Echinhibin-1 - an inhibitor of Sendai virus isolated from the venom of the snake Echis coloratus

The snake venom of Echis coloratus was found to abolish the hemagglutinating activity, hemolytic activity and in vivo infectivity of Sendai virus. The active factor (Echinhibin-1) was purified by gel filtration on Sephadex G-50, followed by chromatography on DEAE-Sepharose and CM-Sepharose. Echinhibin-1 is a protease with a molecular weight of about 25 kDa, an isoelectric point of 7 and is stained by PAS, indicating that it is a glycoprotein. It showed a strong azocollase activity that was stable up to 68°C and at pH values of 4.5-10.5. Ten μg/ml were sufficient to abolish the hemolytic effect of the virus on human erythocytes when inculbation was at 37°C for 2 h, while 20 μg/ml abolished the hemagglutinating activity. Addition of Echinhibin-1 after the adsorption of Sendai virions onto washed erythrocytes at 4 °C did not inhibit the subsequently hemolytic activity at 37 °C, indicating that Echinhibin-1 interferes with virus adsorption to the cells. Of various protease inhibitors, only Na₂ EDTA and o-phenanthroline inhibited the antiviral activity of the purified factor, indicating that it is a metalloproteinase. In vivo, mice inoculated intranasally with the virus pretreated with Echinhibin-1 developed well and gained weight, whereas untreated virus-infected mice lost weight and died within 1 week. Intravenous administrations of the purified factor up to 80 μg/mouse produced no signs of toxicity and subcutaneous injections caused no hemorrhagic activity, while the whole venom is very hemorrhagic with an LD₅₀ of 250 μg/kg for mice.