Losac, the first hemolin that exhibits procogulant activity through selective factor X proteolytic activation

Area of Science:

• Biochemistry
• Toxicology
• Molecular Biology

Background:

• Lonomia obliqua caterpillar envenoming causes hemorrhagic syndrome and consumptive coagulopathy.
• Losac, a component of L. obliqua bristles, activates factor X and is implicated in the syndrome.
• Losac exhibits proteolytic activity and homology to hemolin family proteins, not known proteases.

Purpose of the Study:

• To characterize the proteolytic activity of Losac.
• To demonstrate the feasibility of recombinant Losac (rLosac) production.
• To validate Losac as a procoagulant factor responsible for envenoming.

Main Methods:

• Recombinant production of Losac (rLosac).
• Assays to measure coagulation time in normal and deficient plasmas.
• Factor X activation assays with varying concentrations of rLosac, phospholipids, and calcium ions.
• Kinetic analysis (Michaelis-Menten) and fragment analysis of cleaved factor X.

Main Results:

• rLosac shortened coagulation time in normal and factor X-deficient plasmas (when reconstituted).
• rLosac activated factor X in a dose- and time-dependent manner, requiring phospholipids and calcium.
• rLosac exhibited Michaelis-Menten kinetics and produced factor X fragments similar to RVV-X.

Conclusions:

• Losac is the first identified hemolin family protein with procoagulant activity.
• Losac selectively cleaves coagulation factor X, contributing to the hemorrhagic syndrome of Lonomia obliqua envenoming.
• Recombinant production of Losac is feasible, offering potential for further research and antivenom development.