cylinder at the center of the tail baseplate. Because each gp27 subunit contains two homologous torus domains, the (gp27)3 trimer acts as a symmetry adaptor bridging the three-fold symmetric (gp5)3 membrane-puncturing lysozyme needle at its base with the six-fold symmetric inner baseplate wedges (gp6, gp25, gp53) and the hexameric gp48 tail-tube junction ring above, while forming a continuous central channel for viral DNA ejection.
| GO Term | Evidence | Action | Reason |
|---|---|---|---|
| GO:0098003 viral tail assembly | IEA GO_REF:0000043 | ACCEPT | Reason: gp27 forms the central baseplate hub cylinder around which the six peripheral baseplate wedges circularize and onto which the gp48/gp54 tail-tube junction rings assemble during T4 tail morphogenesis. Supporting Evidence: file:BPT4/27/27-uniprot.txt FUNCTION: Baseplate central spike complex-associated protein involved in the tail assembly. file:BPT4/27/27-deep-research-falcon.md gp27 provides the central hub scaffold around which the six baseplate wedges assemble, largely through key contacts with gp6. |
| GO:0098015 virus tail | IEA GO_REF:0000043 | MODIFY | Reason: gp27 is specifically localized to the central hub of the tail baseplate rather than an unspecified region of the virus tail; the more specific child term GO:0098025 (virus tail, baseplate) is already annotated and directly supported. Proposed replacements: virus tail, baseplate Supporting Evidence: PMID:11823865 A complex of gene product (gp) 5 (63K) and gp27 (44K), the central part of the baseplate, is required to penetrate the outer cell membrane of Escherichia coli and to disrupt the intermembrane peptidoglycan layer, promoting subsequent entry of phage DNA into the host. |
| GO:0098025 virus tail, baseplate | IEA GO_REF:0000120 | ACCEPT | Reason: gp27 is the central hub cylinder of the bacteriophage T4 tail baseplate, forming the (gp5-gp27)3 cell-puncturing complex at the center of the baseplate dome. Supporting Evidence: PMID:11823865 A complex of gene product (gp) 5 (63K) and gp27 (44K), the central part of the baseplate, is required to penetrate the outer cell membrane of Escherichia coli and to disrupt the intermembrane peptidoglycan layer, promoting subsequent entry of phage DNA into the host. file:BPT4/27/27-uniprot.txt Part of the baseplate macromolecular complex which consists of gp5, gp5.4, gp27 (central spike complex); gp6, gp25, gp53 (inner baseplate); gp7, gp8 (intermediate baseplate); gp9, gp10, gp11, gp12 (peripheral); gp48 and gp54 (proximal region of the tail tube) |
| GO:0005515 protein binding | IPI PMID:11823865 Structure of the cell-puncturing device of bacteriophage T4. | MODIFY | Reason: While the 2.9 A crystal structure of the (gp5-gp27)3 complex demonstrates direct stoichiometric binding between the gp27 trimer and the N-terminal beta-barrel domain of gp5, protein binding is overly general; gp27 functions specifically as a structural subunit of the virion baseplate hub (GO:0039660, structural constituent of virion). Proposed replacements: structural constituent of virion Supporting Evidence: PMID:11823865 The amino-terminal, antiparallel beta-barrel domain of gp5 is inserted into a cylinder formed by three gp27 monomers, which may serve as a channel for DNA ejection. |
| GO:0005515 protein binding | IPI PMID:15701513 Control of bacteriophage T4 tail lysozyme activity during th... | MODIFY | Reason: Co-crystallization of the gp5(S351L)-gp27 complex confirms physical interaction between gp27 and gp5, but protein binding is overly general; gp27 serves specifically as a structural component of the virion baseplate hub (GO:0039660, structural constituent of virion). Proposed replacements: structural constituent of virion Supporting Evidence: PMID:15701513 The crystal structure of the non-cleavage phenotype mutant of gp5, S351L, complexed with gene product 27, showed that the 18 residues in the vicinity of the potential cleavage site (disordered in the wild-type structure) had visible electron density. |
| GO:0098015 virus tail | IDA PMID:15701513 Control of bacteriophage T4 tail lysozyme activity during th... | MODIFY | Reason: gp27 is specifically a structural component of the tail baseplate hub complex with gp5; replacing GO:0098015 (virus tail) with the more specific child term GO:0098025 (virus tail, baseplate) matches its established localization. Proposed replacements: virus tail, baseplate Supporting Evidence: PMID:11823865 A complex of gene product (gp) 5 (63K) and gp27 (44K), the central part of the baseplate, is required to penetrate the outer cell membrane of Escherichia coli and to disrupt the intermembrane peptidoglycan layer, promoting subsequent entry of phage DNA into the host. PMID:15701513 The crystal structure of the non-cleavage phenotype mutant of gp5, S351L, complexed with gene product 27, showed that the 18 residues in the vicinity of the potential cleavage site (disordered in the wild-type structure) had visible electron density. |
| GO:0098025 virus tail, baseplate | IDA PMID:27193680 Structure of the T4 baseplate and its function in triggering... | ACCEPT | Reason: Atomic-resolution cryo-EM reconstructions of the 6-MDa T4 baseplate directly resolve the (gp27)3 central hub cylinder and its contacts with the surrounding baseplate wedge and tube-junction proteins. 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:BPT4/27/27-uniprot.txt Heteromultimer with gp5 trimer and gp5.4 monomer; this interaction forms the tail lysozyme complex that creates an extension of the tail tube (PubMed:12837775, PubMed:27193680). |
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Download this section (compressed HTML)Q: At what precise moment during sheath contraction and outer membrane penetration does the (gp27)3 cylinder dissociate from the gp5 C-terminal needle or from the distal tip of the gp48 tail-tube ring to clear the conduit for genomic DNA exit?
Q: How does the transient association of gp28 with gp27 during early morphogenesis promote assembly of the (gp5-gp27)3 hub complex prior to wedge circularization?
Experiment: Use cryo-electron tomography of bacteriophage T4 particles adsorbed to Escherichia coli minicells at sequential time points to determine whether the (gp27)3 cylinder remains attached to the gp48 tube tip in the periplasm or is released into the host envelope after outer membrane puncture.
Experiment: Co-express gp27 with candidate hub assembly factors gp26, gp28, and gp51 in Escherichia coli and analyze complex formation by size-exclusion chromatography coupled to multi-angle light scattering (SEC-MALS) to test whether gp28 stabilizes monomeric or trimeric gp27 intermediates.
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