Scorpion venoms are composed of a number of peptides, many of which show neurotoxicity. In addition to these neurotoxins, several antimicrobial peptides have also been isolated from the venoms. The scorpion Isometrus maculatus, belonging to the Buthidae family, is found in many tropical regions including Japan, but little attention has been paid to its biological activity and chemical composition. In this study, we isolated a novel insect toxin, Im-1, by bioassay-guided fractionation of the venom of I. maculatus. Rapid and reversible paralysis was observed after injection of Im-1 into crickets. Im-1 consists of 56 amino acids, and is predicted to form an amphipathic alpha-helix. Since Im-1 shares sequence similarity to an antimicrobial peptide, parabutoporin, we evaluated its effects on several bacterial strains and found that it showed an antimicrobial activity profile similar to parabutoporin. This suggests that Im-1 and parabutoporin exert their antimicrobial effects through similar mechanisms.
In vitro-transcribed, unmodified, and non-aminoacylated amber suppressor tRNAs that are recognized by natural aminoacyl-tRNA synthetase were improved toward higher suppression efficiency in batch-mode cell-free translation in wheat germ extract. The suppression efficiency of the suppressor obtained through four sequence optimization steps (anticodon alteration of natural tRNAs (the first generation); chimerization of the efficient suppressors in the first generation; investigation and optimization of the effective parts in the second generation; combination of the optimized parts in the third generation) and by the terminal tuning was approximately 60%, which was 2.4-fold higher than that of the best suppressor in the first generation. In addition, an eRF1 aptamer further increased the efficiency up to 85%. This highly efficient suppression system also functioned well in a dialysis-based large-scale protein synthesis.
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