Influência do domínio ligante em quitina de uma quitinase de Bacillus thuringiensis sobre sua atividade enzimática e ação inseticida sobre Diatraea saccharalis (Fabricius, 1794) (Lepidoptera: Crambidae)
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Data
2018-05-14
Autores
Augusto, Maria Laura Viola [UNESP]
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Universidade Estadual Paulista (Unesp)
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O controle da broca da cana, Diatraea saccharalis (Fabricius, 1794) (Lepidoptera: Crambidae), pode ser feito pela aplicação de inseticidas químicos, mas o uso dessa tática de manejo pode resultar em danos ambientais e ao homem. De forma alternativa e com efeitos negativos reduzidos, o manejo de D. saccharalis e outros insetos-praga pode ser feito pela utilização do entomopatógeno Bacillus thuringiensis. Além do uso de formulações de B. thuringiensis para o controle de pragas, um ou mais genes que codificam proteínas inseticidas Cry e Vip de B. thuringiensis estão presentes nas plantas transgênicas com resistência a insetos comercialmente disponíveis no Brasil. Apesar de alta adoção, efeitos colaterais reduzidos e eficiência das plantas Bt, o uso desta tecnologia pode resultar na seleção de populações de insetos resistentes às plantas transgênicas. Por isso, a busca por novas proteínas e combinações de proteínas com diferentes modos de ação para retardar a evolução da resistência deve ser constante. Nesse cenário, uma quitinase de B. thuringiensis apresenta potencial para ser incorporada em uma nova geração de plantas transgênicas. Quitinases são enzimas que apresentam domínios catalíticos para hidrólise de quitina e domínios ligantes em quitina (CBD) que podem estar envolvidos com a atividade inseticida. A atividade inseticida das quitinases é relacionada com a desestruturação da membrana peritrófica dos insetos e consequente perda de suas propriedades e funções. Além da descoberta de proteínas inseticidas com diferentes modos de ação, é de interesse que essas apresentem interações positivas com outras proteínas inseticidas. No presente trabalho, duas formas de uma quitinase de B. thuringiensis - ChiΔSP (sem o peptídio sinal) e ChiΔSP.CBD (sem o peptídio sinal e sem o domínio ligante em quitina) - foram produzidas de forma heteróloga em Escherichia coli para avaliações bioquímicas e biológicas sobre D. saccharalis. Ensaios bioquímicos das enzimas ChiΔSP e ChiΔSP.CBD indicam que a atividade quitinolítica sobre quitina coloidal de ChiΔSP (3,07±0,15 U/nmol) foi maior que de ChiΔSP.CBD (1,83±0,06 U/nmol), a ligação de ChiΔSP à quitina coloidal também foi superior à ligação de ChiΔSP.CBD e as maiores atividades (60-100% da atividade total) de ChiΔSP e ChiΔSP.CBD foram detectadas a 30 e 40°C em uma ampla faixa de pH (4,0-9,0). Após estimar a CL50 da proteína Vip3Aa42 sobre lagartas neonatas de D. saccharalis em 352,132 ng/cm2 de dieta, foram avaliadas interações entre Vip3Aa42 e ChiΔSP ou ChiΔSP.CBD. Os resultados indicam que a adição isolada de 2,41 nmol/cm2 de ChiΔSP ou ChiΔSP.CBD não resultou na mortalidade de lagartas de D. saccharalis. A combinação da CL50 de Vip3Aa42 com 2,41 nmol/cm2 de ChiΔSP apresentou efeito sinérgico para mortalidade das lagartas (mortalidade de 90%), mas nenhum efeito (aditivo, sinérgico ou antagônico) foi observado para a combinação da CL50 de Vip3Aa42 com 2,41 nmol/cm2 de ChiΔSP.CBD. A ausência do CBD em ChiΔSP.CBD e consequentes alterações bioquímicas impediu sinergismo de ChiΔSP.CBD com Vip3Aa42 sobre lagartas de D. saccharalis.
Chemical control is applied to manage the sugarcane borer, Diatraea saccharalis (Fabricius, 1794) (Lepidoptera: Crambidae). However, this control tactic may result in great damages to the environment and non-target species, including men. Alternativelly, the use of the entomopathogen Bacillus thuringiensis can be made to manage D. saccharalis and other insect pests with reduced undisarable side effects. Beyond the use of formulations of B. thuringiensis for pest control, one or more genes of insecticidal proteins from B. thuringiensis such as Cry and Vip are incorporated into commercially available transgenic plants with insect resistance in Brazil. Despite of the high adoption rate, reduced side effects, and high efficency, the intensive use of this technology may result in the selection of insect-resistant populations to transgenic plants. For this reason, the search for new genes with different modes of action to delay the evolution of resistance must be constant. In this scenario, a chitinase from B. thuringiensis has potential to be incorporated into a new generation of transgenic plants. Chitinases are enzymes of the family of glycosyl hydrolases which catalyze the hydrolysis of chitin. Chitinases present catalytic domains responsible for the hydrolysis of chitin and chitin-binding domains (CBD), both associated to insecticidal activity. Insecticidal activity of chitinases is related to the disruption of the peritrophic membrane of insects, which results in the loss of properties and functions of this structure. In addition to the discovery of insecticidal proteins with different modes of action, positive interactions with other insecticidal proteins is desirable for pest management. In the present work, two forms of a chitinase of B. thuringiensis - ChiΔSP (without signal peptide) and ChiΔSP.CBD (without signal peptide and without the chitin-binding domain) - were produced by heterologous expression in Escherichia coli for biochemical and biological analyses. Chitinolytic activity of ChiΔSP (3.07 ± 0.15 U/nmol) was higher than that observed for ChiΔSP.CBD (1.83 ± 0.06 U/nmol) towards colloidal chitin. The binding of ChiΔSP to colloidal chitin was also higher than that observed for ChiΔSP.CBD, and the ChiΔSP or ChiΔSP.CBD chitinolytic activity (60-100% of total chitinolytic activity) was detected at 30 and 40°C in a broad pH range (4.0-9.0). After estimating the LC50 of the Vip3Aa42 protein at 352,132 ng/cm2 of diet, interactions between combinations of Vip3Aa42 and ChiΔSP or ChiΔSP.CBD were evaluated. Results indicate that the adition of 2,41 nmol/cm2 of ChiΔSP or ChiΔSP.CBD do not result in larval mortality of D. saccharalis. The combination of the LC50 of Vip3Aa42 with 2,41 nmol/cm2 nmol of ChiΔSP resulted in a synergic effect (mortality of 90%), but no effect (aditive, sinergic or antagonic) was observed when the LC50 of Vip3Aa42 was combined to 2,41 nmol/cm2 nmol of ChiΔSP.CBD. Lack of CBD in ChiΔSP.CBD resulted in biochemical changes in this form of B. thuringiensis chitinase which impacted on the sinergic effect of this protein with Vip3Aa42 against D. saccharalis.
Chemical control is applied to manage the sugarcane borer, Diatraea saccharalis (Fabricius, 1794) (Lepidoptera: Crambidae). However, this control tactic may result in great damages to the environment and non-target species, including men. Alternativelly, the use of the entomopathogen Bacillus thuringiensis can be made to manage D. saccharalis and other insect pests with reduced undisarable side effects. Beyond the use of formulations of B. thuringiensis for pest control, one or more genes of insecticidal proteins from B. thuringiensis such as Cry and Vip are incorporated into commercially available transgenic plants with insect resistance in Brazil. Despite of the high adoption rate, reduced side effects, and high efficency, the intensive use of this technology may result in the selection of insect-resistant populations to transgenic plants. For this reason, the search for new genes with different modes of action to delay the evolution of resistance must be constant. In this scenario, a chitinase from B. thuringiensis has potential to be incorporated into a new generation of transgenic plants. Chitinases are enzymes of the family of glycosyl hydrolases which catalyze the hydrolysis of chitin. Chitinases present catalytic domains responsible for the hydrolysis of chitin and chitin-binding domains (CBD), both associated to insecticidal activity. Insecticidal activity of chitinases is related to the disruption of the peritrophic membrane of insects, which results in the loss of properties and functions of this structure. In addition to the discovery of insecticidal proteins with different modes of action, positive interactions with other insecticidal proteins is desirable for pest management. In the present work, two forms of a chitinase of B. thuringiensis - ChiΔSP (without signal peptide) and ChiΔSP.CBD (without signal peptide and without the chitin-binding domain) - were produced by heterologous expression in Escherichia coli for biochemical and biological analyses. Chitinolytic activity of ChiΔSP (3.07 ± 0.15 U/nmol) was higher than that observed for ChiΔSP.CBD (1.83 ± 0.06 U/nmol) towards colloidal chitin. The binding of ChiΔSP to colloidal chitin was also higher than that observed for ChiΔSP.CBD, and the ChiΔSP or ChiΔSP.CBD chitinolytic activity (60-100% of total chitinolytic activity) was detected at 30 and 40°C in a broad pH range (4.0-9.0). After estimating the LC50 of the Vip3Aa42 protein at 352,132 ng/cm2 of diet, interactions between combinations of Vip3Aa42 and ChiΔSP or ChiΔSP.CBD were evaluated. Results indicate that the adition of 2,41 nmol/cm2 of ChiΔSP or ChiΔSP.CBD do not result in larval mortality of D. saccharalis. The combination of the LC50 of Vip3Aa42 with 2,41 nmol/cm2 nmol of ChiΔSP resulted in a synergic effect (mortality of 90%), but no effect (aditive, sinergic or antagonic) was observed when the LC50 of Vip3Aa42 was combined to 2,41 nmol/cm2 nmol of ChiΔSP.CBD. Lack of CBD in ChiΔSP.CBD resulted in biochemical changes in this form of B. thuringiensis chitinase which impacted on the sinergic effect of this protein with Vip3Aa42 against D. saccharalis.
Descrição
Palavras-chave
Atividade quitinolítica, Broca da cana, Sinergismo, Toxinas inseticidas, Chitinolytic activity, Sugarcane borer, Insecticidal toxins, Synergism