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The Cytoplasm-Entry Domain of Antibacterial CdiA Is a Dynamic α-Helical Bundle with Disulfide-Dependent Structural
Nicholas L Bartelli1, Sheng Sun1, Grant C Gucinski2
1Department of Chemistry and Biochemistry, University of California, Santa Barbara, CA 93106, United States.
Journal of Molecular Biology
|June 11, 2019
Summary
Contact-dependent growth inhibition (CDI) systems use toxic CdiA-CT effectors for bacterial competition. The entry domain
Area of Science:
- Microbiology
- Structural Biology
- Biochemistry
Background:
- Gram-negative bacteria utilize contact-dependent growth inhibition (CDI) systems for inter-bacterial competition.
- CDI systems involve cell-surface CdiA effectors delivering toxic C-terminal domains (CdiA-CT) into target cells.
- CdiA-CT comprises a nuclease domain and a cytoplasm-entry domain essential for toxin translocation.
Purpose of the Study:
- To investigate the structure, stability, and dynamics of the cytoplasm-entry domain of CdiA-CT from Escherichia coli STEC_MHI813.
- To elucidate the role of disulfide linkages in the structure and function of the entry domain.
Main Methods:
- Nuclear Magnetic Resonance (NMR) spectroscopy.
- Circular dichroism (CD) spectroscopy.
- Site-directed mutagenesis and chemical reduction.
Main Results:
- The CdiA-CT entry domain features a C-terminal helical bundle and a dynamic N-terminal region with two disulfide bonds.
- Disruption of disulfide bonds destabilizes the N-terminus but minimally impacts global thermodynamic stability, indicating a molten globule state.
- Disulfide bonds form in vivo in the periplasm and are crucial for the growth inhibition activity of the CDI system.
Conclusions:
- The dynamic, molten globule-like structure of the CdiA-CT entry domain is critical for its function.
- This structural flexibility allows the toxin to resist degradation while enabling membrane translocation into target cells.
- Disulfide bonds are essential for maintaining the structural integrity required for CdiA-CT mediated growth inhibition.
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