Gm-TX, a new toxic protein from soybean (Glycine max) seeds with potential for controlling insect pests

A novel toxic protein from Glycine max seeds, named Gm-TX, was purified by combination of differential precipitation with ammonium sulphate, DEAE-cellulose, anhydrotrypsin-sepharose 4B and Superdex 200 HR fast-protein liquid chromatography.Gm-TX is composed of one polypeptide chain of 28 kDa (SDS-PAGE), with pI 5.1–5.2, contains <0.5% neutral sugar, has N-terminal sequence comprised of KTISSEDSPFFNCREK, maximum absorption spectrum at 280 nm and molar extinction coefficient of 16.9. It exhibited ribonuclease activity (1821.42 ± 3.34 UA/h/mgP) toward yeast RNA and promoted rabbit erythrocyte agglutination (120.4 HU/mgP) mediated by anti-Gm-TX IgG, which was inhibited by mannose. It was devoid of trypsin inhibitory, urease and chitinase activities. Gm-TX was lethal to mice by intraperitoneal route with LD50 of 4.5 mg/kg. Moreover, it showed dose-dependent insecticidal activity on the major economically important pests Callosobruchus maculatus and Dysdercus peruvianus, producing ca. 50% and 56% mortality when incorporated into artificial diets at a level of 1.16% and 0.25%, respectively. These data indicate that Gm-TX is a candidate protein that could be expressed in genetically transformed plants for improved resistance to insect pests.