| Claim/Parameter | Value | Experimental context/method | Source (with year) |
|---|---|---|---|
| Verified identity | Soc = small outer capsid protein of Enterobacteria phage T4; nonessential outer capsid decoration/stabilization protein, ~9–10 kDa | Structural/biochemical literature on T4 capsid proteins; distinct from unrelated non-phage “soc” genes | Iwasaki et al., 2000; Rao & Black, 2010; Fokine et al., 2023 (pqac-00000007, pqac-00000006, pqac-00000024) |
| Primary function | Capsid clamp/glue that reinforces the mature T4 head by bridging adjacent gp23* hexons/capsomers | Cryo-EM, structural interpretation, biochemical review | Iwasaki et al., 2000; Rao & Black, 2010; Fokine et al., 2023 (pqac-00000007, pqac-00000025, pqac-00000024) |
| Cellular/virion localization | Exterior of mature capsid head shell; binds after capsid maturation/expansion rather than during initial shell assembly | Cryo-EM and assembly studies on mature/expanded heads | Iwasaki et al., 2000; Rao & Black, 2010; Fokine et al., 2023 (pqac-00000007, pqac-00000025, pqac-00000031) |
| Binding location on capsid | Interfaces between adjacent gp23* hexameric capsomers; absent at gp24* pentamer/vertex interfaces and hexamer–portal interfaces | Cryo-EM mapping and structural analysis | Iwasaki et al., 2000; Li et al., 2007; Fokine et al., 2023 (pqac-00000007, pqac-00000026, pqac-00000024) |
| Binding geometry | Soc forms trimers at local/quasi-3-fold axes and dimers/monomers at local/quasi-2-fold or vertex-proximal sites; each Soc contacts two neighboring capsomers | Cryo-EM, capsid lattice interpretation, assembly schematics | Iwasaki et al., 2000; Li et al., 2007 (pqac-00000007, pqac-00000028, pqac-00000015) |
| Capsid-binding region vs exposed regions | Central region mediates capsid binding; both N- and C-termini are surface/solvent exposed | Fusion-protein assembly studies; structural interpretation | Li et al., 2007; Zhu et al., 2024 (pqac-00000001, pqac-00000018) |
| Soc copy number per capsid (classic estimate) | ~810 copies/capsid | Quantitative capsid decoration estimates from T4 display studies | Li et al., 2006; Li et al., 2007 (pqac-00000002, pqac-00000029) |
| Soc binding sites per capsid (later estimate) | Up to 870 sites/capsid when fully occupied | Structural review/synthesis of T4 head architecture | Rao & Black, 2010; Fokine et al., 2023; Zhu et al., 2024 (pqac-00000025, pqac-00000031, pqac-00000018) |
| Clamp/cage stoichiometry | ~270 trimeric Soc clamps can form a reinforcing outer cage on the capsid | Review of structural data | Rao & Black, 2010 (pqac-00000025) |
| Affinity of recombinant Soc for capsid | Apparent Kd ~73 nM at 8 °C; ~54 nM at room temperature | In vitro saturation binding/Scatchard analyses on hoc−soc− capsids | Li et al., 2007 (pqac-00000001, pqac-00000027, pqac-00000016) |
| Saturation concentration | Binding saturated at ~4.6 μM Soc in the reported assay | In vitro binding curves | Li et al., 2007 (pqac-00000001) |
| Bmax for recombinant Soc | ~746 copies/capsid | Densitometry-based saturation binding on purified capsids | Li et al., 2007 (pqac-00000027) |
| Bmax for double-fusion LFn–Soc–PA4 | ~769 copies/capsid; effective dual-terminal display interpreted as 1,538 displayed moieties | In vitro binding with dual-terminal antigen fusion | Li et al., 2007 (pqac-00000027) |
| Effect of large fusions on affinity/capacity | Bulky PA/LF fusions weakened binding ~10-fold (Kd ~745–784 nM) and lowered Bmax to ~352–365 copies/capsid | In vitro binding of full-length anthrax toxin fusions to capsids | Li et al., 2007 (pqac-00000026, pqac-00000027) |
| Oligomeric state in solution | Soc behaves as a monomer in solution; oligomerization/clamping is imposed by capsid template | Analytical ultracentrifugation / gel filtration and structural interpretation | Iwasaki et al., 2000; Li et al., 2007 (pqac-00000007, pqac-00000003) |
| Alkaline pH stability phenotype | Soc-minus phage lose viability at pH 10.6; wild-type or Soc-supplemented particles remain much more stable | Infectivity assays after alkaline treatment | Rao & Black, 2010; Li et al., 2007 (pqac-00000025, pqac-00000029, pqac-00000030) |
| Quantified alkaline protection | Addition of Soc enhances survival by ~10^4-fold under extreme alkaline conditions; wild-type/rSoc-supplemented phage retained ~75–85% titer after pH 10.4 treatment whereas hoc−soc− phage lost >98% | Review synthesis plus primary infectivity experiments | Rao & Black, 2010; Li et al., 2007 (pqac-00000025, pqac-00000030) |
| Stability of bound Soc-fusion proteins | No dissociation of Soc–anthrax fusions after exposure to pH 10.4 | Capsid-bound fusion stability test | Li et al., 2007 (pqac-00000028, pqac-00000030) |
| Relative contribution of Soc–Soc interfaces | When inter-Soc interactions were perturbed, only ~8% survival remained with trimeric-interface reinforcement and ~4.2% with dimeric-interface reinforcement at pH 10.6 | Engineered fusion constructs probing inter-Soc contacts | Li et al., 2007 (pqac-00000005, pqac-00000028) |
| Thermal stability effect | Soc raises T4 capsid thermal denaturation temperature by ~6 °C; Soc-decorated capsids tolerate up to ~60 °C in review summaries | Structural/biophysical analysis and review synthesis | Iwasaki et al., 2000; Rao & Black, 2010 (pqac-00000032, pqac-00000025) |
| Other protective effects | Soc helps stabilize capsids against osmotic shock and denaturants | Review synthesis from T4 head studies | Rao & Black, 2010 (pqac-00000025) |
| Maximum anchored fusion size | Soc can stably anchor proteins up to ~93 kDa in reported experiments | Soc fusion display with anthrax proteins | Li et al., 2007 (pqac-00000026, pqac-00000029) |
| Combined display capacity on T4 surface | Soc + Hoc together can support up to ~1,775 displayed antigens/capsid; experimentally ~1,662 anthrax-related molecules were achieved | In vitro assembly of Hoc and Soc fusion proteins | Li et al., 2007 (pqac-00000001, pqac-00000011) |
| Soc-only high-density display capacity | Up to ~1,620 displayed antigens/capsid in dual-terminal Soc fusion configurations | In vitro display with both Soc termini used | Li et al., 2007 (pqac-00000001) |
| Macromolecular assembly benchmark | Up to 229 anthrax toxin complexes assembled on one capsid, corresponding to ~2,400 protein molecules and ~133 MDa anchored mass | Sequential in vitro assembly via Soc/Hoc fusions | Li et al., 2006 (pqac-00000002, pqac-00000012) |
| 2023 understanding of biological role | Soc and Soc–gp23*/Soc–Soc interactions form an external cage that protects virions from harsh environmental conditions such as pH and temperature extremes, relevant to survival in environments like the gut | 2023 review integrating structural and functional evidence | Fokine et al., 2023 (pqac-00000000, pqac-00000024, pqac-00000031) |
| 2024 platform view | Soc is one of ~870 nonessential exposed capsid proteins used as a modular “plug-and-play” engineering site; both termini are engineerable and antigen spacing/copy number can be tuned | Annual Review synthesis of T4 vaccine platform | Zhu et al., 2024 (pqac-00000008, pqac-00000009, pqac-00000018) |
| 2024 engineering methods | Soc-fused antigens can be displayed by purified-protein in vitro assembly, in vivo expression during phage production, CRISPR engineering, or Soc-SpyCatcher/SpyTag coupling | Review of platform methods and vaccine design strategies | Zhu et al., 2024 (pqac-00000008, pqac-00000020, pqac-00000021) |
| 2024 antigen display examples | Large antigens displayed via Soc include anthrax PA (~83 kDa) and SARS-CoV-2 spike ectodomain (~435 kDa) in review examples | Review summarizing prior primary studies and newer T4-COVID designs | Zhu et al., 2024 (pqac-00000008) |
| 2024 quantitative vaccine examples | T4-(F1mut-V-Soc) displayed ~663 copies/capsid; dual-display plague/anthrax constructs showed ~650 copies of F1mut-V-Soc and ~360 copies of Soc-PA; T4-Soc-PA showed ~355 PA molecules/phage | Vaccine-focused review citing animal studies | Zhu et al., 2024 (pqac-00000017, pqac-00000019) |
| 2024 mucosal/intranasal vaccine outcomes | Soc-based T4 vaccines delivered intranasally induced mucosal sIgA and systemic responses; review cites examples of complete protection in influenza models and 100% protection in plague challenge models in mice and Brown Norway rats | Annual Review synthesis of preclinical animal studies | Zhu et al., 2024 (pqac-00000017, pqac-00000019, pqac-00000020) |


*Table: This table summarizes experimentally supported functional, structural, quantitative, and application-focused facts about bacteriophage T4 Soc (UniProt P03715). It consolidates classic primary literature and 2023-2024 review evidence on binding geometry, stoichiometry, stability, and use as a high-density antigen display scaffold.*