| Claim/annotation (function/process/localization) | Key experimental evidence (brief) | Quantitative/statistical data (if any) | Primary source(s) with year and URL |
|---|---|---|---|
| **Identity and core function:** gp57/gp57A is a **nonstructural tail-fiber assembly helper / molecular chaperone** in *Enterobacteria phage T4* rather than a virion structural component. | Primary biochemical/genetic studies identify gene 57 product as a helper absent from mature virions and required for tail fiber formation; reviews classify gp57A among T4 tail/fiber chaperones. (pqac-00000002, pqac-00000003, pqac-00000005) | Encoded product reported as **79 aa**; apparent SDS-PAGE size about **5.7–6 kDa**, despite higher calculated mass. (pqac-00000002, pqac-00000008, pqac-00000012) | Hashemolhosseini et al., 1996, J Bacteriol, https://doi.org/10.1128/jb.178.21.6258-6265.1996; Matsui et al., 1997, J Bacteriol, https://doi.org/10.1128/jb.179.6.1846-1851.1997; Leiman et al., 2010, Virol J, https://doi.org/10.1186/1743-422x-7-355 |
| **Substrates/targets:** gp57A assists folding/assembly of **gp12, gp34, and gp37**. | Table-based review annotation assigns gp57A to folding of gp12, gp34, gp37; structural/review papers state gp34 and gp37 require gp57 for proper trimeric assembly, and gp12 also depends on gp57. (pqac-00000005, pqac-00000004, pqac-00000012) | Long tail fiber is ~**70 nm** long; gp37 is ~**109 kDa** in review annotation; gp37 distal subunit is **1,026 aa** in helper-protein study. (pqac-00000012, pqac-00000011, pqac-00000019) | Bartual et al., 2010, PNAS, https://doi.org/10.1073/pnas.1011218107; Leiman et al., 2010, Virol J, https://doi.org/10.1186/1743-422x-7-355; Hashemolhosseini et al., 1996, J Bacteriol, https://doi.org/10.1128/jb.178.21.6258-6265.1996 |
| **Assembly pathway role:** gp57 acts at multiple discrete steps in long- and short-tail fiber morphogenesis. | Genetic analysis showed gp57 is required for **gp34 dimerization** (proximal half-fiber precursor), acts **before gp38** to promote **gp37 dimerization** (distal half-fiber precursor), and is needed for **gp12 incorporation** into the baseplate. (pqac-00000001, pqac-00000014) | Three distinct assembly reactions assigned to gp57 in classic genetic study. (pqac-00000001, pqac-00000014) | Herrmann & Wood, 1981/2004 record, Mol Gen Genet, https://doi.org/10.1007/bf00271208 |
| **Biochemical state:** gp57A is a small, highly **alpha-helical oligomer**, most directly supported as a **tetramer** in solution. | Sedimentation equilibrium and glutaraldehyde cross-linking supported a tetrameric native assembly; CD spectroscopy indicated strong alpha-helical character. Some later review/tabulation reports alternative oligomeric mixtures, but direct biochemical evidence most strongly supports tetramer. (pqac-00000009, pqac-00000008, pqac-00000012) | Monomer from sequence **8,481 Da**; native molecular weight **33,470 ± 4,780 Da**; CD estimate **~94% α-helix**. Review table also lists **trimer/hexamer/dodecamer** mixture. (pqac-00000009, pqac-00000012) | Matsui et al., 1997, J Bacteriol, https://doi.org/10.1128/jb.179.6.1846-1851.1997; Leiman et al., 2010, Virol J, https://doi.org/10.1186/1743-422x-7-355 |
| **Protein properties:** gp57A is unusually acidic and compositionally atypical. | Helper-protein characterization reported a highly acidic 79-residue protein lacking several common residues and forming intracellular quasi-crystalline fibers when overproduced. (pqac-00000002, pqac-00000011) | Excess of **9 negative charges**; lacks **Phe, Trp, Tyr, His, Pro, Cys**. Partial complementation seen with only the **N-terminal 25 aa** fragment. (pqac-00000011) | Hashemolhosseini et al., 1996, J Bacteriol, https://doi.org/10.1128/jb.178.21.6258-6265.1996 |
| **Effect of gp57A absence:** loss of gp57 prevents normal assembly of target tail-fiber proteins. | In the absence of p57, **p34, p37, and p12 remain unassembled**; for gp12 specifically, material partitions into cell debris/membrane rather than soluble/native trimeric form. (pqac-00000002, pqac-00000009, pqac-00000011) | Uninduced/plasmidless complementation controls gave low burst sizes versus induced gp57A expression: **167 PFU/cell** induced vs **3.3** and **0.05 PFU/cell** controls. (pqac-00000008) | Hashemolhosseini et al., 1996, J Bacteriol, https://doi.org/10.1128/jb.178.21.6258-6265.1996; Matsui et al., 1997, J Bacteriol, https://doi.org/10.1128/jb.179.6.1846-1851.1997 |
| **Specific mechanistic effect on gp12:** gp57A promotes native short-tail-fiber trimer formation and can reverse aggregation. | Authors proposed gp57A interacts with nascent gp12 to facilitate native trimer formation; at lower temperature gp12 forms higher-order aggregates, and gp57A promotes dissociation back to trimers. (pqac-00000000, pqac-00000006, pqac-00000013) | gp12 is trimeric at **37°C** but forms larger aggregates at **20°C** in the reported assay context. (pqac-00000013) | Matsui et al., 1997, J Bacteriol, https://doi.org/10.1128/jb.179.6.1846-1851.1997 |
| **Cellular localization of function:** gp57A functions **inside the infected bacterial cytoplasm** during phage morphogenesis, not on the mature virion surface. | Its classification as a nonstructural helper/chaperone, absence from mature virions, and role in folding soluble tail-fiber precursors indicate intracellular action during assembly. (pqac-00000002, pqac-00000003, pqac-00000005) | No direct subcellular imaging/localization number reported in retrieved evidence. | Hashemolhosseini et al., 1996, J Bacteriol, https://doi.org/10.1128/jb.178.21.6258-6265.1996; Matsui et al., 1997, J Bacteriol, https://doi.org/10.1128/jb.179.6.1846-1851.1997; Leiman et al., 2010, Virol J, https://doi.org/10.1186/1743-422x-7-355 |
| **Recombinant implementation:** gp57 is practically required for soluble recombinant production of T4 gp37 together with gp38. | A two-vector co-expression system showed single-chaperone expression was insufficient; co-expression of **gp57 + gp38** enabled purification of correctly folded trimeric gp37 for downstream receptor-binding and structural studies. (pqac-00000022, pqac-00000004) | Yield about **4 mg/L** culture; purified gp37 fibers ~**63 nm** by EM; gp57 reported there as **79 aa, 8,613 Da**. (pqac-00000022) | Bartual et al., 2010, Protein Expr Purif, https://doi.org/10.1016/j.pep.2009.11.005; Bartual et al., 2010, PNAS, https://doi.org/10.1073/pnas.1011218107 |
| **Application to host-range engineering:** tail-fiber/chaperone biology informs engineering of adsorption specificity and host range. | T2/T4-like systems use distal tail-fiber genes plus associated helpers/chaperones; swapping tail-fiber determinants can broaden host range, and modern work in other phages shows tail-fiber swaps may require co-swapping an adjacent chaperone gene to alter specificity successfully. (pqac-00000018, pqac-00000020, pqac-00000024) | Engineered/recombined phage examples: IP008 infected **33%** of environmental *E. coli* isolates vs **7%** for T2; one engineered derivative showed **67%** bacteriolytic spectrum among UPEC. (pqac-00000018) | Mahichi et al., 2009, FEMS Microbiol Lett, https://doi.org/10.1111/j.1574-6968.2009.01588.x; Steczynska et al., 2023, bioRxiv, https://doi.org/10.1101/2023.10.16.562632 |
| **Application context in T4 platform engineering:** while gp57 itself is not the display scaffold, understanding T4 tail-fiber assembly supports manipulation of host recognition alongside broader T4 engineering uses such as phage display. | T4 platform reviews note tail fibers mediate host recognition and require gp57 for correct assembly, while separate capsid proteins Hoc/Soc are used for antigen display; thus gp57 is enabling infrastructure for tail-fiber biology rather than the display moiety itself. (pqac-00000019, pqac-00000025) | T4 capsid carries about **160 Hoc** and **960 Soc** copies; example displayed inserts included **36 aa** and **53 aa** chimeric polypeptides. (pqac-00000019, pqac-00000025) | Gamkrelidze & Dąbrowska, 2014, Arch Microbiol, https://doi.org/10.1007/s00203-014-0989-8 |
| **Evidence figure/table support:** review synthesis places gp57A among tail/fiber chaperones and explicitly maps its substrates. | Retrieved Table 2 / Figure 15 summarize gp57A as a chaperone for gp12, gp34, gp37 and show long-tail-fiber assembly context. (pqac-00000015, pqac-00000016, pqac-00000017) | Table entry lists gp57A at **5.7 kDa** with oligomeric mixture annotation. (pqac-00000015, pqac-00000016, pqac-00000017) | Leiman et al., 2010, Virol J, https://doi.org/10.1186/1743-422x-7-355 |


*Table: This table summarizes experimentally grounded functional annotation for Enterobacteria phage T4 gene product 57 (gp57/gp57A), including its chaperone role, assembly targets, biochemical properties, and applied relevance. It is useful as a compact evidence map linking claims to quantitative details and primary sources.*