The interaction between fibrinogen and zymogen FXIII-A2B2 is mediated by fibrinogen residues ?390-396 and the FXIII-B subunits.

ABSTRACT: 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 ?-chain residues 390-396 mutated to alanines (Fib?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 (?A/?A), alternatively-spliced (?'/?'), and ?C-truncated (A?251) fibrinogens, whereas coprecipitation with human Fib?390-396A was reduced by 75% (P <0001). Surface plasmon resonance showed ?A/?A, ?'/?', and A?251 fibrinogens bound FXIII-A2B2 with high affinity (nanomolar); however, Fib?390-396A did not bind FXIII-A2B2 These data indicate fibrinogen residues ?390-396 comprise the major binding motif for FXIII-A2B2 Compared with ?A/?A clots, FXIII-A2B2 activation peptide release was 2.7-fold slower in Fib?390-396A clots (P < .02). Conversely, activation of recombinant FXIII-A2 (lacking FXIII-B2) was similar in ?A/?A and Fib?390-396A clots, suggesting fibrinogen residues ?390-396 accelerate FXIII-A2B2 activation in a FXIII-B2-dependent mechanism. Recombinant FXIII-B2 bound ?A/?A, ?'/?', and A?251 with similar affinities as FXIII-A2B2, but did not bind or coprecipitate with Fib?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 ?390-396 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.

SUBMITTER: Byrnes JR 

PROVIDER: S-EPMC5064719 | biostudies-literature | 2016 Oct

REPOSITORIES: biostudies-literature