Summary
The first step of coagulation factor XIII (FXIII) activation involves cleavage of
the FXIII activation peptide (FXIII-AP) by thrombin. However, it is not known whether
the FXIII-AP is released into plasma upon cleavage or remains attached to activated
FXIII. The aim of the present work was to study the structure of free FXIII-AP, develop
an assay for FXIII-AP determination in human plasma, and to answer the question whether
FXIII-AP is released into plasma. We used ab-initio modeling and molecular dynamics
simulations to study the structure of free FXIII-AP. We raised monoclonal and polyclonal
antibodies against FXIII-AP and developed a highly sensitive and specific ELISA method
for direct detection of FXIII-AP in human plasma. Structural analysis showed a putative
different conformation of the free FXIII-AP compared to FXIII-AP bound to the FXIII
protein. We concluded that it might be feasible to develop specific antibodies against
the free FXIII-AP. Using our new FXIII-AP ELISA, we found high levels of FXIII-AP
in in-vitro activated plasma samples and serum. We showed for the first time that
FXIIIAP is detached from activated FXIII and is released into plasma, where it can
be directly measured. Our findings may be of major clinical interest in regard to
a possible new marker in thrombotic disease.
Keywords
factor XIII - activation peptide - activation marker - molecular dynamics simulations