| Claim | Evidence summary | Key sources with publication year | DOI URL |
|---|---|---|---|
| Identity / aliases | UniProt P17172 corresponds to Enterobacteria phage T4 gene product 27, commonly called **gp27**, also described as the **baseplate central spike complex protein**, **hub protein 27**, or central hub component of the T4 tail/baseplate; literature consistently places gp27 in the T4 baseplate central hub/spike rather than unrelated genes named “27” in other organisms. (pqac-00000003, pqac-00000005) | Arisaka et al. 2016; Yap et al. 2016 | https://doi.org/10.1007/s12551-016-0230-x ; https://doi.org/10.1073/pnas.1601654113 |
| Localization in virion | gp27 is localized at the **distal end of the tail tube / baseplate central hub**, where it forms part of the membrane-puncturing central spike device at the tail tip. It is not a soluble host-cell protein; its function is virion-associated and extracellular during adsorption/infection. (pqac-00000000, pqac-00000001, pqac-00000010) | Hu et al. 2015; Arisaka et al. 2016; Leprince & Mahillon 2023 | https://doi.org/10.1073/pnas.1501064112 ; https://doi.org/10.1007/s12551-016-0230-x ; https://doi.org/10.3390/v15010196 |
| Complex / stoichiometry | The central spike/hub is reported as **(gp27)3(gp5)3(gp5.4)1** or described equivalently as trimers of gp27 and gp5 terminated by a single gp5.4 needle. gp27 itself is a **trimer** of ~391 aa subunits. (pqac-00000001, pqac-00000003, pqac-00000006) | Arisaka et al. 2016 | https://doi.org/10.1007/s12551-016-0230-x |
| Interaction partners | Directly associated partners include **gp5** and **gp5.4** in the central spike, **gp6** in wedge-to-hub/baseplate assembly, and evidence also supports interaction with **gp28** in the central baseplate region. (pqac-00000005, pqac-00000012, pqac-00000004) | Yap et al. 2016; Arisaka et al. 2016 | https://doi.org/10.1073/pnas.1601654113 ; https://doi.org/10.1007/s12551-016-0230-x |
| Role in assembly | gp27 is a **hub nucleation/organizational protein** for baseplate assembly: six wedges assemble around the central hub, and tight **gp6–gp27** contacts are critical for forming the high-energy, dome-shaped baseplate. In the absence of gp27, gp6 assembles only into the low-energy star-shaped arrangement. (pqac-00000005, pqac-00000012, pqac-00000015) | Yap et al. 2016 | https://doi.org/10.1073/pnas.1601654113 |
| Role in infection initiation | gp27 is part of the **cell-puncturing device** that transmits conformational changes from receptor engagement/baseplate rearrangement to tail contraction and membrane penetration. During infection, the spike complex includes gp27 with gp5/gp5C and gp5.4; gp5C and likely gp5.4 dissociate upon outer-membrane penetration, exposing gp5* lysozyme activity in the periplasm. (pqac-00000000, pqac-00000009, pqac-00000010) | Hu et al. 2015; Leprince & Mahillon 2023 | https://doi.org/10.1073/pnas.1501064112 ; https://doi.org/10.3390/v15010196 |
| Enzymatic activity evidence (gp27 vs gp5*) | Available structural/functional evidence supports **no demonstrated peptidase or lysozyme activity for gp27 itself**. The **enzymatic activity in the spike complex belongs to gp5***, the N-terminal cleavage product of gp5, which has **lysozyme/peptidoglycan-degrading activity**; gp5 is cleaved at **Ser351–Ala352**. The peptidase-like domain annotations for gp27 therefore appear best interpreted as structural/evolutionary homology rather than proven catalysis in T4 gp27. (pqac-00000000, pqac-00000001, pqac-00000013) | Hu et al. 2015; Arisaka et al. 2016; Fokine & Rossmann 2016 | https://doi.org/10.1073/pnas.1501064112 ; https://doi.org/10.1007/s12551-016-0230-x ; https://doi.org/10.1016/j.str.2016.08.013 |
| Key quantitative data | T4 baseplate size estimates include **~3.3 MDa** for the in vitro-assembled hubless baseplate and **~6–6.5 MDa** for the complete baseplate; diameter is about **490 Å** and total protein count about **134–145 subunits/proteins** depending on assembly definition. High-resolution structural data cited for T4 baseplate/tail include **~4.2 Å crystallography** and **3.8 Å cryo-EM**; recent comparison systems include E217 whole virion maps at **3.1 Å** (extended) and **4.5 Å** (contracted), illustrating continued relevance of T4 gp27-like architecture in 2023 structural biology. (pqac-00000003, pqac-00000005, pqac-00000007) | Arisaka et al. 2016; Yap et al. 2016; Li et al. 2023 | https://doi.org/10.1007/s12551-016-0230-x ; https://doi.org/10.1073/pnas.1601654113 ; https://doi.org/10.1038/s41467-023-39756-z |


*Table: This table summarizes the main functional-annotation facts for Enterobacteria phage T4 gp27 (UniProt P17172), including identity, localization, interactions, assembly role, infection role, catalytic evidence, and quantitative structural data. It is useful as a compact evidence map for distinguishing experimentally supported functions from inferred domain annotations.*