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Khorramnejad A, Domínguez-Arrizabalaga M, Caballero P, Escriche B, Bel Y. Study of the Bacillus thuringiensis Cry1Ia Protein Oligomerization Promoted by Midgut Brush Border Membrane Vesicles of Lepidopteran and Coleopteran Insects, or Cultured Insect Cells. Toxins (Basel) 2020; 12:toxins12020133. [PMID: 32098045 PMCID: PMC7076784 DOI: 10.3390/toxins12020133] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/16/2019] [Revised: 01/31/2020] [Accepted: 02/19/2020] [Indexed: 12/18/2022] Open
Abstract
Bacillus thuringiensis (Bt) produces insecticidal proteins that are either secreted during the vegetative growth phase or accumulated in the crystal inclusions (Cry proteins) in the stationary phase. Cry1I proteins share the three domain (3D) structure typical of crystal proteins but are secreted to the media early in the stationary growth phase. In the generally accepted mode of action of 3D Cry proteins (sequential binding model), the formation of an oligomer (tetramer) has been described as a major step, necessary for pore formation and subsequent toxicity. To know if this could be extended to Cry1I proteins, the formation of Cry1Ia oligomers was studied by Western blot, after the incubation of trypsin activated Cry1Ia with insect brush border membrane vesicles (BBMV) or insect cultured cells, using Cry1Ab as control. Our results showed that Cry1Ia oligomers were observed only after incubation with susceptible coleopteran BBMV, but not following incubation with susceptible lepidopteran BBMV or non-susceptible Sf21 insect cells, while Cry1Ab oligomers were persistently detected after incubation with all insect tissues tested, regardless of its host susceptibility. The data suggested oligomerization may not necessarily be a requirement for the toxicity of Cry1I proteins.
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Affiliation(s)
- Ayda Khorramnejad
- Departamento de Genética/ERI BioTecMed, Universitat de València, Burjassot, 46100 València, Spain; (A.K.); (B.E.)
- Department of Plant Protection, College of Agriculture and Natural Resources, University of Tehran, Karaj 31578-77871, Alborz, Iran
| | - Mikel Domínguez-Arrizabalaga
- Departamento de Agronomía, Biotecnología y Alimentación, Universidad Pública de Navarra, Pamplona, 31006 Navarra, Spain; (M.D.-A.); (P.C.)
| | - Primitivo Caballero
- Departamento de Agronomía, Biotecnología y Alimentación, Universidad Pública de Navarra, Pamplona, 31006 Navarra, Spain; (M.D.-A.); (P.C.)
| | - Baltasar Escriche
- Departamento de Genética/ERI BioTecMed, Universitat de València, Burjassot, 46100 València, Spain; (A.K.); (B.E.)
| | - Yolanda Bel
- Departamento de Genética/ERI BioTecMed, Universitat de València, Burjassot, 46100 València, Spain; (A.K.); (B.E.)
- Correspondence:
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Xu L, Pan ZZ, Zhang J, Niu LY, Li J, Chen Z, Liu B, Zhu YJ, Chen QX. Exposure of helices α4 and α5 is required for insecticidal activity of Cry2Ab by promoting assembly of a prepore oligomeric structure. Cell Microbiol 2018; 20:e12827. [PMID: 29380507 DOI: 10.1111/cmi.12827] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/17/2017] [Revised: 01/15/2018] [Accepted: 01/17/2018] [Indexed: 12/15/2022]
Abstract
Cry2Ab, a pore-forming toxin derived from Bacillus thuringiensis, is widely used as a bio-insecticide to control lepidopteran pests around the world. A previous study revealed that proteolytic activation of Cry2Ab by Plutella xylostella midgut juice was essential for its insecticidal activity against P. xylostella, although the exact molecular mechanism remained unknown. Here, we demonstrated for the first time that proteolysis of Cry2Ab uncovered an active region (the helices α4 and α5 in Domain I), which was required for the mode of action of Cry2Ab. Either the masking or the removal of helices α4 and α5 mediated the pesticidal activity of Cry2Ab. The exposure of helices α4 and α5 did not facilitate the binding of Cry2Ab to P. xylostella midgut receptors but did induce Cry2Ab monomer to aggregate and assemble a 250-kDa prepore oligomer. Site-directed mutagenesis assay was performed to generate Cry2Ab mutants site directed on the helices α4 and α5, and bioassays suggested that some Cry2Ab variants that could not form oligomers had significantly lowered their toxicities against P. xylostella. Taken together, our data highlight the importance of helices α4 and α5 in the mode of action of Cry2Ab and could lead to more detailed studies on the insecticidal activity of Cry2Ab.
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Affiliation(s)
- Lian Xu
- State Key Laboratory of Cellular Stress Biology, Key Laboratory of the Ministry of Education for Coastal and Wetland Ecosystems, School of Life Sciences, Xiamen University, Xiamen, Fujian, People's Republic of China
| | - Zhi-Zhen Pan
- Agricultural Bio-Resources Research Institute, Fujian Academy of Agricultural Sciences, Fuzhou, Fujian, People's Republic of China
| | - Jing Zhang
- State Key Laboratory of Cellular Stress Biology, Key Laboratory of the Ministry of Education for Coastal and Wetland Ecosystems, School of Life Sciences, Xiamen University, Xiamen, Fujian, People's Republic of China
| | - Li-Yang Niu
- State Key Laboratory of Cellular Stress Biology, Key Laboratory of the Ministry of Education for Coastal and Wetland Ecosystems, School of Life Sciences, Xiamen University, Xiamen, Fujian, People's Republic of China
| | - Jie Li
- State Key Laboratory of Cellular Stress Biology, Key Laboratory of the Ministry of Education for Coastal and Wetland Ecosystems, School of Life Sciences, Xiamen University, Xiamen, Fujian, People's Republic of China
| | - Zheng Chen
- Agricultural Bio-Resources Research Institute, Fujian Academy of Agricultural Sciences, Fuzhou, Fujian, People's Republic of China
| | - Bo Liu
- Agricultural Bio-Resources Research Institute, Fujian Academy of Agricultural Sciences, Fuzhou, Fujian, People's Republic of China
| | - Yu-Jing Zhu
- Agricultural Bio-Resources Research Institute, Fujian Academy of Agricultural Sciences, Fuzhou, Fujian, People's Republic of China
| | - Qing-Xi Chen
- State Key Laboratory of Cellular Stress Biology, Key Laboratory of the Ministry of Education for Coastal and Wetland Ecosystems, School of Life Sciences, Xiamen University, Xiamen, Fujian, People's Republic of China
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