DM43 AND DM64, TWO IMMUNOGLOBULIN-LIKE PROTEINS FROM Didelphis marsupialis SERUM WITH ANTIHEMORRHAGIC OR ANTIMYOTOXIC ACTIVITY

PERALES, J.(1)

(1)Departamentode Fisiologia e Farmacodinâmica, IOC, FIOCRUZ, Rio de Janeiro.

Natural resistance to snake venom toxic effects is observed in some animals and, in many cases, this is due to the presence of soluble neutralizing proteins in their sera. Our group has isolated several of these neutralizing factors from the sera of some mammals and snakes. From the opossum (Didelphis marsupialis) serum, we have isolated and characterized three of them. Two (DM40 and DM43), with antihemorrhagic activity, and the other one (DM64), with antimyotoxic activity. In spite of these different activities, they have some similar characteristics, they are acidic glycoproteins, homodimeric under native conditions and, the most important, they present immunoglobulin-like structure. The complete amino acid sequences of DM43 and DM64 showed 78% similarity. However, DM43 has three immunoglobulin-like domains, while DM64 has five. DM43 and DM40 inhibited the enzymatic activity of several snake venom metalloproteinases (SVMP), such as jararhagin and bothrolysinand formed stable inactive non-covalent complexes with them. DM64 was able neither to inhibit these SVMPs nor to form complexes with them. On the other hand, DM64 neutralized both the in vivo myotoxicity and the in vitro cytotoxicity of myotoxins I (mt-I/Asp⁴⁹) and II (mt-II/Lys⁴⁹) from B.asper venom. The inhibitor formed non-covalent complexes with both toxins, but did not inhibit the PLA₂ activity of mt-I. Accordingly, DM64 did not neutralize the anticoagulant effect of mt-I nor its intracerebroventricular lethality, effects that depend on its enzymatic activity, which demonstrates the dissociation between the catalytic and toxic activities of this Asp⁴⁹ myotoxicPLA₂. Furthermore, despite its similarity with the metalloproteinase inhibitors DM43 and DM40, these proteins did not present any antimyotoxicactivity against mt-I or mt-II and did not form complexes with them. We recently postulated that the difference between the activities of these two homologous proteins is probably consequence of the presence of either three or five immunoglobulin-like domains and/or other important structural differences, such as the presence of gaps and residues substitutions.

CORRESPONDENCE TO:

Jonas EnriquePeralesAguilar, Rua Eneida de Morais 276, Apartamento 105, Rio de Janeiro, RJ, CEP: 21920-230, Brasil, Email: jperales@ioc.fiocruz.br