| Functional aspect | Key findings | Evidence type | Primary supporting citations with year/URL |
|---|---|---|---|
| Adsorption role | • gp12 is the T4 short tail fiber (STF) that mediates the irreversible or pseudo-irreversible adsorption step after long-tail-fiber sampling • STF engagement anchors the baseplate for downstream sheath contraction and DNA delivery (pqac-00000002, pqac-00000019, pqac-00000021) | Review/mechanistic model; comparative structural review | Mourosi et al., 2022, https://doi.org/10.3390/ijms232012146; Klein-Sousa et al., 2024, https://doi.org/10.1101/2024.10.28.620165 |
| Receptor specificity | • gp12 binds the core region of E. coli LPS • authoritative reviews/primary studies variously localize this to the lipid A–inner core region, the inner core/heptose region, or broadly the LPS core/outer-core interface, indicating consensus on core-LPS targeting but some wording differences across sources (pqac-00000004, pqac-00000005, pqac-00000002, pqac-00000021) | X-ray structure paper context; genome/review synthesis; mechanistic review | Thomassen et al., 2003, https://doi.org/10.1016/S0022-2836(03)00755-1; van Raaij et al., 2001, https://doi.org/10.1006/jmbi.2000.5204; Mourosi et al., 2022, https://doi.org/10.3390/ijms232012146 |
| Structural organization | • gp12 is a parallel, in-register homotrimer • each monomer is 527 aa (~55.3 kDa) • there are 18 gp12 subunits per virion tail (6 STF trimers) (pqac-00000003, pqac-00000004, pqac-00000007, pqac-00000010) | X-ray structure; tail morphogenesis review | Hyman & van Raaij, 2018, https://doi.org/10.1007/s12551-017-0348-5; Thomassen et al., 2003, https://doi.org/10.1016/S0022-2836(03)00755-1; Leiman et al., 2010, https://doi.org/10.1186/1743-422X-7-355 |
| Domain architecture and receptor-binding fold | • C-terminal receptor-binding domain includes head and bonnet subdomains • central right-handed triple-stranded β-helix plus a knitted globular C-terminal domain • trimer buries ~7400 Ų total (~60% of monomer surface) (pqac-00000004, pqac-00000006, pqac-00000009) | X-ray crystallography | Thomassen et al., 2003, https://doi.org/10.1016/S0022-2836(03)00755-1; van Raaij et al., 2001, https://doi.org/10.1006/jmbi.2000.5204 |
| Metal binding | • gp12 contains a Zn-binding site in the C-terminal domain • Zn2+ is coordinated octahedrally by His445 and His447 from each of the three protomers • this unusual metallocenter likely stabilizes the trimeric receptor-binding tip (pqac-00000004, pqac-00000006, pqac-00000009) | X-ray crystallography; structural interpretation | Thomassen et al., 2003, https://doi.org/10.1016/S0022-2836(03)00755-1; Leiman et al., 2010, https://doi.org/10.1186/1743-422X-7-355 |
| Structural resources | • experimentally determined gp12 fragments are represented by PDB entries 1H6W and 1OCY • the 2003 structure paper explicitly links 1H6W to a 33-kDa C-terminal fragment (pqac-00000004, pqac-00000007) | X-ray structure; database-linked structural review | Thomassen et al., 2003, https://doi.org/10.1016/S0022-2836(03)00755-1; Leiman et al., 2010, https://doi.org/10.1186/1743-422X-7-355 |
| Assembly/localization in the virion | • gp12 N-termini attach to gp10 trimers in the T4 baseplate • gp11 trimers hold gp12 at a hinge about halfway along the fiber • gp12 localizes to the outer rim of the baseplate and is added late in tail assembly (pqac-00000003, pqac-00000004, pqac-00000007, pqac-00000010) | Structural review; morphogenesis review; primary crystallography context | Hyman & van Raaij, 2018, https://doi.org/10.1007/s12551-017-0348-5; Leiman et al., 2010, https://doi.org/10.1186/1743-422X-7-355; Thomassen et al., 2003, https://doi.org/10.1016/S0022-2836(03)00755-1 |
| Chaperone requirement | • proper folding/trimerization of gp12 requires the phage chaperone gp57/gp57A • full-length gp12 aggregates readily without correct assisted folding • recombinant expression with gp57 yields native-like trimers (pqac-00000004, pqac-00000009, pqac-00000011, pqac-00000012) | X-ray structure context; biochemical expression study | Thomassen et al., 2003, https://doi.org/10.1016/S0022-2836(03)00755-1; Leiman et al., 2010, https://doi.org/10.1186/1743-422X-7-355; Miernikiewicz et al., 2016, https://doi.org/10.3389/fmicb.2016.01112 |
| Triggering mechanism during infection | • after reversible long-tail-fiber contact, a mechanical signal converts the baseplate conformation • STFs are unpinned, rotate downward, and bind LPS • this reorients the baseplate parallel to the cell surface and promotes sheath contraction/genome injection (pqac-00000002, pqac-00000021) | Mechanistic review/model | Mourosi et al., 2022, https://doi.org/10.3390/ijms232012146 |
| LPS-binding structural model | • the trimer apex is positively charged with grooves lined by aromatic/basic residues • each groove was proposed to bind one LPS molecule, with phosphates engaging basic residues and sugars contacting aromatic residues • multivalency explains quasi-irreversible adsorption (pqac-00000006) | X-ray structure-based binding model | Thomassen et al., 2003, https://doi.org/10.1016/S0022-2836(03)00755-1 |
| Quantitative experimental data: oligomerization and LPS complex formation | • recombinant gp12 runs as ~172.5 kDa trimer and ~57.5 kDa monomer by SDS-PAGE • DLS showed gp12 alone ~51 nm and LPS alone ~95.45 nm • mixed gp12+LPS formed complexes averaging ~1980 nm within minutes and stabilizing near ~2000 nm after ~45 min (pqac-00000011, pqac-00000012, pqac-00000014) | Biochemical assay (SDS-PAGE, DLS) | Miernikiewicz et al., 2016, https://doi.org/10.3389/fmicb.2016.01112 |
| Quantitative in vivo data relevant to function/application | • in LPS-challenged mice, gp12 reduced serum IL-1α by 72% at 7 h (p=0.002) • IL-6 was reduced by 48% at 3 h (p=0.001) • histopathology showed reduced inflammatory infiltrates in liver and spleen, with broader attenuation in spleen/liver/kidney/lung (pqac-00000011) | In vivo murine study | Miernikiewicz et al., 2016, https://doi.org/10.3389/fmicb.2016.01112 |
| Biological pathway context | • gp12 functions in the adsorption/penetration phase of the T4 infection cycle rather than as an enzyme • it acts as the secondary receptor-binding element connecting host recognition to conformational activation of the contractile tail machine (pqac-00000002, pqac-00000021) | Mechanistic review | Mourosi et al., 2022, https://doi.org/10.3390/ijms232012146 |
| Applications and engineering relevance | • recombinant gp12 can bind purified LPS and modulate LPS-induced inflammation, suggesting use as an LPS-sequestering biologic • tail fibers are major host-range determinants and attractive engineering targets for diagnostics, biocontrol, and phage therapy • gp12-like STF modules inform RBP swapping/chimera design (pqac-00000011, pqac-00000019, pqac-00000022) | Biochemical/in vivo; computational/engineering; translational review | Miernikiewicz et al., 2016, https://doi.org/10.3389/fmicb.2016.01112; Klein-Sousa et al., 2024, https://doi.org/10.1101/2024.10.28.620165; Oliveira et al., 2023, https://doi.org/10.1007/s00253-023-12547-8 |
| Recent 2023-2024 developments | • 2024 RBPseg/structure-atlas work explicitly cites T4 gp12 as the STF responsible for pseudo-irreversible LPS binding • recent RBP studies emphasize modularity, domain exchange, and structure-guided engineering of tail fibers • 2023 T-even-like phage studies continue to use the T4 STF/LTF paradigm for interpreting host-range mechanisms (pqac-00000019, pqac-00000022) | Computational/engineering; contemporary comparative phage biology | Klein-Sousa et al., 2024, https://doi.org/10.1101/2024.10.28.620165; Oliveira et al., 2023, https://doi.org/10.1007/s00253-023-12547-8 |


*Table: This table summarizes the experimentally supported function, structure, assembly, and application relevance of Enterobacteria phage T4 gene product 12 (gp12), with emphasis on adsorption to LPS and recent 2023-2024 context. It is useful as a compact evidence map for functional annotation and literature-supported reporting.*