Abstract
Cry proteins produced by Bacillus thuringiensis are pore-forming toxins that disrupt the membrane integrity of insect midgut cells. The structure of such pore is unknown, but it has been shown that domain I is responsible for oligomerization, membrane insertion and pore formation activity. Specifically, it was proposed that some N-terminal α-helices are lost, leading to conformational changes that trigger oligomerization. We designed a series of mutants to further analyze the molecular rearrangements at the N-terminal region of Cry1Ab toxin that lead to oligomer assembly. For this purpose, we introduced Cys residues at specific positions within α-helices of domain I for their specific labeling with extrinsic fluorophores to perform Föster resonance energy transfer analysis to fluorescent labeled Lys residues located in Domains II–III, or for disulfide bridges formation to restrict mobility of conformational changes. Our data support that helix α-1 of domain I is cleaved out and swings away from the toxin core upon binding with Manduca sexta brush border membrane vesicles. That movement of helix α-2b is also required for the conformational changes involved in oligomerization. These observations are consistent with a model proposing that helices α-2b and α-3 form an extended helix α-3 necessary for oligomer assembly of Cry toxins.
Highlights
Pore-forming toxins (PFTs) are proteins produced by several pathogenic bacteria to disrupt the membrane integrity of their target cells, playing an important role in their virulence to invade or colonize their hosts
The PFTs are classified in β- or α-PFT according to the secondary structure that is inserted into the membrane
All three-dimensional structures resolved from monomeric Cry toxins contain seven α-helices, where the helix α-2 is bended, forming two small helices named α-2a and α-2b, which are connected by a flexible loop with helix α-3 (Figure 1A)
Summary
Pore-forming toxins (PFTs) are proteins produced by several pathogenic bacteria to disrupt the membrane integrity of their target cells, playing an important role in their virulence to invade or colonize their hosts. Bacillus thuringiensis (Bt) bacteria produce different PFTs highly lethal for invertebrates, mainly insects. Different Bt strains secrete Vip toxins, and in synchrony with the sporulation phase synthetize Cyt and Cry toxins, accumulating them as parasporal crystals [6,7]. All of these toxins are PFTs, and some of them are used worldwide to control insect pests in agriculture or mosquitoes that transmit infectious diseases to humans. Among the Bt toxins described so far, Cry toxins are most abundant, and at least three different non-phylogenetically related Cry families have been found, such as the three-domain Cry toxins (named Cry), the Cry Bin-like ( named Tpp and Gpp) and the Cry Mtx-like toxins ( named Mpp and Mtx) [6,7,8]
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
