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Structural and functional analysis of the kid toxin protein from E. coli plasmid R1
David Hargreaves1, Sandra Santos-Sierra, Rafael Giraldo
1Krebs Institute for Biomolecular Research, Department of Molecular Biology and Biotechnology, University of Sheffield, Western Bank, United Kingdom.
Insights
The Kid toxin protein, crucial for plasmid inheritance in E. coli, forms a dimer structurally similar to CcdB. Its toxicity mechanism differs from CcdB, with a distinct target interaction site proposed.
Area of Science:
- Structural Biology
- Microbiology
- Molecular Genetics
Background:
- The Kid toxin protein from E. coli plasmid R1 is essential for stable plasmid inheritance via post-segregational killing.
- Kid functions as a two-component system with its antagonist, the Kis antitoxin.
- Understanding the structure and function of Kid is vital for comprehending plasmid stability mechanisms.
Purpose of the Study:
- To determine the high-resolution crystal structure of the Kid toxin protein.
- To elucidate the structural basis of Kid's toxicity and its interaction with the Kis antitoxin.
- To compare the structural features of Kid with other related toxin proteins, such as CcdB.
Main Methods:
- X-ray crystallography was employed to determine the 1.4 Å resolution structure of the Kid toxin.
- Analysis of nontoxic Kid mutants was performed to identify key regions involved in target interaction and toxicity.
- Structural comparisons were made between Kid and the DNA gyrase-inhibitory protein CcdB.
Main Results:
- The crystal structure revealed that Kid forms a 2-fold symmetric dimer.
- Kid shares structural resemblance with the E. coli F plasmid toxin CcdB, despite lacking significant sequence similarity.
- Mutant analysis suggests a distinct target interaction interface for Kid toxicity compared to CcdB, potentially overlapping with the antitoxin binding site.
Conclusions:
- The determined structure provides insights into the dimeric state and overall fold of the Kid toxin.
- Kid's structural similarity to CcdB, coupled with differences in functional interfaces, highlights convergent evolution in toxin-antitoxin systems.
- The proposed interaction region for Kis antitoxin offers a potential explanation for the neutralization mechanism and provides a basis for future functional studies.
Abstract:
We have determined the structure of Kid toxin protein from E. coli plasmid R1 involved in stable plasmid inheritance by postsegregational killing of plasmid-less daughter cells. Kid forms a two-component system with its antagonist, Kis antitoxin. Our 1.4 A crystal structure of Kid reveals a 2-fold symmetric dimer that closely resembles the DNA gyrase-inhibitory toxin protein CcdB from E. coli F plasmid despite the lack of any notable sequence similarity. Analysis of nontoxic mutants of Kid suggests a target interaction interface associated with toxicity that is in marked contrast to that proposed for CcdB. A possible region for interaction of Kid with the antitoxin is proposed that overlaps with the target binding site and may explain the mode of antitoxin action.