Stavenuiter and colleagues produced recombinant FSAP (recFSAP) and analysed its suitability for functional studies.

In the recFSAP, the natural activation site (R313-I314) was replaced by a cleavage site for the bacterial protease thermolysin, which prevented the problem of autoactivation and autodegradation observed in natural FSAP. This allowed to otain purified intact FSAP.

Thermolysin activated recFSAP displayed the same affinity for chromogenic peptide substrates as pdFSAP and retained its capability to activate pro-uPA. recFSAP interacted with negatively charged surfaces but did not have FVII-cleaving activity, even in the presence of calcium-ions and lipid vesicles of varying composition. Only On membranes of 100% cardiolipin FVII cleavage did occur, but this resulted in transient activation and rapid degradation.

While recFSAP indeed activates pro-uPA, it does not activate FVII. Whether or not the effect of cardiolipin, which is an intracellular lipid, has any physiological significance remains to be explored.

Title:
Factor VII-activating protease (FSAP): Does it activate Factor VII?

Authors and Source:
F Stavenuiter, E Sellink, HJM Brinkman, AB Meijer, K Mertens
Poster presentation ISTH 2009: OC-WE-084