Intermediate baseplate wedge protein (gp8) of bacteriophage T4 that assembles as a homodimer (12 copies per virion; one dimer per wedge) within each of the six baseplate wedges. During sequential wedge morphogenesis, the gp8 homodimer binds to the (gp10)3-gp7 initiation complex and clamps a stretched inter-domain linker of gp7, reducing conformational flexibility and orienting gp7 to enable productive binding and folding of the gp6 dimer and completion of the baseplate wedge.
| GO Term | Evidence | Action | Reason |
|---|---|---|---|
| GO:0098003 viral tail assembly | IEA GO_REF:0000043 | ACCEPT | Summary: Automated keyword annotation accurately reflects the essential role of gp8 in sequential baseplate wedge morphogenesis. Reason: Binding of the gp8 homodimer to the (gp10)3-gp7 intermediate stabilizes a stretched gp7 linker and is strictly required before gp6, gp53, and gp25 can incorporate into the baseplate wedge. Supporting Evidence: file:BPT4/8/8-uniprot.txt Intermediate baseplate protein. Involved in the tail assembly. file:BPT4/8/8-deep-research-falcon.md A central mechanistic insight is that gp8 acts as a stabilizing wedge component by binding a gp7 linker that is stretched upon earlier assembly steps, thereby reducing gp7 flexibility and allowing gp6 to bind in a productive orientation to complete wedge assembly. |
| 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, gp8 localizes specifically to the intermediate wedge region of the baseplate (GO:0098025). Proposed replacements: virus tail, baseplate Supporting Evidence: file:BPT4/8/8-uniprot.txt Intermediate baseplate protein. Involved in the tail assembly. file:BPT4/8/8-deep-research-falcon.md A central mechanistic insight is that gp8 acts as a stabilizing wedge component by binding a gp7 linker that is stretched upon earlier assembly steps, thereby reducing gp7 flexibility and allowing gp6 to bind in a productive orientation to complete wedge assembly. |
| GO:0098025 virus tail, baseplate | IEA GO_REF:0000043 | ACCEPT | Summary: Automated keyword annotation accurately places gp8 in the viral tail baseplate. Reason: Six gp8 homodimers (12 monomers) are integral structural components of the six wedges of the bacteriophage T4 baseplate. Supporting Evidence: file:BPT4/8/8-uniprot.txt Note=Present in 12 copies in the baseplate. file:BPT4/8/8-deep-research-falcon.md A central mechanistic insight is that gp8 acts as a stabilizing wedge component by binding a gp7 linker that is stretched upon earlier assembly steps, thereby reducing gp7 flexibility and allowing gp6 to bind in a productive orientation to complete wedge assembly. |
| 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 gp8 homodimers bound to gp7 in the intermediate baseplate wedges. Reason: Taylor et al. (2016) resolved the atomic structure of the gp8 homodimer in complex with gp7 within the intact baseplate in both pre- and post-attachment conformations. 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:BPT4/8/8-uniprot.txt Homodimer (PubMed:19896486, PubMed:2403438, PubMed:27193680). Interacts with gp7. file:BPT4/8/8-deep-research-falcon.md A central mechanistic insight is that gp8 acts as a stabilizing wedge component by binding a gp7 linker that is stretched upon earlier assembly steps, thereby reducing gp7 flexibility and allowing gp6 to bind in a productive orientation to complete wedge assembly. |
| GO:0039660 structural constituent of virion | IDA PMID:27193680 Structure of the T4 baseplate and its function in triggering... | NEW | Summary: Six gp8 homodimers (12 subunits) serve as structural clamps on the six baseplate wedges in the mature bacteriophage T4 virion. Reason: Atomic-resolution cryo-EM reconstructions of the T4 baseplate (PMID:27193680) and X-ray crystal structures demonstrate that gp8 is a permanent structural component of the intermediate baseplate wedge that clamps a stretched inter-domain linker of 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:BPT4/8/8-uniprot.txt Intermediate baseplate protein. Involved in the tail assembly. |
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Download this section (compressed HTML)Q: Does gp8 make any direct transient contacts with gp6 during recruitment of the gp6 dimer to the (gp10)3-gp7-gp8 complex, or is its role in enabling gp6 incorporation mediated purely allosterically through clamping of the gp7 linker?
Suggested experts: Fumio Arisaka, Petr G. Leiman
Q: Why is gp8 dispensable in minimal contractile injection systems (such as R-type pyocins and Vibrio phage XM1) that retain gp6-, gp7-, and gp25-like core wedge homologs?
Suggested experts: Petr G. Leiman, Nicholas M. I. Taylor
Experiment: Perform hydrogen-deuterium exchange mass spectrometry (HDX-MS) on purified (gp10)3-gp7 complexes before and after addition of the gp8 homodimer, followed by addition of gp6.
Hypothesis: Binding of the gp8 dimer strongly protects the stretched inter-domain linker of gp7 and allosterically orders the gp6-binding alpha-helix of gp7 without requiring extensive direct gp8-gp6 contact surfaces.
Type: Hydrogen-deuterium exchange mass spectrometry (HDX-MS)
Experiment: Design a chimeric gp7 variant in which the gp8-binding linker region is replaced by a shorter, conformationally rigid linker modeled on minimal gp8-less myovirus baseplates, and test whether (gp10)3-gp7 can recruit gp6 in vitro in the absence of gp8.
Hypothesis: Shortening and rigidifying the gp7 inter-domain linker will bypass the requirement for gp8 clamping to allow direct (gp6)2-gp7 heterotrimer formation.
Type: Protein engineering and in vitro wedge reconstitution assay
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