| Topic/claim | Evidence summary | Evidence type (genetics/EM/biochemistry/cryo-EM/review) | Key source (author, year, journal) | Publication date | URL | What it implies for gp28 function/localization | Notes/uncertainties |
|---|---|---|---|---|---|---|---|
| T4 gene 28 is required for central baseplate hub/plug morphogenesis | In T4 group II mutant lysates, gene 28-defective phage accumulated normal 15S arm precursors but only small amounts of unstable 70S sixfold-symmetric baseplate-like structures that lacked density at the center; authors concluded group II products contribute to formation of the central plug/hub of the baseplate. | genetics/EM/biochemistry | Kikuchi & King, 1975, *Journal of Molecular Biology* | Dec 1975 | https://doi.org/10.1016/S0022-2836(75)80179-3 | Strongest direct experimental evidence that gp28 functions in assembly of the central baseplate region rather than in wedge/arm formation; localization inferred to central hub/plug region. (pqac-00000000, pqac-00000008, pqac-00000009) | Does not resolve exact subunit number, atomic structure, or whether gp28 remains in the mature virion. |
| gp28 is one of six proteins required for T4 hub assembly; gp27-gp28 interaction has been reported | Review of T4 tail/baseplate assembly states that gp5, gp27, gp26, gp28, gp51 and gp29 are required for hub formation; it also cites earlier work describing gp28 as a constituent of the central baseplate part and reporting evidence for interaction between gp27 and gp28. | review/biochemistry | Arisaka et al., 2016, *Biophysical Reviews* | Nov 2016 | https://doi.org/10.1007/s12551-016-0230-x | Supports assignment of gp28 to the hub/central baseplate assembly pathway and suggests a direct or near-direct relationship with gp27 during hub morphogenesis. (pqac-00000002, pqac-00000004, pqac-00000005) | Review explicitly notes gp26/gp28 location and specific functions remained unknown in T4 at that time. |
| gp28 stoichiometry and precise localization in T4 remain unresolved | Stoichiometry review states that neither the localization nor the number of gp26 and gp28 molecules per baseplate had been determined; it also cites evidence that co-expression of gene 27 with gp28 caused gp27 to appear in the membrane fraction, consistent with gp27-gp28 association in a heterologous/fractionation assay. | review/biochemistry | Arisaka, 2012, InTech chapter / arXiv record | Mar 2012 | https://doi.org/10.5772/35125 | Indicates gp28 is functionally linked to hub proteins but remains poorly localized experimentally in mature T4 particles; interaction with gp27 is plausible but indirect for virion placement. (pqac-00000001) | Secondary-source synthesis; membrane-fractionation evidence is suggestive, not a high-resolution virion structure. |
| gp28 may function transiently as an assembly chaperone rather than a permanent mature-particle component | Modern tail-structure review proposes that T4 gp26 and gp28 likely perform a chaperone function because they are not found in the fully assembled baseplate-tube complex. | review | Bhatt et al., 2021, *Tail Structure and Dynamics* (Elsevier chapter DOI record) | Jan 2021 | https://doi.org/10.1016/B978-0-12-809633-8.20965-5 | Offers a mechanistic interpretation that reconciles older genetics showing essential assembly function with persistent uncertainty about mature-particle localization. (pqac-00000011) | This is a hypothesis/synthesis, not direct structural proof for T4 gp28 itself. |
| A gp28-like protein in another contractile phage can occupy the baseplate-sheath interface and initiate sheath attachment | In *Agrobacterium* phage Milano, BW1 annotated as gp28 was placed by cryo-EM at the top of the baseplate wedge; its fold resembles the sheath handshaker domain, it accepts the N- and C-terminal arms of the first sheath layer, and it forms a disulfide-linked interface with the tailspike (including Cys41 of BW1). | cryo-EM | Sonani et al., 2024, *Nature Communications* | Jan 2024 | https://doi.org/10.1038/s41467-024-44959-z | Comparative evidence suggests one plausible evolutionary role for gp28-family proteins is as an adaptor/scaffold linking baseplate, sheath initiation, and receptor-binding structures. (pqac-00000010, pqac-00000012, pqac-00000013) | This is a homolog/comparative system, not direct evidence for T4 gp28; nomenclature similarity does not guarantee identical placement in T4. |
| Contractile-tail baseplate/hub knowledge is being used for precision antibacterial engineering | Engineered diffocin targeting *Clostridioides difficile* was resolved in pre- and post-contraction states with high-resolution cryo-EM; authors emphasize design principles for “potent protein-based precision antibiotics.” The study also cites major disease burden, with nearly 250,000 hospitalizations and 13,000 deaths per year in the US. | cryo-EM/application | Cai et al., 2024, *Nature Communications* | Aug 2024 | https://doi.org/10.1038/s41467-024-51038-w | While not about T4 gp28 directly, it demonstrates how structural understanding of contractile-tail baseplates and hubs can be translated into programmable antibacterial systems. (pqac-00000014, pqac-00000016, pqac-00000018) | Application is to an engineered bacteriocin/CIS rather than T4; relevance is conceptual and translational. |
| Structural atlases of therapeutic phages enable baseplate-guided phage engineering | 2024 cryo-EM/proteomics study of therapeutic *Pseudomonas* phage Pa193 built atomic models for 21 structural polypeptides, visualized ~500 Å tail fibers, and resolved the interface between baseplate and tail fibers; authors frame the work as supporting phage therapy and engineering opportunities. | cryo-EM/application | Iglesias et al., 2024, *Communications Biology* | Oct 2024 | https://doi.org/10.1038/s42003-024-06985-x | Shows current real-world implementation of structural baseplate research: mapping interfaces that control adsorption and host targeting for therapeutic phage development. (pqac-00000019, pqac-00000020) | Not specific to T4 gp28; useful as current-state context for how analogous baseplate proteins are studied and exploited. |


*Table: This table compiles the main evidence supporting functional annotation of Enterobacteria phage T4 gp28 and places it in the context of recent comparative structural and application-focused studies. It highlights what is known directly from T4 experiments, what remains unresolved, and how newer phage/CIS structures inform interpretation.*