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Open AccessArticle

The C-Terminal Domain of the Bacillus thuringiensis Cry4Ba Mosquito-Specific Toxin Serves as a Potential Membrane Anchor

1
Microbial Biotechnology Unit, Department of Microbiology, Faculty of Liberal Arts and Science, Kasetsart University, Nakornpathom 73140, Thailand
2
Division of Biology, Department of Science, Faculty of Science and Technology, Prince of Songkla University, Pattani 94000, Thailand
3
Department of Pathology, Faculty of Medicine, Prince of Songkla University, Songkla 90100, Thailand
4
Bacterial Toxin Research Innovation Cluster (BRIC), Institute of Molecular Biosciences, Mahidol University, Salaya Campus, Nakornpathom 73170, Thailand
5
Laboratory of Synthetic Biophysics and Chemical Biology, Biophysics Institute for Research and Development (BIRD), Chiang Mai 50130, Thailand
*
Author to whom correspondence should be addressed.
Toxins 2019, 11(2), 62; https://doi.org/10.3390/toxins11020062
Received: 16 December 2018 / Revised: 15 January 2019 / Accepted: 18 January 2019 / Published: 23 January 2019
(This article belongs to the Special Issue Insecticidal Toxins from Bacillus thuringiensis)
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. View Full-Text
Keywords: Cry4Ba toxin; C-terminal domain; membrane anchor; pore formation; proteinase K; β-sheet structure Cry4Ba toxin; C-terminal domain; membrane anchor; pore formation; proteinase K; β-sheet structure
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MDPI and ACS Style

Thammasittirong, A.; Imtong, C.; Sriwimol, W.; Sakdee, S.; Angsuthanasombat, C. The C-Terminal Domain of the Bacillus thuringiensis Cry4Ba Mosquito-Specific Toxin Serves as a Potential Membrane Anchor. Toxins 2019, 11, 62. https://doi.org/10.3390/toxins11020062

AMA Style

Thammasittirong A, Imtong C, Sriwimol W, Sakdee S, Angsuthanasombat C. The C-Terminal Domain of the Bacillus thuringiensis Cry4Ba Mosquito-Specific Toxin Serves as a Potential Membrane Anchor. Toxins. 2019; 11(2):62. https://doi.org/10.3390/toxins11020062

Chicago/Turabian Style

Thammasittirong, Anon; Imtong, Chompounoot; Sriwimol, Wilaiwan; Sakdee, Somsri; Angsuthanasombat, Chanan. 2019. "The C-Terminal Domain of the Bacillus thuringiensis Cry4Ba Mosquito-Specific Toxin Serves as a Potential Membrane Anchor" Toxins 11, no. 2: 62. https://doi.org/10.3390/toxins11020062

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