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Comment published on 27 November 2015, see Toxins 2015, 7(12), 5094-5095.
Open AccessArticle

Cloning and Characterization of a Unique Cytotoxic Protein Parasporin-5 Produced by Bacillus thuringiensis A1100 Strain

1
Department of Applied Microbial Technology, Faculty of Biotechnology and Life Science, Sojo University, 4-22-1 Ikeda, Kumamoto 860-0082, Japan
2
Biotechnology and Food Research Institute, Fukuoka Industrial Technology Center, 1465-5 Aikawa-machi, Kurume, Fukuoka 839-0861, Japan
3
Department of Bioscience and Bioinfomatics, Kyushu Institute of Technology, Iizuka, Fukuoka 820-8502, Japan
4
Graduate School of Agriculture, Kyushu University, Fukuoka 812-8581, Japan
*
Author to whom correspondence should be addressed.
Toxins 2014, 6(6), 1882-1895; https://doi.org/10.3390/toxins6061882
Received: 28 April 2014 / Revised: 29 May 2014 / Accepted: 9 June 2014 / Published: 18 June 2014
(This article belongs to the Special Issue Bacillus thuringiensis Toxins)
Parasporin is the cytocidal protein present in the parasporal inclusion of the non-insecticidal Bacillus thuringiensis strains, which has no hemolytic activity but has cytocidal activities, preferentially killing cancer cells. In this study, we characterized a cytocidal protein that belongs to this category, which was designated parasporin-5 (PS5). PS5 was purified from B. thuringiensis serovar tohokuensis strain A1100 based on its cytocidal activity against human leukemic T cells (MOLT-4). The 50% effective concentration (EC50) of PS5 to MOLT-4 cells was approximately 0.075 μg/mL. PS5 was expressed as a 33.8-kDa inactive precursor protein and exhibited cytocidal activity only when degraded by protease at the C-terminal into smaller molecules of 29.8 kDa. Although PS5 showed no significant homology with other known parasporins, a Position Specific Iterative-Basic Local Alignment Search Tool (PSI-BLAST) search revealed that the protein showed slight homology to, not only some B. thuringiensis Cry toxins, but also to aerolysin-type β-pore-forming toxins (β-PFTs). The recombinant PS5 protein could be obtained as an active protein only when it was expressed in a precursor followed by processing with proteinase K. The cytotoxic activities of the protein against various mammalian cell lines were evaluated. PS5 showed strong cytocidal activity to seven of 18 mammalian cell lines tested, and low to no cytotoxicity to the others. View Full-Text
Keywords: Bacillus thuringiensis; parasporin; cry toxin; β-pore-forming toxin Bacillus thuringiensis; parasporin; cry toxin; β-pore-forming toxin
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Ekino, K.; Okumura, S.; Ishikawa, T.; Kitada, S.; Saitoh, H.; Akao, T.; Oka, T.; Nomura, Y.; Ohba, M.; Shin, T.; Mizuki, E. Cloning and Characterization of a Unique Cytotoxic Protein Parasporin-5 Produced by Bacillus thuringiensis A1100 Strain. Toxins 2014, 6, 1882-1895.

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