Three toxins with phospholipase activity isolated from the yellow-legged hornet ( Vespa verutina) venom

Abstract

The yellow-legged hornet, Vespa verutina, is widely distributed in both the mountain area and the suburbs of Taiwan and possesses highly toxic venom (LD 50=0.02 μl/g mouse). By gel filtration on Fractogel (TSK HW 50f) followed by cation-exchange chromatography on Mono S column, three toxins designated as verutoxin 1, 2a and 2b (VT-1, VT-2a and VT-2b) were isolated from the venom. The toxin VT-1 had a molecular mass of 34,982 Da and an LD 50 value of 3.61 μg/g mouse. Toxin VT-2a and 2b were more basic and more toxic than VT-1. VT-2a and 2b were isotoxins with molecular masses differing in only 14 Da (33,360 and 33,374 Da, respectively) and had a similar toxicity in mice (LD 50=0.87 μg/g mouse). All three toxins were capable of catalyzing the hydrolysis of emulsified phospholipids and lysophosphatide, but not sphingomyelin. Analysis of the hydrolyzed products (fatty acid and lyso-compound) by a liquid chromatography/mass spectrometer revealed that the toxins liberates fatty acid mainly from the 1-position of the synthetic phospholipid. This result indicates that verutoxins possess phospholipase A 1 activity. Toxin VT-1 showed higher phospholipase activity than VT-2a and 2b. However, the latter toxins exhibited much higher direct hemolytic activity toward the mouse red blood cells. Vespid phospholipases are known as one of the three major venom allergens in many species of wasps. Our studies indicate that vespid phospholipases A 1, in addition to acting as allergens, possess direct toxic actions that may also cause death in animals. Toxin VT-2a and 2b which possess potent hemolytic activity and high lethality in mice may act as the lethal factor of V. verutina venom.