Entomotoxic action of Sambucus nigra agglutinin i in Acyrthosiphon pisum aphids and Spodoptera exigua caterpillars through caspase‐3‐like‐dependent apoptosis

In this project, the toxicity and mechanism of action of the ricin‐B‐related lectin SNA‐I from elderberry (Sambucus nigra) in the pea aphid (Acyrthosiphon pisum) and the beet armyworm (Spodoptera exigua), two important pest insects in agriculture, were studied. SNA‐I is a chimeric lectin belonging to the class of ribosome‐inactivating proteins and consists of an A‐chain with N‐glycosidase activity and a carbohydrate‐binding B‐chain. Incorporation of 2 mg/ml of SNA‐I in the diet of neonates and adults of A. pisum caused 40–46% mortality within 2 days, while in third instars of S. exigua, the larval biomass was significantly reduced by 12% after feeding for 3 days on a diet containing 5 mg/g of SNA‐I. Interestingly, extracts of the (mid)gut of treated A. pisum and S. exigua demonstrated DNA fragmentation and this was accompanied with an increase in caspase‐3‐like activity. The involvement of cell death or apoptosis in the entomotoxicity of SNA‐I through induction of caspase‐3‐like activity was also confirmed by addition of the permeable caspase‐3 inhibitor III in the diet, leading to a rescue of the treated aphid neonates. Finally, similar to the chimeric lectin SNA‐I, the hololectin SNA‐II, consisting of two carbohydrate‐binding B‐chains caused high mortality to neonate A. pisum aphids with an LC₅₀ of 1.59 mg/ml, suggesting that the entomotoxic action of the lectins under study mainly relies on their carbohydrate‐binding activity. © 2010 Wiley Periodicals, Inc.     

Translation of honeybee promelittin messenger RNA. Formation of a larger product in a mammalian cell-free system.

Venom glands of honeybees synthesize the peptide melittin via the precursor promelittin. Total RNA preparations from venom glands served as template in a cell-free system prepared from mammalian cells. The heterologous system translated the insect mRNA with approximately the same efficiency as hemoglobin mRNA. A polypeptide was synthesized which, as shown by acrylamide gel electrophoresis in the presence of detergent, has a higher molecular weight than promelittin. Analysis of peptic fragments as well as Edman degradation have demonstrated that sequences characteristic of venom gland promelittin are present in this product formed in vitro. Furthermore, a bacterial protease which specifically splits after acidic residues liberates from the cell-free product a fragment which closely resembles melittin. Evidence is presented that most of the extra amino acids are located at the amino terminus of the product formed in vitro. The larger polypeptide detected in vitro may represent a precursor of promelittin.