| Topic | Key claim/data | Evidence type | Source (first author, year, journal) | Publication date/month | URL/DOI |
|---|---|---|---|---|---|
| Identity | In bacteriophage T4, late gene **wac** encodes **fibritin** (also called **gpwac/Wac**); the name is linked to **“whisker antigen control”** and the protein builds the collar/whiskers complex on the phage neck. (pqac-00000008, pqac-00000009, pqac-00000015) | Genetic, structural, review | Letarov 2005, *Journal of Bacteriology*; Efimov 2005, *Virus Genes*; Hu 2015, *PNAS* | Feb 2005; Jun 2005; Aug 2015 | https://doi.org/10.1128/jb.187.3.1055-1066.2005 ; https://doi.org/10.1007/bf01702598 ; https://doi.org/10.1073/pnas.1501064112 |
| Localization | Fibritin/Wac localizes to the **virion neck**, forming the **collar and whiskers** just below the head-tail junction. (pqac-00000008, pqac-00000013, pqac-00000015) | Cryo-EM, structural analysis | Letarov 2005, *Journal of Bacteriology*; Fokine 2013, *Journal of Molecular Biology*; Hu 2015, *PNAS* | Feb 2005; May 2013; Aug 2015 | https://doi.org/10.1128/jb.187.3.1055-1066.2005 ; https://doi.org/10.1016/j.jmb.2013.02.012 ; https://doi.org/10.1073/pnas.1501064112 |
| Copy number | Cryo-EM and structural interpretation indicate **12 Wac/fibritin molecules per virion**, arranged as **6 forming the collar** and **6 forming the whiskers**. (pqac-00000004, pqac-00000013, pqac-00000015) | Cryo-EM, structural modeling | Fokine 2013, *Journal of Molecular Biology*; Hu 2015, *PNAS* | May 2013; Aug 2015 | https://doi.org/10.1016/j.jmb.2013.02.012 ; https://doi.org/10.1073/pnas.1501064112 |
| Oligomeric state | Individual fibritin molecules are **trimers**; the protein is a trimeric elongated fiber and can be SDS-resistant in oligomeric form. (pqac-00000001, pqac-00000005, pqac-00000007) | Biochemical, structural | Leiman 2010, *Virology Journal*; Letarov 2005, *Journal of Bacteriology* | Dec 2010; Feb 2005 | https://doi.org/10.1186/1743-422x-7-355 ; https://doi.org/10.1128/jb.187.3.1055-1066.2005 |
| Structure/domains | T4 fibritin is a **~486–487 aa** segmented fibrous protein with a conserved **N-terminal neck-binding domain (~50 aa / residues 1–80 modeled)**, a long **central coiled-coil shaft**, and a **C-terminal foldon (~30 aa)** that initiates trimerization and correct folding. (pqac-00000000, pqac-00000002, pqac-00000003, pqac-00000005, pqac-00000009) | X-ray/cryo-EM modeling, biochemical | Letarov 2005, *Journal of Bacteriology*; Fokine 2013, *Journal of Molecular Biology*; Efimov 2005, *Virus Genes* | Feb 2005; May 2013; Jun 2005 | https://doi.org/10.1128/jb.187.3.1055-1066.2005 ; https://doi.org/10.1016/j.jmb.2013.02.012 ; https://doi.org/10.1007/bf01702598 |
| Quantitative dimensions | Reported dimensions include fibritin length of **~480 Å** or **~530 Å / 53 nm**, diameter **~20 Å**, and a neck collar of **~300 Å diameter** and **~40 Å thickness**. (pqac-00000000, pqac-00000001, pqac-00000016) | Cryo-EM, structural review, super-resolution implementation | Letarov 2005, *Journal of Bacteriology*; Leiman 2010, *Virology Journal*; Gallea 2024, *bioRxiv* | Feb 2005; Dec 2010; Apr 2024 | https://doi.org/10.1128/jb.187.3.1055-1066.2005 ; https://doi.org/10.1186/1743-422x-7-355 ; https://doi.org/10.1101/2024.04.04.588072 |
| Assembly role | During morphogenesis, fibritin/Wac acts as a **chaperone/scaffold for long tail fiber (LTF) attachment**, helping position assembled LTFs for joining to the baseplate; without fibritin, LTF attachment is very slow. (pqac-00000000, pqac-00000001, pqac-00000013) | Genetic, structural, morphogenesis studies | Letarov 2005, *Journal of Bacteriology*; Leiman 2010, *Virology Journal*; Fokine 2013, *Journal of Molecular Biology* | Feb 2005; Dec 2010; May 2013 | https://doi.org/10.1128/jb.187.3.1055-1066.2005 ; https://doi.org/10.1186/1743-422x-7-355 ; https://doi.org/10.1016/j.jmb.2013.02.012 |
| Infectivity role | Post-lysis, Wac/fibritin acts as an **environmental sensor** that helps keep long tail fibers **retracted under unfavorable conditions**, thereby modulating adsorption and infectivity. (pqac-00000000, pqac-00000004, pqac-00000008) | Genetic, functional interpretation | Letarov 2005, *Journal of Bacteriology*; Fokine 2013, *Journal of Molecular Biology* | Feb 2005; May 2013 | https://doi.org/10.1128/jb.187.3.1055-1066.2005 ; https://doi.org/10.1016/j.jmb.2013.02.012 |
| Mutant phenotype | **wac is nonessential** for T4 viability, but **wac mutants form small plaques** and display defective/short-stub long tail fiber presentation in structural analyses. (pqac-00000015) | Genetic, cryo-EM | Hu 2015, *PNAS* | Aug 2015 | https://doi.org/10.1073/pnas.1501064112 |
| Cryo-EM / structural resources | Fokine et al. fitted fibritin models built from **N-terminal residues 1–80** and **C-terminal residues 371–483** plus modeled coiled-coil into T4 neck density; reported resources include **PDB 3J2O** and **EMD-5528**, with final cryo-EM reconstruction at **~25 Å**. (pqac-00000002) | Cryo-EM, model fitting | Fokine 2013, *Journal of Molecular Biology* | May 2013 | https://doi.org/10.1016/j.jmb.2013.02.012 |
| Application: T4 display | The outward-exposed C terminus of fibritin can be **lengthened/fused to foreign peptides** without abolishing folding or neck binding; engineered T4 particles displayed a **53-residue insert** including **45 aa from HBV pre-S2**. (pqac-00000025, pqac-00000026) | Engineering, phage display | Efimov 2005, *Virus Genes*; Gamkrelidze 2014, *Archives of Microbiology* | Jun 2005; May 2014 | https://doi.org/10.1007/bf01702598 ; https://doi.org/10.1007/s00203-014-0989-8 |
| Application: super-resolution bionanoruler | A 2024 preprint used **anti-fibritin/Wac labeling** in **Exchange 3D DNA-PAINT** to image T4 as a **3D bio-nanoruler**, resolving the expected fibrous collar morphology and reporting **six 53 nm whiskers**; instrumentation metrics included **~3 nm FRC effective resolution** and **~7 nm linkage error**. (pqac-00000016, pqac-00000017, pqac-00000018) | Super-resolution imaging, engineering | Gallea 2024, *bioRxiv* | Apr 2024 | https://doi.org/10.1101/2024.04.04.588072 |
| Application: adenovirus targeting | T4 fibritin was used to engineer **adenovirus vectors** by replacing the native fiber with a **fiber-fibritin chimera**, enabling **receptor-specific gene delivery**. (pqac-00000024) | Viral engineering, gene delivery | Krasnykh 2001, *Journal of Virology* | May 2001 | https://doi.org/10.1128/jvi.75.9.4176-4183.2001 |
| Application: foldon as trimerization tag | The fibritin **foldon** is an autonomously folding trimerization domain that has been widely repurposed as a **trimerization/registration tag** for chimeric fibrous proteins, producing **highly stable SDS-resistant trimers** and aiding structural biology and nanostructure engineering. (pqac-00000020, pqac-00000021, pqac-00000022, pqac-00000023) | Protein engineering, structural biology | Papanikolopoulou 2004, *J Mol Biol*; Papanikolopoulou 2004, *JBC*; Papanikolopoulou 2008, *Methods Mol Biol*; Boudko 2002, *Eur J Biochem* | Sep 2004; Mar 2004; Jan 2008; Feb 2002 | https://doi.org/10.1016/j.jmb.2004.07.008 ; https://doi.org/10.1074/jbc.m311791200 ; https://doi.org/10.1007/978-1-59745-480-3_2 ; https://doi.org/10.1046/j.1432-1033.2002.02734.x |


*Table: This table summarizes the core functional annotation, structural biology, and applied engineering evidence for bacteriophage T4 gene wac/fibritin. It highlights identity verification, virion localization, quantitative structural parameters, and validated applications supported by the gathered sources.*