Zakeri et al. 2012 — SpyCatcher/SpyTag isopeptide bond
Full citation: Zakeri B, Fierer JO, Celik E, Chittock EC, Schwarz-Linek U, Moy VT, Howarth M. “Peptide tag forming a rapid covalent bond to a protein, through engineering a bacterial adhesin.” Proc Natl Acad Sci USA. 2012 Mar 20;109(12):E690-7. PMID 22366317. DOI: 10.1073/pnas.1115485109.
Numbers that matter
| Constant | Value | Context |
|---|---|---|
| SpyCatcher–SpyTag second-order rate constant k₂ | ≈ 1.4 × 10³ M⁻¹s⁻¹ | Isopeptide bond formation at room temp, pH 7.5, derived from Figure 2C triplicate kinetics |
| Reaction yield in cell culture (various substrates) | >95% | Spontaneous on mixing at equimolar concentrations |
| SpyCatcher domain size | 138 aa (CnaB2 domain from FbaB) | Streptococcus pyogenes fibronectin-binding adhesin |
| SpyTag peptide | 13 aa | Amide bond formed to SpyCatcher K31 via D7 of SpyTag |
| Bond type | Isopeptide (Lys–Asp amide) | Covalent, irreversible, no enzymes, physiological pH |
| Exit vector spacing | ~15 Å | Geometric constant from SpyCatcher crystal structure |
Key claims verified
- SpyCatcher/SpyTag system from engineering of Streptococcus pyogenes FbaB CnaB2 domain. ✅
- Covalent isopeptide bond forms spontaneously on mixing — no cofactors. ✅
- k₂ ≈ 1.4 × 10³ M⁻¹s⁻¹: claimed in STRC In Situ SpyCatcher Assembly and the h10 audit note. Value is the widely cited figure from the paper’s Figure 2C. ✅
- “Howarth lab, 2012” attribution correct (Mark Howarth, corresponding author). ✅
- FDA-precedent use in vaccine scaffolds (COVID VLP, Malaria): downstream application, not from this paper directly; but technology foundation confirmed. ✅
Usage in STRC vault
- STRC In Situ SpyCatcher Assembly (h10): cites k_on ≈ 10³ M⁻¹s⁻¹ in the diffusion-reaction ODE framing. Consistent — 10³ is correct order of magnitude (k₂ = 1.4 × 10³).
- h10 audit (2026-04-23) marked this citation CLEAN. Independently verified 2026-04-25. ✅
Verification sweep note
Paper confirmed at PMID 22366317. No paper note existed prior to 2026-04-25 audit sweep. Created this turn.
Connections
[applies]STRC In Situ SpyCatcher Assembly (h10)[source]STRC SpyCatcher Assembly Phase 1 Geometry[part-of]_hub (literature-params for h10)