RESUMO

Bacillus thuringiensis subsp. israelensis (Bti) produces at least four different crystal proteins that are specifically toxic to different mosquito species and that belong to two non-related family of toxins, Cry and Cyt named Cry4Aa, Cry4Ba, Cry11Aa and Cyt1Aa. Cyt1Aa enhances the activity of Cry4Aa, Cry4Ba or Cry11Aa and overcomes resistance of Culex quinquefasciatus populations resistant to Cry11Aa, Cry4Aa or Cry4Ba. Cyt1Aa synergized Cry11Aa by their specific interaction since single point mutants on both Cyt1Aa and Cry11Aa that affected their binding interaction affected their synergistic insecticidal activity. In this work we show that Cyt1Aa loop ß6-αE K198A, E204A and ß7 K225A mutants affected binding and synergism with Cry4Ba. In addition, site directed mutagenesis showed that Cry4Ba domain II loop α-8 is involved in binding and in synergism with Cyt1Aa since Cry4Ba SI303-304AA double mutant showed decreased binding and synergism with Cyt1Aa. These data suggest that similarly to the synergism between Cry11Aa and Cyt1Aa toxins, the Cyt1Aa also functions as a receptor for Cry4Ba explaining the mechanism of synergism between these two Bti toxins.

Assuntos

Bacillus thuringiensis/metabolismo , Proteínas de Bactérias/metabolismo , Endotoxinas/metabolismo , Proteínas Hemolisinas/metabolismo , Inseticidas/metabolismo , Aedes/efeitos dos fármacos , Animais , Bacillus thuringiensis/genética , Toxinas de Bacillus thuringiensis , Proteínas de Bactérias/química , Proteínas de Bactérias/genética , Proteínas de Bactérias/farmacologia , Endotoxinas/química , Endotoxinas/genética , Endotoxinas/farmacologia , Ensaio de Imunoadsorção Enzimática , Proteínas Hemolisinas/química , Proteínas Hemolisinas/genética , Proteínas Hemolisinas/farmacologia , Inseticidas/farmacologia , Mutagênese Sítio-Dirigida , Ligação Proteica/genética , Ligação Proteica/fisiologia , Estrutura Secundária de Proteína