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

Abstract

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

Freeze‐dried plasma enhances clot formation and inhibits fibrinolysis in the presence of tissue plasminogen activator similar to pooled liquid plasma

“…Factor XIIIA levels were similar in the plasma groups. High free Factor XIIIB levels in pFDP, although recently shown to bind fibrinogen, did not impact the TEG angle. Increased levels of Factor XI and protein C in FDP did not impact the rate of clot initiation (R‐time) or formation (angle) in the TEG tracings, and their functions are known to oppose each other.…”

The factor XIII‐A Val34Leu polymorphism decreases whole blood clot mass at high fibrinogen concentrations

“…Factor XIII (FXIII) is a protransglutaminase present in cells and plasma. Plasma FXIII is a noncovalent heterotetramer (FXIII‐A 2 B 2 ) that circulates bound to fibrinogen . During coagulation, FXIII is activated by thrombin‐mediated cleavage and release of 37‐amino acid (4‐kDa) activation peptides from the N‐termini of the catalytic FXIII‐A 2 subunits, followed by calcium‐mediated dissociation of the carrier FXIII‐B 2 subunits .…”

“…Plasma FXIII is a noncovalent heterotetramer (FXIII-A 2 B 2 ) that circulates bound to fibrinogen. 1 During coagulation, FXIII is activated by thrombin-mediated cleavage and release of 37-amino acid (4-kDa) activation peptides from the N-termini of the catalytic FXIII-A 2 subunits, followed by calcium-mediated dissociation of the carrier FXIII-B 2 subunits. 2 Activated FXIII catalyzes the formation of ε-N-(γ-glutamyl)-lysyl crosslinks between γ-and α-chains of fibrin 3 and between fibrin and other plasma proteins.…”

Fibrinogen and factor XIII: newly recognized roles in venous thrombus formation and composition

“…(40) FXIII-A 2 B 2 circulates in plasma bound to fibrinogen at residues γ-chain 390–396 and possibly also to α-chain residue E396. (30, 41, 42) During coagulation, thrombin rapidly cleaves N-terminal peptides from the FXIII A-subunits. Calcium then induces a conformational change in FXIII, which promotes release of the FXIII-B subunits and yields fully activated FXIII-A 2 * (FXIIIa).…”

“…(31) Since plasma FXIII circulates bound to fibrin, it is rapidly converted to FXIIIa in concert with fibrin formation and can fulfill this temporal requirement for fibrin crosslinking. (41) In contrast, slower exposure of platelet FXIII likely happens after clot contraction – too late to mechanically stabilize fibrin fibers and enable them to retain RBCs during clot contraction.…”