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Zhao W, Poncet-Legrand C, Staunton S, Quiquampoix H. pH-Dependent Changes in Structural Stabilities of Bt Cry1Ac Toxin and Contrasting Model Proteins following Adsorption on Montmorillonite. ENVIRONMENTAL SCIENCE & TECHNOLOGY 2023; 57:5693-5702. [PMID: 36989144 DOI: 10.1021/acs.est.2c09310] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/19/2023]
Abstract
The environmental fate of insecticidal Cry proteins, including time-dependent conservation of biological properties, results from their structural stability in soils. The complex cascade of reactions involved in biological action requires Cry proteins to be in solution. However, the pH-dependent changes in conformational stability and the adsorption-desorption mechanisms of Cry protein on soil minerals remain unclear. We used Derjaguin-Landau-Verwey-Overbeek (DLVO) calculation and differential scanning calorimetry to interpret the driving forces and structural stabilities of Cry1Ac and two contrasting model proteins adsorbed by montmorillonite. The structural stability of Cry1Ac is closer to that of the "hard" protein, α-chymotrypsin, than that of the "soft" bovine serum albumin (BSA). The pH-dependent adsorption of Cry1Ac and α-chymotrypsin could be explained by DLVO theory, whereas the BSA adsorption deviated from it. Patch-controlled electrostatic attraction, hydrophobic effects, and entropy changes following protein unfolding on a mineral surface could contribute to Cry1Ac adsorption. Cry1Ac, like chymotrypsin, was partly denatured on montmorillonite, and its structural stability decreased with an increase in pH. Moreover, small changes in the conformational heterogeneity of both Cry1Ac and chymotrypsin were observed following adsorption. Conversely, adsorbed BSA was completely denatured regardless of the solution pH. The moderate conformational rearrangement of adsorbed Cry1Ac may partially explain why the insecticidal activity of Bt toxin appears to be conserved in soils, albeit for a relatively short time period.
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Affiliation(s)
- Wenqiang Zhao
- Eco&Sols, INRAE, IRD, Cirad, Institut Agro, Univ Montpellier, 34090 Montpellier, France
- CAS Key Laboratory of Mountain Ecological Restoration and Bioresource Utilization and Ecological Restoration Biodiversity Conservation Key Laboratory of Sichuan Province, Chengdu Institute of Biology, Chinese Academy of Sciences, Chengdu 610041, China
| | | | - Siobhan Staunton
- Eco&Sols, INRAE, IRD, Cirad, Institut Agro, Univ Montpellier, 34090 Montpellier, France
| | - Hervé Quiquampoix
- Eco&Sols, INRAE, IRD, Cirad, Institut Agro, Univ Montpellier, 34090 Montpellier, France
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Dechkla M, Charoenjotivadhanakul S, Imtong C, Visitsattapongse S, Li HC, Angsuthanasombat C. Cry4Aa and Cry4Ba Mosquito-Active Toxins Utilize Different Domains in Binding to a Particular Culex ALP Isoform: A Functional Toxin Receptor Implicating Differential Actions on Target Larvae. Toxins (Basel) 2022; 14:toxins14100652. [PMID: 36287921 PMCID: PMC9607545 DOI: 10.3390/toxins14100652] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/17/2022] [Revised: 09/10/2022] [Accepted: 09/16/2022] [Indexed: 11/16/2022] Open
Abstract
The three-domain Cry4Aa toxin produced from Bacillus thuringiensis subsp. israelensis was previously shown to be much more toxic to Culex mosquito larvae than its closely related toxin—Cry4Ba. The interaction of these two individual toxins with target receptors on susceptible larval midgut cells is likely to be the critical determinant in their differential toxicity. Here, two full-length membrane-bound alkaline phosphatase (mALP) isoforms from Culex quinquefasciatus larvae, Cq-mALP1263and Cq-mALP1264, predicted to be GPI-linked was cloned and functionally expressed in Spodoptera frugiperda (Sf9) cells as 57- and 61-kDa membrane-bound proteins, respectively. Bioinformatics analysis disclosed that both Cq-mALP isoforms share significant sequence similarity to Aedes aegypti-mALP—a Cry4Ba toxin receptor. In cytotoxicity assays, Sf9 cells expressing Cq-mALP1264, but not Cq-mALP1263, showed remarkably greater susceptibility to Cry4Aa than Cry4Ba, while immunolocalization studies revealed that both toxins were capable of binding to each Cq-mALP expressed on the cell membrane surface. Molecular docking of the Cq-mALP1264-modeled structure with individual Cry4 toxins revealed that Cry4Aa could bind to Cq-mALP1264 primarily through particular residues on three surface-exposed loops in the receptor-binding domain—DII, including Thr512, Tyr513 and Lys514 in the β10-β11loop. Dissimilarly, Cry4Ba appeared to utilize only certain residues in its C-terminal domain—DIII to interact with such a Culex counterpart receptor. Ala-substitutions of selected β10-β11loop residues (T512A, Y513A and K514A) revealed that only the K514A mutant displayed a drastic decrease in biotoxicity against C. quinquefasciatus larvae. Further substitution of Lys514 with Asp (K514D) revealed a further decrease in larval toxicity. Furthermore, in silico calculation of the binding affinity change (ΔΔGbind) in Cry4Aa-Cq-mALP1264 interactions upon these single-substitutions revealed that the K514D mutation displayed the largest ΔΔGbind value as compared to three other mutations, signifying an adverse impact of a negative charge at this critical receptor-binding position. Altogether, our present study has disclosed that these two related-Cry4 mosquito-active toxins conceivably exploited different domains in functional binding to the same Culex membrane-bound ALP isoform—Cq-mALP1264 for mediating differential toxicity against Culex target larvae.
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Affiliation(s)
- Manussawee Dechkla
- Department of Environmental Biology, Faculty of Science and Technology, Suan Sunandha Rajabhat University, Bangkok 10300, Thailand
- Correspondence: (M.D.); (C.A.)
| | - Sathapat Charoenjotivadhanakul
- Bacterial Toxin Research Innovation Cluster (BRIC), Institute of Molecular Biosciences, Salaya Campus, Mahidol University, Nakorn Pathom 73170, Thailand
| | - Chompounoot Imtong
- Laboratory of Structural Biochemistry and Cell Chemical Biology, Biophysics Institute for Research and Development (BIRD), Fang, Chiang Mai 50110, Thailand
| | - Sarinporn Visitsattapongse
- Department of Biomedical Engineering, School of Engineering, King Mongkut’s Institute of Technology Ladkrabang, Ladkrabang, Bangkok 10520, Thailand
| | - Hui-Chun Li
- Department of Biochemistry, School of Medicine, Tzu Chi University, Hualien 97004, Taiwan
| | - Chanan Angsuthanasombat
- Bacterial Toxin Research Innovation Cluster (BRIC), Institute of Molecular Biosciences, Salaya Campus, Mahidol University, Nakorn Pathom 73170, Thailand
- Laboratory of Structural Biochemistry and Cell Chemical Biology, Biophysics Institute for Research and Development (BIRD), Fang, Chiang Mai 50110, Thailand
- Department of Biochemistry, School of Medicine, Tzu Chi University, Hualien 97004, Taiwan
- Correspondence: (M.D.); (C.A.)
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Complete structure elucidation of a functional form of the Bacillus thuringiensis Cry4Ba δ-endotoxin: Insights into toxin-induced transmembrane pore architecture. Biochem Biophys Res Commun 2022; 620:158-164. [DOI: 10.1016/j.bbrc.2022.06.065] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/29/2022] [Accepted: 06/21/2022] [Indexed: 11/24/2022]
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Thammasittirong A, Thammasittirong SNR, Imtong C, Charoenjotivadhanakul S, Sakdee S, Li HC, Okonogi S, Angsuthanasombat C. Bacillus thuringiensis Cry4Ba Insecticidal ToxinExploits Leu 615 in Its C-Terminal Domain to Interact with a Target Receptor- Aedes aegypti Membrane-Bound Alkaline Phosphatase. Toxins (Basel) 2021; 13:toxins13080553. [PMID: 34437424 PMCID: PMC8402544 DOI: 10.3390/toxins13080553] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/03/2021] [Revised: 07/27/2021] [Accepted: 08/03/2021] [Indexed: 11/16/2022] Open
Abstract
In addition to the receptor-binding domain (DII), the C-terminal domain (DIII) of three-domain Cry insecticidal δ-endotoxins from Bacillus thuringiensis has been implicated in target insect specificity, yet its precise mechanistic role remains unclear. Here, the 21 kDa high-purity isolated DIII fragment derived from the Cry4Ba mosquito-specific toxin was achieved via optimized preparative FPLC, allowing direct rendering analyses for binding characteristics toward its target receptor—Aedes aegypti membrane-bound alkaline phosphatase (Aa-mALP). Binding analysis via dotblotting revealed that the Cry4Ba-DIII truncate was capable of specific binding to nitrocellulose-bound Aa-mALP, with a binding signal comparable to its 65 kDa Cry4Ba-R203Q full-length toxin. Further determination of binding affinity via sandwich ELISA revealed that Cry4Ba-DIII exhibited a rather weak binding to Aa-mALP with a dissociation constant (Kd) of ≈1.1 × 10−7 M as compared with the full-length toxin. Intermolecular docking between the Cry4Ba-R203Q active toxin and Aa-mALP suggested that four Cry4Ba-DIII residues, i.e., Glu522, Asn552, Asn576, and Leu615, are potentially involved in such toxin–receptor interactions. Ala substitutions of each residue (E522A, N552A, N576A and L615A) revealed that only the L615A mutant displayed a drastic decrease in biotoxicity against A. aegypti larvae. Additional binding analysis revealed that the L615A-impaired toxin also exhibited a reduction in binding capability to the surface-immobilized Aa-mALP receptor, while two bio-inactive DII-mutant toxins, Y332A and F364A, which almost entirely lost their biotoxicity, apparently retained a higher degree of binding activity. Altogether, our data disclose a functional importance of the C-terminal domain of Cry4Ba for serving as a potential receptor-binding moiety in which DIII-Leu615 could conceivably be exploited for the binding to Aa-mALP, highlighting its contribution to toxin interactions with such a target receptor in mediating larval toxicity.
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Affiliation(s)
- Anon Thammasittirong
- Microbial Biotechnology Unit, Department of Microbiology, Faculty of Liberal Arts and Science, Kasetsart University, Nakhon Pathom 73140, Thailand;
- Correspondence: (A.T.); (C.A.)
| | - Sutticha Na-Ranong Thammasittirong
- Microbial Biotechnology Unit, Department of Microbiology, Faculty of Liberal Arts and Science, Kasetsart University, Nakhon Pathom 73140, Thailand;
| | - Chompounoot Imtong
- Faculty of Science and Technology, Prince of Songkla University, Pattani 94000, Thailand;
| | - Sathapat Charoenjotivadhanakul
- Bacterial Toxin Research Innovation Cluster (BRIC), Institute of Molecular Biosciences, Salaya Campus, Mahidol University, Nakorn Pathom 73170, Thailand; (S.C.); (S.S.)
| | - Somsri Sakdee
- Bacterial Toxin Research Innovation Cluster (BRIC), Institute of Molecular Biosciences, Salaya Campus, Mahidol University, Nakorn Pathom 73170, Thailand; (S.C.); (S.S.)
| | - Hui-Chun Li
- Department of Biochemistry, School of Medicine, Tzu Chi University, Hualien 97004, Taiwan;
| | - Siriporn Okonogi
- Research Center of Pharmaceutical Nanotechnology, Department of Pharmaceutical Sciences, Faculty of Pharmacy, Chiang Mai University, Chiang Mai 50200, Thailand;
| | - Chanan Angsuthanasombat
- Bacterial Toxin Research Innovation Cluster (BRIC), Institute of Molecular Biosciences, Salaya Campus, Mahidol University, Nakorn Pathom 73170, Thailand; (S.C.); (S.S.)
- Department of Biochemistry, School of Medicine, Tzu Chi University, Hualien 97004, Taiwan;
- Laboratory of Synthetic Biophysics and Chemical Biology, Biophysics Institute for Research and Development (BIRD), Chiang Mai 50130, Thailand
- Correspondence: (A.T.); (C.A.)
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Bourchookarn W, Bourchookarn A, Imtong C, Li HC, Angsuthanasombat C. His 180 in the pore-lining α4 of the Bacillus thuringiensis Cry4Aa δ-endotoxin is crucial for structural arrangements of the α4-α5 transmembrane hairpin and hence biotoxicity. BIOCHIMICA ET BIOPHYSICA ACTA-PROTEINS AND PROTEOMICS 2021; 1869:140634. [PMID: 33636413 DOI: 10.1016/j.bbapap.2021.140634] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Subscribe] [Scholar Register] [Received: 11/13/2020] [Revised: 02/15/2021] [Accepted: 02/19/2021] [Indexed: 10/22/2022]
Abstract
One proposed toxic mechanism of Bacillus thuringiensis Cry δ-endotoxins involves pore formation in target membranes by the α4-α5 transmembrane hairpin constituting their pore-forming domain. Here, nine selected charged and uncharged polar residues in the pore-lining α4 of the Cry4Aa mosquito-active toxin were substituted with Ala. All mutant toxins, i.e., D169A, R171A, Q173A, H178A, Y179A, H180A, Q182A, N183A and E187A, were over-expressed in Escherichia coli as 130-kDa protoxin inclusions at levels comparable to the wild-type toxin. Bioassays against Aedes aegypti larvae revealed that only H178A and H180A mutants displayed a drastic reduction in biotoxicity, albeit almost complete insolubility observed for H178A, but not for H180A inclusions. Further mutagenic analysis showed that replacements of His180 with charged (Arg, Lys, Asp, Glu), small uncharged polar (Ser, Cys) or small non-polar (Gly, Val) residues severely impaired the biotoxicity, unlike substitutions with relatively large uncharged (Asn, Gln, Leu) or aromatic (Phe, Tyr, Trp) residues. Similar to the trypsin-activated wild-type toxin, both bio-active and -inactive H180 mutants were still capable of releasing entrapped calcein from lipid vesicles and producing cation-selective channels with ~130-pS maximum conductance. Analysis of the Cry4Aa structure revealed the existence of a hydrophobic cavity near the critical His180 side-chain. Analysis of simulated structures revealed that His180-to-smaller residue conversions create a gap disrupting such cavity's hydrophobicity and hence structural arrangements of the α4-α5 hairpin. Altogether, our data disclose a critical involvement in Cry4Aa-biotoxicity of His180 exclusively present in the lumen-facing α4 for providing proper environment for the α4-α5 hairpin prior to membrane-inserted pore formation.
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Affiliation(s)
- Walairat Bourchookarn
- Faculty of Science and Technology, Prince of Songkla University, Pattani 94000, Thailand
| | - Apichai Bourchookarn
- Faculty of Science and Technology, Prince of Songkla University, Pattani 94000, Thailand.
| | - Chompounoot Imtong
- Faculty of Science and Technology, Prince of Songkla University, Pattani 94000, Thailand
| | - Hui-Chun Li
- Department of Biochemistry, School of Medicine, Tzu Chi University, Hualien 97004, Taiwan
| | - Chanan Angsuthanasombat
- Department of Biochemistry, School of Medicine, Tzu Chi University, Hualien 97004, Taiwan; Laboratory of Synthetic Biophysics and Chemical Biology, Biophysics Institute for Research and Development (BIRD), Chiang Mai 50230, Thailand; Bacterial Toxin Research Innovation Cluster (BRIC), Institute of Molecular Biosciences, Mahidol University, Salaya Campus, Nakornpathom 73170, Thailand.
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The C-Terminal Domain of the Bacillus thuringiensis Cry4Ba Mosquito-Specific Toxin Serves as a Potential Membrane Anchor. Toxins (Basel) 2019; 11:toxins11020062. [PMID: 30678087 PMCID: PMC6410236 DOI: 10.3390/toxins11020062] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/16/2018] [Revised: 01/15/2019] [Accepted: 01/18/2019] [Indexed: 11/16/2022] Open
Abstract
Although the C-terminal domain (DIII) of three-domain Cry insecticidal toxins from Bacillus thuringiensis has been implicated in various biological functions, its exact role still remains to be elucidated. Here, the 21-kDa isolated DIII fragment of the 65-kDa Cry4Ba mosquito-specific toxin was analyzed for its binding characteristics toward lipid-bilayer membranes. When the highly-purified Cry4Ba-DIII protein was structurally verified by attenuated total reflection Fourier transform infrared (ATR-FTIR) spectroscopy, it revealed the presence of a distinct β-sheet structure, corresponding to its structure embodied in the Cry4Ba crystal structure. Binding analysis via surface plasmon resonance (SPR) spectroscopy revealed that the 21-kDa Cry4Ba-DIII truncate displayed tight binding to immobilized liposome membranes in a two-step manner, exhibiting a dissociation rate constant (kd) comparable to the 65-kDa full-length toxin. Also similar to the Cry4Ba full-length toxin, its isolated DIII truncate was able to anchor a part of its molecule into the immobilized membrane as the SPR signal was still detected after prolonged treatment with proteinase K. However, unlike the full-length active toxin, the DIII truncate was unable to induce membrane permeability of calcein-loaded liposomes or ion-channel formation in planar lipid bilayers. Together, our present data have disclosed a pivotal role of C-terminal DIII in serving as a membrane anchor rather than a pore-forming moiety of the Cry4Ba mosquito-active toxin, highlighting its potential mechanistic contribution to the interaction of the full-length toxin with lipid membranes in mediating toxicity.
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Liu M, Liu R, Luo G, Li H, Gao J. Effects of Site-Mutations Within the 22 kDa No-Core Fragment of the Vip3Aa11 Insecticidal Toxin of Bacillus thuringiensis. Curr Microbiol 2017; 74:655-659. [DOI: 10.1007/s00284-017-1233-y] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/19/2017] [Accepted: 03/14/2017] [Indexed: 11/25/2022]
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