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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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Chandra Ojha S, Imtong C, Meetum K, Sakdee S, Katzenmeier G, Angsuthanasombat C. Purification and characterization of the antibacterial peptidase lysostaphin from Staphylococcus simulans : Adverse influence of Zn 2+ on bacteriolytic activity. Protein Expr Purif 2018; 151:106-112. [DOI: 10.1016/j.pep.2018.06.013] [Citation(s) in RCA: 13] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/22/2018] [Revised: 06/15/2018] [Accepted: 06/22/2018] [Indexed: 02/06/2023]
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Kaikaew A, Promptmas C, Angsuthanasombat C. Importance of Thr328 and Thr369 for functional maintenance of two receptor-binding β-hairpins of the Bacillus thuringiensis Cry4Ba toxin: Implications for synergistic interactions with Cyt2Aa2. Biochem Biophys Res Commun 2016; 469:698-703. [DOI: 10.1016/j.bbrc.2015.11.115] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/16/2015] [Accepted: 11/25/2015] [Indexed: 10/22/2022]
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Sriwimol W, Aroonkesorn A, Sakdee S, Kanchanawarin C, Uchihashi T, Ando T, Angsuthanasombat C. Potential Prepore Trimer Formation by the Bacillus thuringiensis Mosquito-specific Toxin: MOLECULAR INSIGHTS INTO A CRITICAL PREREQUISITE OF MEMBRANE-BOUND MONOMERS. J Biol Chem 2015; 290:20793-20803. [PMID: 26112409 DOI: 10.1074/jbc.m114.627554] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/20/2014] [Indexed: 12/31/2022] Open
Abstract
The insecticidal feature of the three-domain Cry δ-endotoxins from Bacillus thuringiensis is generally attributed to their capability to form oligomeric pores, causing lysis of target larval midgut cells. However, the molecular description of their oligomerization process has not been clearly defined. Here a stable prepore of the 65-kDa trypsin-activated Cry4Ba mosquito-specific toxin was established through membrane-mimetic environments by forming an ∼200-kDa octyl-β-D-glucoside micelle-induced trimer. The SDS-resistant trimer caused cytolysis to Sf9 insect cells expressing Aedes-mALP (a Cry4Ba receptor) and was more effective than a toxin monomer in membrane perturbation of calcein-loaded liposomes. A three-dimensional model of toxin trimer obtained by negative-stain EM in combination with single-particle reconstruction at ∼5 nm resolution showed a propeller-shaped structure with 3-fold symmetry. Fitting the three-dimensional reconstructed EM map with a 100-ns molecular dynamics-simulated Cry4Ba structure interacting with an octyl-β-D-glucoside micelle showed relative positioning of individual domains in the context of the trimeric complex with a major protrusion from the pore-forming domain. Moreover, high-speed atomic force microscopy imaging at nanometer resolution and a subsecond frame rate demonstrated conformational transitions from a propeller-like to a globularly shaped trimer upon lipid membrane interactions, implying prepore-to-pore conversion. Real-time trimeric arrangement of monomers associated with L-α-dimyristoylphosphatidylcholine/3-[(3-cholamidopropyl)dimethylammonio]-2-hydroxy-1-propanesulfonic acid bicelle membranes was also envisaged by successive high-speed atomic force microscopy imaging, depicting interactions among three individual subunits toward trimer formation. Together, our data provide the first pivotal insights into the structural requirement of membrane-induced conformational changes of Cry4Ba toxin monomers for the molecular assembly of a prepore trimer capable of inserting into target membranes to generate a lytic pore.
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Affiliation(s)
- Wilaiwan Sriwimol
- Department of Clinical Chemistry, Faculty of Medical Technology, Mahidol University, Nakornpathom 73170, Thailand; Department of Bacterial Protein Toxin Research Cluster, Institute of Molecular Biosciences, Mahidol University, Nakornpathom 73170, Thailand
| | - Aratee Aroonkesorn
- Department of Bacterial Protein Toxin Research Cluster, Institute of Molecular Biosciences, Mahidol University, Nakornpathom 73170, Thailand
| | - Somsri Sakdee
- Department of Bacterial Protein Toxin Research Cluster, Institute of Molecular Biosciences, Mahidol University, Nakornpathom 73170, Thailand
| | - Chalermpol Kanchanawarin
- Laboratory of Theoretical and Computational Biophysics, Department of Physics, Faculty of Science, Kasetsart University, Bangkok 10900, Thailand
| | - Takayuki Uchihashi
- Department of Physics and Bio-AFM Frontier Research Center, Kanazawa University, Kanazawa, Ishikawa 920-1192, Japan
| | - Toshio Ando
- Department of Physics and Bio-AFM Frontier Research Center, Kanazawa University, Kanazawa, Ishikawa 920-1192, Japan
| | - Chanan Angsuthanasombat
- Department of Bacterial Protein Toxin Research Cluster, Institute of Molecular Biosciences, Mahidol University, Nakornpathom 73170, Thailand; Laboratory of Molecular Biophysics and Structural Biochemistry, Biophysics Institute for Research and Development, Bangkok 10160, Thailand.
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Visitsattapongse S, Sakdee S, Leetacheewa S, Angsuthanasombat C. Single-reversal charge in the β10-β11 receptor-binding loop of Bacillus thuringiensis Cry4Aa and Cry4Ba toxins reflects their different toxicity against Culex spp. larvae. Biochem Biophys Res Commun 2014; 450:948-52. [PMID: 24971536 DOI: 10.1016/j.bbrc.2014.06.090] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/14/2014] [Accepted: 06/17/2014] [Indexed: 10/25/2022]
Abstract
Bacillus thuringiensis Cry4Aa toxin was previously shown to be much more toxic to Culex mosquito-larvae than its closely related toxin - Cry4Ba, conceivably due to their sequence differences within the β10-β11 receptor-binding loop. Here, single-Ala substitutions of five residues (Pro(510), Thr(512), Tyr(513), Lys(514) and Thr(515)) within the Cry4Aa β10-β11 loop revealed that only Lys(514) corresponding to the relative position of Cry4Ba-Asp(454) is crucial for toxicity against Culex quinquefasciatus larvae. Interestingly, charge-reversal mutations at Cry4Ba-Asp(454) (D454R and D454K) revealed a marked increase in toxicity against such less-susceptible larvae. In situ binding analyses revealed that both Cry4Ba-D454R and D454K mutants exhibited a significant increase in binding to apical microvilli of Culex larval midguts, albeit at lower-binding activity when compared with Cry4Aa. Altogether, our present data suggest that a positively charged side-chain near the tip of the β10-β11 loop plays a critical role in determining target specificity of Cry4Aa against Culex spp., and hence a great increase in the Culex larval toxicity of Cry4Ba was obtained toward an opposite-charge conversion of the corresponding Asp(454).
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Affiliation(s)
- Sarinporn Visitsattapongse
- Department of Clinical Chemistry, Faculty of Medical Technology, Mahidol University, Nakornpathom 73170, Thailand; Bacterial Protein Toxin Research Unit, Institute of Molecular Biosciences, Mahidol University, Nakornpathom 73170, Thailand
| | - Somsri Sakdee
- Bacterial Protein Toxin Research Unit, Institute of Molecular Biosciences, Mahidol University, Nakornpathom 73170, Thailand
| | - Somphob Leetacheewa
- Bacterial Protein Toxin Research Unit, Institute of Molecular Biosciences, Mahidol University, Nakornpathom 73170, Thailand
| | - Chanan Angsuthanasombat
- Bacterial Protein Toxin Research Unit, Institute of Molecular Biosciences, Mahidol University, Nakornpathom 73170, Thailand; Laboratory of Molecular Biophysics and Structural Biochemistry, Biophysics Institute for Research and Development (BIRD), Bangkok 10150, Thailand.
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