Abstract
Snake venom metalloproteinases (SVMPs) are major components in most viperid venoms that induce disturbances in the hemostatic system and tissues of animals envenomated by snakes. These disturbances are involved in human pathology of snake bites and appear to be essential for the capture and digestion of snake's prey and avoidance of predators. SVMPs are a versatile family of venom toxins acting on different hemostatic targets which are present in venoms in distinct structural forms. However, the reason why a large number of different SVMPs are expressed in some venoms is still unclear. In this study, we evaluated the interference of five isolated SVMPs in blood coagulation of humans, birds and small rodents. P-III class SVMPs (fractions Ic, IIb and IIc) possess gelatinolytic and hemorrhagic activities, and, of these, two also show fibrinolytic activity. P-I class SVMPs (fractions IVa and IVb) are only fibrinolytic. P-III class SVMPs reduced clotting time of human plasma. Fraction IIc was characterized as prothrombin activator and fraction Ic as factor X activator. In the absence of Ca2+, a firm clot was observed in chicken blood samples with fractions Ic, IIb and partially with fraction IIc. In contrast, without Ca2+, only fraction IIc was able to induce a firm clot in rat blood. In conclusion, functionally distinct forms of SVMPs were found in B. neuwiedi venom that affect distinct mechanisms in the coagulation system of humans, birds and small rodents. Distinct SVMPs appear to be more specialized to rat or chicken blood, strengthening the current hypothesis that toxin diversity enhances the possibilities of the snakes for hunting different prey or evading different predators. This functional diversity also impacts the complexity of human envenoming since different hemostatic mechanisms will be targeted by SVMPs accounting for the complexity of the response of humans to venoms.
Highlights
Venoms are trophic adaptations which allow venomous snakes to use potent toxins as a chemical means to subdue their prey [1]
The structural diversity of SVMPs was first confirmed in a pool of venoms collected from B. neuwiedi snakes kept under captivity
This assumption was first confirmed in this study in which the SVMPs isolated from B. neuwiedi venom were selective to different targets of the mammalian hemostatic system and acted with distinct potency on mammalian or bird blood
Summary
Venoms are trophic adaptations which allow venomous snakes to use potent toxins as a chemical means to subdue their prey [1] This efficient predation mechanism evolved in venomous snakes by recruitment of genes coding for physiological functions to the venom system in which they underwent duplications followed by neofunctionalization of the new copies under accelerated evolution [2,3,4,5]. It is reasonable to assume that the major protein families recruited to the venom apparatus have been selected by their efficiency to subdue prey [7] In this regard, venoms of elapid snakes and from certain viperid species are very efficient in prey paralysis and killing due to potent neurotoxins enclosed within three-finger toxins and phospholipases A2 (PLA2) protein families. In viperid venoms, the three-finger proteins are rare and PLA2s are not abundant while metalloproteinases, P-III class SVMPs
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