Characterization of the channel-pores formed by Bacillus thuringiensis Cry46Ab toxin in planar lipid bilayers
2019
Sakakibara, A. (Okayama University, Okayama (Japan). Graduate School of Interdisciplinary Science and Engineering in Health Systems) | Takabe, S. | Ide, T. | Hayakawa, T.
Cry46Ab from Bacillus thuringiensis TK-E6 is a new mosquitocidal toxin with aerolysin-type architecture, and has been shown that co-administration of Cry46Ab with other mosquitocidal Cry toxins results in synergistic toxicity against Culex pipiens Coquillett (Diptera: Culicidae) mosquito larvae. Cry46Ab, therefore, is expected to find use in improving the insecticidal activity of B. thuringiensis-based bioinsecticides. In the present study, the mode of action of Cry46Ab was explored by single-channel measurements of Cry46Ab channel-pores. The single-channel conductances of channel-pores formed in planar lipid bilayers by Cry46Ab were determined to be 31.8±2.7 pS in 150 mM NaCl and 24.2±0.7 pS in 150 mM CaCl2. Ion-selectivity measurements revealed that the channel-pores formed by Cry46Ab were cation selective. The permeability ratio of Ksup(+) to Clsup(-) was approximately 4, and the preferences for cations were Ksup(+) > Nasup(+), Ksup(+) > Casup(2+), and Casup(2+) > Nasup(+). A calcein release assay using liposomes suggested that Cry46Ab influences the integrity of membrane vesicles. Formation of cation-selective channel-pores has been observed with other insecticidal Cry toxins that have structures distinct from those of Cry46Ab; the capability of forming such pores may be a property required of insecticidal toxins.
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