Bacillus thuringiensis toxin Cyt2Aa forms filamentous oligomers when exposed to lipid membranes or detergents

Šolinc, Gašper (author), Anderluh, Gregor (author), Podobnik, Marjetka (author)

The bacterium Bacillus thuringiensis (Bt) produces insecticidal proteins during the sporulation phase. These proteins are located in parasporal crystals consisting of two delta-endotoxin classes, crystal (Cry) and cytolytic (Cyt) toxins. In vitro, Cyt toxins show cytolytic activity against bacterial and a variety of insect and mammalian cells. They bind to cell membranes with unsaturated phospholipids and sphingomyelin. Although Bt and its parasporal crystals containing both Cry and Cyt toxins have been successfully used as bioinsecticides, the molecular mechanism of action of Cyt toxins is not yet fully understood. To address this, we exposed Cyt2Aa to lipid membranes and visualized membrane disruption process using cryo-electron microscopy. We observed two types of Cyt2Aa oligomers. First, Cyt2Aa forms smaller curved oligomers on the membrane surface that become linear over time, and detach when the membrane ruptures. Similar linear filamentous oligomers were also formed by Cyt2Aa in the presence of detergents without prior exposure to lipid membranes, which exhibited attenuated cytolytic activity. Furthermore, our data suggest that Cyt2Aa adopts different conformations between its monomeric and oligomeric forms. Overall, our results provide new evidence for a detergent-like mechanism of action of Cyt2Aa rather than the pore-forming model of target membrane disruption of this important class of insecticidal proteins.

• Language: English
• Keywords: Bacillus thuringiensis, parasporal crystal delta-endotoxins, Cyt toxin, Cyt2Aa, oligomers, detergent-like mechanism of action
• Work type: Article
• Typology: 1.01 - Original Scientific Article
• Organization: BF - Biotechnical Faculty
• Publication status: Published
• Publication version: Version of Record
• Year: 2023
• Number of pages: Str. 44-52
• Numbering: Vol. 674
• PID: 20.500.12556/RUL-152844
• UDC: 577
• ISSN on article: 1090-2104
• DOI: 10.1016/j.bbrc.2023.06.078
• COBISS.SI-ID: 158413827
• Publication date in RUL: 08.12.2023

Record is a part of a journal

• Title: Biochemical and biophysical research communications
• Shortened title: Biochem. biophys. res. commun.
• Publisher: Elsevier
• ISSN: 1090-2104
• COBISS.SI-ID: 18258983

Licences

• License: CC BY-NC-ND 4.0, Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International
• Link: http://creativecommons.org/licenses/by-nc-nd/4.0/
• Description: The most restrictive Creative Commons license. This only allows people to download and share the work for no commercial gain and for no other purposes.

Secondary language

• Language: Slovenian
• Keywords: biokemija, bakterije, bacili, toksini, lipidne membrane, oligomeri