| Functional/structural role | Evidence type | Key quantitative details | Interaction partners | Key citations with year and DOI URL |
|---|---|---|---|---|
| gp6 ring / wedge architecture in the T4 baseplate | Cryo-EM + X-ray + structural fitting | Full-length gp6 is **660 aa**; **12 copies per tail / baseplate** arranged as **6 dimers** (**2 gp6 per wedge**); monomer mass **74.4 kDa**; gp6 is dimeric in solution and forms an inner ring around the hub that helps connect wedges and maintain baseplate integrity (pqac-00000003, pqac-00000007, pqac-00000011, pqac-00000016) | gp6–gp6, gp7, gp8, gp27/hub; in dome conformation also contacts gp5 (pqac-00000003, pqac-00000012, pqac-00000016) | Aksyuk et al. 2009, https://doi.org/10.1016/j.str.2009.04.005; Taylor et al. 2016, https://doi.org/10.1038/nature17971; Leiman et al. 2010, https://doi.org/10.1186/1743-422x-7-355 |
| Sequential wedge assembly and baseplate formation | Biochemistry / assembly reconstitution + analytical ultracentrifugation + review synthesis | Ordered pathway: **gp11 → gp10 → gp7 → gp8 → gp6 → gp53 → gp25**; wedge intermediate stoichiometry reported as **(gp10)3:(gp7)1:(gp8)2:(gp6)2 = 3:1:2:2**; complexes containing gp6 sediment at about **14.5S**, increasing to **15.0–15.3S** with gp53/gp25; gp53 binding can drive spontaneous star-like hubless baseplate assembly; star-like particle reported near **43S** (pqac-00000010, pqac-00000017, pqac-00000019) | gp10, gp7, gp8, gp53, gp25, gp11; gp8 acts as folding/assembly aid for gp6 (pqac-00000011, pqac-00000017, pqac-00000019) | Yap et al. 2010, https://doi.org/10.1002/mabi.201000042; Leiman et al. 2010, https://doi.org/10.1186/1743-422x-7-355; Arisaka 2012, https://doi.org/10.5772/35125 |
| “Hinge-pin” conformational switch and proposed trigger for sheath contraction | X-ray fragment structure fitted into cryo-EM maps; infection-state/baseplate transition models | gp6 N- and C-terminal regions preserve dimer interfaces but the hinge angle changes by about **15°**, producing about **10 Å** radial expansion of the gp6 ring during dome→star rearrangement; this repositions the N-terminal region that contacts the first gp18 sheath ring and is proposed to initiate contraction (pqac-00000014, pqac-00000023, pqac-00000025) | Signal transmission pathway described as **gp9 → gp10 → gp7 → gp6 → gp18**; N-terminus contacts gp18/gp25/gp53, C-terminus contacts gp7 and in dome also gp5/gp8; gp6–gp27 interaction is a critical nucleation step for the dome-shaped high-energy baseplate (pqac-00000012, pqac-00000014, pqac-00000016) | Aksyuk et al. 2009, https://doi.org/10.1016/j.str.2009.04.005; Yap et al. 2016, https://doi.org/10.1073/pnas.1601654113 |
| Domain architecture and key residues | X-ray crystallography of C-terminal fragments + cryo-EM segmentation | Crystallized fragments include **gp6_334C (residues 334–660)** and **gp6_306C (306–660)**; C-terminal half resolves **domain I (340–411)**, **β-barrel domain II (489–620)**, and **domain III (412–489 and 620–660)**; loop 1 in domain II spans **519–534** and contacts gp5; **Cys338** is the only cysteine and can form a disulfide-linked dimer in vitro; **C338S** was used to improve crystallization; gp6_334C crystals diffracted to **3.2 Å** (pqac-00000022, pqac-00000023, pqac-00000024, pqac-00000025) | gp5 (loop 1 contact), gp7, gp8, gp25, gp53, gp18 depending on domain/conformation (pqac-00000025, pqac-00000026) | Aksyuk et al. 2009, https://doi.org/10.1016/j.str.2009.04.005 |
| Conserved wedge module across contractile injection systems / T6SS-related systems | Comparative structural biology + cryo-EM + review | Taylor et al. interpret the **(gp6)2–gp7** unit as a likely conserved assembly intermediate across contractile injection systems; in Vibrio phage XM1, the **(gp16)2–gp17** wedge is explicitly described as homologous to T4 **(gp6)2–gp7**; recent CIS/baseplate studies use T4 gp6 as a reference/model for wedge architecture (pqac-00000009, pqac-00000027) | Conserved module centers on **(gp6)2–gp7**; related systems pair gp6-like wedge proteins with sheath initiators/hub proteins analogous to T4 gp25/gp27 modules (pqac-00000009, pqac-00000027) | Taylor et al. 2016, https://doi.org/10.1038/nature17971; Wang et al. 2023, https://doi.org/10.3390/v15081673 |
| Applications / engineering context informed by gp6-like wedge biology | Recent structural studies of antibacterial nanomachines | Direct application of T4 gp6 itself was not shown, but gp6-like wedge architecture informs engineering of contractile antibacterial devices. A 2024 diffocin study resolved structures at **2.2 Å** (pre-contraction) and **3.6 Å** (post-contraction), with **6 baseplate proteins** and **2 trunk proteins**, and frames these machines as “precision antibiotics”; curated particle counts included **1088 pre-contraction**, **742 transitional**, and **872 final post-contraction** collar-baseplate pairs. Tailocins/pyocins are also being retargeted by swapping tail fibers; one source notes up to **200 R-type pyocins per cell** can be released (pqac-00000028, pqac-00000029, pqac-00000030, pqac-00000031) | Engineered systems rely on baseplate/sheath/tail-fiber modules rather than isolated gp6; T4 gp6 serves as a structural paradigm for wedge organization and contraction logic (pqac-00000027, pqac-00000028, pqac-00000031) | Cai et al. 2024, https://doi.org/10.1038/s41467-024-51038-w; Wang et al. 2023, https://doi.org/10.3390/v15081673 |


*Table: This table summarizes the experimentally supported structural and functional annotation of Enterobacteria phage T4 gp6 (UniProt P19060), including assembly order, domain architecture, conformational triggering, conservation, and engineering relevance. It is designed to provide a compact evidence map linking specific mechanistic claims to quantitative details and citations.*