RESUMO
Cry11Aa and Cry11Ba are the two most potent toxins produced by mosquitocidal Bacillus thuringiensis subsp. israelensis and jegathesan, respectively. The toxins naturally crystallize within the host; however, the crystals are too small for structure determination at synchrotron sources. Therefore, we applied serial femtosecond crystallography at X-ray free electron lasers to in vivo-grown nanocrystals of these toxins. The structure of Cry11Aa was determined de novo using the single-wavelength anomalous dispersion method, which in turn enabled the determination of the Cry11Ba structure by molecular replacement. The two structures reveal a new pattern for in vivo crystallization of Cry toxins, whereby each of their three domains packs with a symmetrically identical domain, and a cleavable crystal packing motif is located within the protoxin rather than at the termini. The diversity of in vivo crystallization patterns suggests explanations for their varied levels of toxicity and rational approaches to improve these toxins for mosquito control.
Assuntos
Bacillus thuringiensis , Nanopartículas , Animais , Proteínas de Bactérias/toxicidade , Endotoxinas , Proteínas Hemolisinas/toxicidade , Larva , Controle de MosquitosRESUMO
In dehydrated rats, an early postingestive signal associated with the concentration of ingested fluid provides a signal that can inhibit neurohypophyseal vasopressin secretion. That inhibitory signal is not generated by the act of swallowing, as it is in dogs and many other animals, but by visceral osmoreceptors that presumably send a vagal signal to the nucleus of the solitary tract and the area postrema in the brain stem. In further contrast to dogs, the act of water ingestion does not provide an early signal inhibiting thirst in rats, but gastric emptying is so rapid that thirst can be satiated relatively quickly. When saline is consumed instead of water, thirst is inhibited by a different signal that results from the volume consumed and apparently is associated with gastrointestinal distension. These and other results emphasize the need to include gastric emptying of ingested fluid in considerations of water and Na(+) balance in rats.
