Mutagenesis Targeting the S<sup>153</sup> Residue Within the Transmembrane β-Hairpin of Mosquito-Larvicidal Mpp46Ab Affects Its Toxicity and the Synergistic Toxicity with Cry4Aa
We constructed a library of Mpp46Ab mutants, in which S<sup>153</sup> within the transmembrane β-hairpin was randomly replaced by other amino acids. Mutagenesis and subsequent primary screening yielded 10 different Mpp46Ab mutants in addition to the wild type. Remarkably, S<sup>153...
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| author | Tohru Hayakawa Syun Yamaoka Mami Asakura Minako Hirano Toru Ide |
| author_facet | Tohru Hayakawa Syun Yamaoka Mami Asakura Minako Hirano Toru Ide |
| author_sort | Tohru Hayakawa |
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| description | We constructed a library of Mpp46Ab mutants, in which S<sup>153</sup> within the transmembrane β-hairpin was randomly replaced by other amino acids. Mutagenesis and subsequent primary screening yielded 10 different Mpp46Ab mutants in addition to the wild type. Remarkably, S<sup>153</sup> was replaced with a more hydrophobic amino acid in most of the mutants, and the S153I mutant in particular exhibited significantly increased toxicity. Electrophysiologic analysis using artificial lipid bilayers revealed that the single-channel conductance and <i>P</i><sub>K</sub>/<i>P</i><sub>Cl</sub> permeability ratio were significantly increased for S153I pores. This suggests that the formation of highly ion-permeable and highly cation-selective toxin pores increases the influx of cations and water into cells, thereby facilitating osmotic shock. In addition, the S153F, S153L, and S153I mutants exhibited significantly reduced synergistic toxicity with Cry4Aa. Electrophysiologic analysis showed that the S153F, S153L, and S153I mutants form toxin pores with a significantly reduced <i>P</i><sub>K</sub>/<i>P</i><sub>Na</sub> permeability ratio and a significantly increased <i>P</i><sub>K</sub>/<i>P</i><sub>Ca</sub> permeability ratio compared to wild-type pores. Thus, our results suggest that pore formation is central to the insecticidal activity of Mpp46Ab and that the ion permeability of toxin pores is a potential indicator correlated with both toxicity and synergistic toxicity with other toxins. |
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| spelling | doaj-art-ffb9faf9cdc941f0af84b6efca9c53fa2025-08-20T01:56:20ZengMDPI AGBiology2079-77372025-04-0114548910.3390/biology14050489Mutagenesis Targeting the S<sup>153</sup> Residue Within the Transmembrane β-Hairpin of Mosquito-Larvicidal Mpp46Ab Affects Its Toxicity and the Synergistic Toxicity with Cry4AaTohru Hayakawa0Syun Yamaoka1Mami Asakura2Minako Hirano3Toru Ide4Graduate School of Interdisciplinary Science and Engineering in Health Systems, Okayama University, 3-1-1 Tsushima-naka, Kita-ku, Okayama 700-8530, JapanGraduate School of Interdisciplinary Science and Engineering in Health Systems, Okayama University, 3-1-1 Tsushima-naka, Kita-ku, Okayama 700-8530, JapanGraduate School of Interdisciplinary Science and Engineering in Health Systems, Okayama University, 3-1-1 Tsushima-naka, Kita-ku, Okayama 700-8530, JapanGraduate School of Interdisciplinary Science and Engineering in Health Systems, Okayama University, 3-1-1 Tsushima-naka, Kita-ku, Okayama 700-8530, JapanGraduate School of Interdisciplinary Science and Engineering in Health Systems, Okayama University, 3-1-1 Tsushima-naka, Kita-ku, Okayama 700-8530, JapanWe constructed a library of Mpp46Ab mutants, in which S<sup>153</sup> within the transmembrane β-hairpin was randomly replaced by other amino acids. Mutagenesis and subsequent primary screening yielded 10 different Mpp46Ab mutants in addition to the wild type. Remarkably, S<sup>153</sup> was replaced with a more hydrophobic amino acid in most of the mutants, and the S153I mutant in particular exhibited significantly increased toxicity. Electrophysiologic analysis using artificial lipid bilayers revealed that the single-channel conductance and <i>P</i><sub>K</sub>/<i>P</i><sub>Cl</sub> permeability ratio were significantly increased for S153I pores. This suggests that the formation of highly ion-permeable and highly cation-selective toxin pores increases the influx of cations and water into cells, thereby facilitating osmotic shock. In addition, the S153F, S153L, and S153I mutants exhibited significantly reduced synergistic toxicity with Cry4Aa. Electrophysiologic analysis showed that the S153F, S153L, and S153I mutants form toxin pores with a significantly reduced <i>P</i><sub>K</sub>/<i>P</i><sub>Na</sub> permeability ratio and a significantly increased <i>P</i><sub>K</sub>/<i>P</i><sub>Ca</sub> permeability ratio compared to wild-type pores. Thus, our results suggest that pore formation is central to the insecticidal activity of Mpp46Ab and that the ion permeability of toxin pores is a potential indicator correlated with both toxicity and synergistic toxicity with other toxins.https://www.mdpi.com/2079-7737/14/5/489<i>Bacillus thuringiensis</i>mosquito-larvicidal proteinssynergistic toxicity<i>Culex pipiens</i> mosquito larvaeside-directed mutagenesiselectrophysiologic analysis |
| spellingShingle | Tohru Hayakawa Syun Yamaoka Mami Asakura Minako Hirano Toru Ide Mutagenesis Targeting the S<sup>153</sup> Residue Within the Transmembrane β-Hairpin of Mosquito-Larvicidal Mpp46Ab Affects Its Toxicity and the Synergistic Toxicity with Cry4Aa Biology <i>Bacillus thuringiensis</i> mosquito-larvicidal proteins synergistic toxicity <i>Culex pipiens</i> mosquito larvae side-directed mutagenesis electrophysiologic analysis |
| title | Mutagenesis Targeting the S<sup>153</sup> Residue Within the Transmembrane β-Hairpin of Mosquito-Larvicidal Mpp46Ab Affects Its Toxicity and the Synergistic Toxicity with Cry4Aa |
| title_full | Mutagenesis Targeting the S<sup>153</sup> Residue Within the Transmembrane β-Hairpin of Mosquito-Larvicidal Mpp46Ab Affects Its Toxicity and the Synergistic Toxicity with Cry4Aa |
| title_fullStr | Mutagenesis Targeting the S<sup>153</sup> Residue Within the Transmembrane β-Hairpin of Mosquito-Larvicidal Mpp46Ab Affects Its Toxicity and the Synergistic Toxicity with Cry4Aa |
| title_full_unstemmed | Mutagenesis Targeting the S<sup>153</sup> Residue Within the Transmembrane β-Hairpin of Mosquito-Larvicidal Mpp46Ab Affects Its Toxicity and the Synergistic Toxicity with Cry4Aa |
| title_short | Mutagenesis Targeting the S<sup>153</sup> Residue Within the Transmembrane β-Hairpin of Mosquito-Larvicidal Mpp46Ab Affects Its Toxicity and the Synergistic Toxicity with Cry4Aa |
| title_sort | mutagenesis targeting the s sup 153 sup residue within the transmembrane β hairpin of mosquito larvicidal mpp46ab affects its toxicity and the synergistic toxicity with cry4aa |
| topic | <i>Bacillus thuringiensis</i> mosquito-larvicidal proteins synergistic toxicity <i>Culex pipiens</i> mosquito larvae side-directed mutagenesis electrophysiologic analysis |
| url | https://www.mdpi.com/2079-7737/14/5/489 |
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