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Gallocin A, an Atypical Two-Peptide Bacteriocin with Intramolecular Disulfide Bonds Required for Activity.
Alexis Proutière1, Laurence du Merle1, Marta Garcia-Lopez1
1Institut Pasteur, Université Paris Cité, CNRS UMR6047, Biology of Gram-Positive Pathogens Unit, Paris, France.
Microbiology Spectrum
|March 23, 2023
Summary
Streptococcus gallolyticus subsp. gallolyticus (SGG) uses a two-peptide bacteriocin, gallocin A, to kill related bacteria by permeabilizing membranes. An immunity peptide, GIP, likely prevents self-intoxication by blocking gallocin A activity.
Area of Science:
- Microbiology
- Molecular Biology
- Structural Biology
Background:
- Streptococcus gallolyticus subsp. gallolyticus (SGG) is an opportunistic pathogen linked to colorectal cancer.
- SGG thrives in tumor conditions, outcompeting commensal gut bacteria.
- Gallocin A is a bacteriocin produced by SGG that enhances its colonization.
Purpose of the Study:
- To characterize the mechanism of action and resistance of gallocin A.
- To elucidate the structure and function of gallocin A's components.
- To identify potential new subclasses of bacteriocins.
Main Methods:
- Genetic analysis to identify gallocin A's peptide components (GllA1, GllA2) and immunity factor (GIP).
- Membrane permeabilization assays using lipid bilayer vesicles.
- Structural modeling and experimental confirmation of peptide structures and disulfide bonds.
- Functional assays involving gene deletions and disulfide-reducing agents.
Main Results:
- Gallocin A requires both GllA1 and GllA2 peptides for antimicrobial activity.
- Gallocin A permeabilizes bacterial membranes, killing related bacteria like Enterococcus faecalis.
- The GIP immunity peptide shares structural similarity with GllA1/GllA2, suggesting a competitive inhibition mechanism.
- Disulfide bonds are crucial for gallocin A's structure and activity.
Conclusions:
- Gallocin A is a novel two-peptide bacteriocin requiring disulfide bonds for activity.
- The GIP immunity protein likely protects SGG from self-intoxication.
- Gallocin A represents a potential new subclass of class IIb bacteriocins.
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