Bothrops
snake venoms are known to induce local tissue damage such as
hemorrhage and myonecrosis. The opossum Didelphis marsupialis is resistant to these
snake venoms and has natural
venom inhibitors in its plasma. The aim of this work was to clone and study the chemical, physicochemical and
biological properties of DM64, an antimyotoxic
protein from opossum serum. DM64 is an acidic
protein showing 15% glycosylation and with a molecular mass of 63 659 Da when analysed by MALDI-TOF MS. It was cloned and the amino acid sequence was found to be homologous to DM43, a
metalloproteinase inhibitor from D. marsupialis serum, and to human alpha1B-glycoprotein, indicating the presence of five immunoglobulin-like domains. DM64 neutralized both the in vivo
myotoxicity and the in vitro cytotoxicity of
myotoxins I (mt-I/Asp49) and II (mt-II/Lys49) from Bothrops asper
venom. The inhibitor formed noncovalent 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, and which demonstrate the dissociation between the catalytic and toxic activities of this Asp49 myotoxic PLA2. Furthermore, despite its similarity with
metalloproteinase inhibitors, DM64 presented no
antihemorrhagic activity against Bothrops jararaca or Bothrops asper crude
venoms, and did not inhibit the fibrinogenolytic activity of
jararhagin or bothrolysin. This is the first report of a
myotoxin inhibitor with an
immunoglobulin-like structure isolated and characterized from animal blood.