Degradation of human factor XIII by lonomin V, a purified fraction of Lonomia achelous caterpillar venom.

Lonomia achelous caterpillar venom (LACV) causes a severe bleeding diathesis in humans. A constant finding in these cases is a profound depression of blood clotting Factor XIII (FXIII) activity. The molecular mechanisms by which LONOMIN V (a chromatographically purified fraction from LACV) alters the FXIII complex is the subject of the present study. Incubation of human purified FXIII with Lonomin V shows that both the zymogen and the activated forms of FXIII were proteolytically degraded, with the generation of peptidic fragments of low molecular weight. Both the A and B subunits of FXIII were degraded in a progressive, dose dependent manner. The B subunit was more resistant to the action of Lonomin V, requiring higher concentrations in order to achieve complete degradation. On the basis of these findings we postulate that the proteolysis of FXIII in vivo is one of the pathophysiological factors behind this bleeding syndrome.