The interaction between fibrinogen and zymogen FXIII-A2B2 is mediated by fibrinogen residues γ390-396 and the FXIII-B subunits.

Coagulation transglutaminase factor XIII (FXIII) exists in circulation as heterotetrameric proenzyme FXIII-A₂B₂ Effectively all FXIII-A₂B₂ circulates bound to fibrinogen, and excess FXIII-B₂ circulates in plasma. The motifs that mediate interaction of FXIII-A₂B₂ with fibrinogen have been elusive. We recently detected reduced binding of FXIII-A₂B₂ to murine fibrinogen that has γ-chain residues 390-396 mutated to alanines (Fibγ^390-396A). Here, we evaluated binding features using human components, including recombinant fibrinogen variants, FXIII-A₂B₂, and isolated FXIII-A₂ and -B₂ homodimers. FXIII-A₂B₂ coprecipitated with wild-type (γA/γA), alternatively-spliced (γ'/γ'), and αC-truncated (Aα251) fibrinogens, whereas coprecipitation with human Fibγ^390-396A was reduced by 75% (P <0001). Surface plasmon resonance showed γA/γA, γ'/γ', and Aα251 fibrinogens bound FXIII-A₂B₂ with high affinity (nanomolar); however, Fibγ^390-396A did not bind FXIII-A₂B₂ These data indicate fibrinogen residues γ390-396 comprise the major binding motif for FXIII-A₂B₂ Compared with γA/γA clots, FXIII-A₂B₂ activation peptide release was 2.7-fold slower in Fibγ^390-396A clots (P < .02). Conversely, activation of recombinant FXIII-A₂ (lacking FXIII-B₂) was similar in γA/γA and Fibγ^390-396A clots, suggesting fibrinogen residues γ390-396 accelerate FXIII-A₂B₂ activation in a FXIII-B₂-dependent mechanism. Recombinant FXIII-B₂ bound γA/γA, γ'/γ', and Aα251 with similar affinities as FXIII-A₂B₂, but did not bind or coprecipitate with Fibγ^390-396A FXIII-B₂ also coprecipitated with fibrinogen from FXIII-A-deficient mouse and human plasmas. Collectively, these data indicate that FXIII-A₂B₂ binds fibrinogen residues γ390-396 via the B subunits, and that excess plasma FXIII-B₂ is not free, but rather circulates bound to fibrinogen. These findings provide insight into assembly of the fibrinogen/FXIII-A₂B₂ complex in both physiologic and therapeutic situations.

KEYWORDS: {{ getKeywords(articleDetailText.words) }}