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Updated: May 11, 2026
Production of Disulfide-stabilized Transmembrane Peptide Complexes for Structural Studies
Published on: March 6, 2013
Production of the cannibalism toxin SDP is a multistep process that requires SdpA and SdpB
Tiara G Pérez Morales1, Theresa D Ho, Wei-Ting Liu
1Department of Microbiology, University of Iowa, Iowa City, IA, USA.
Abstract:
During the early stages of sporulation, a subpopulation of Bacillus subtilis cells secrete toxins that kill their genetically identical siblings in a process termed cannibalism. One of these toxins is encoded by the sdpC gene of the sdpABC operon. The active form of the SDP toxin is a 42-amino-acid peptide with a disulfide bond which is processed from an internal fragment of pro-SdpC. The factors required for the processing of pro-SdpC into mature SDP are not known. We provide evidence that pro-SdpC is secreted via the general secretory pathway and that signal peptide cleavage is a required step in the production of SDP. We also demonstrate that SdpAB are essential to produce mature SDP, which has toxin activity. Our data indicate that SdpAB are not required for secretion, translation, or stability of SdpC. Thus, SdpAB may participate in a posttranslation step in the production of SDP. The mature form of the SDP toxin contains a disulfide bond. Our data indicate that while the disulfide bond does increase activity of SDP, it is not essential for SDP activity. We demonstrate that the disulfide bond is formed independently of SdpAB. Taken together, our data suggest that SDP production is a multistep process and that SdpAB are required for SDP production likely by controlling, directly or indirectly, cleavage of SDP from the pro-SdpC precursor.
Insights
Bacillus subtilis cells use cannibalism to survive. The SdpAB proteins are essential for producing the mature SdpC toxin, likely by cleaving it from its precursor.
Area of Science:
- Microbiology
- Molecular Biology
- Bacterial Genetics
Background:
- Bacillus subtilis undergoes sporulation, a process involving cell death via cannibalism.
- A toxin, SDP, is produced by a subpopulation of cells to eliminate siblings.
- The sdpC gene encodes the precursor to the active SDP toxin, but processing factors are unknown.
Purpose of the Study:
- To investigate the factors and mechanisms involved in the post-translational processing of the Bacillus subtilis SDP toxin.
- To elucidate the role of SdpAB proteins in the production of mature, active SDP.
Main Methods:
- Investigated pro-SdpC secretion via the general secretory pathway.
- Assessed the necessity of signal peptide cleavage for SDP production.
- Determined the role of SdpAB in SDP maturation, secretion, translation, and stability.
- Analyzed the contribution of the disulfide bond to SDP activity and its formation.
Main Results:
- Pro-SdpC is secreted through the general secretory pathway, requiring signal peptide cleavage.
- SdpAB proteins are essential for producing mature, active SDP, but not for SdpC secretion, translation, or stability.
- SdpAB likely act in a post-translational step, possibly by mediating cleavage of SDP from pro-SdpC.
- The disulfide bond in mature SDP enhances activity but is not essential and forms independently of SdpAB.
Conclusions:
- SDP toxin production is a complex, multi-step process.
- SdpAB proteins are crucial for SDP maturation, likely by facilitating the cleavage of the active toxin from its precursor.
- Signal peptide cleavage and SdpAB-mediated processing are key steps in generating active SDP.
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