Small molecule perimeter defense in entomopathogenic bacteria
Jason M Crawford1, Cyril Portmann, Xu Zhang
1Department of Biological Chemistry and Molecular Pharmacology, Harvard Medical School, Boston, MA 02115, USA.
Summary
Rhabduscin, produced by insect pathogens, inhibits phenoloxidase, a key insect immune enzyme. This molecule localizes to the bacterial cell surface, suggesting a strategy for combating host defenses.
Area of Science:
- Microbiology
- Biochemistry
- Immunology
Background:
- Insect pathogens Xenorhabdus nematophila and Photorhabdus luminescens produce rhabduscin.
- Rhabduscin is a tyrosine derivative with unique functional groups.
- Phenoloxidase is a critical enzyme in the insect innate immune system responsible for melanin production.
Purpose of the Study:
- To elucidate the function and localization of rhabduscin.
- To investigate rhabduscin's role as an inhibitor of insect phenoloxidase.
- To explore the potential of bacterial cell-surface molecules as immunosuppressants.
Main Methods:
- Heterologous expression of the rhabduscin pathway in Escherichia coli.
- Precursor-directed biosynthesis of rhabduscin analogs.
- Biochemical assays and stimulated Raman scattering (SRS) and confocal fluorescence microscopy.
Main Results:
- Rhabduscin was confirmed as a potent nanomolar inhibitor of phenoloxidase.
- Rhabduscin was localized to the bacterial cell surface in both native and heterologous systems.
- Rhabduscin was essential and sufficient for phenoloxidase inhibition.
Conclusions:
- Rhabduscin's cell-surface localization facilitates effective inhibition of insect phenoloxidase at the site of contact.
- Bacterial cell-coated immunosuppressants represent a potential strategy to overcome host immune defenses.
- The rhabduscin pathway's aglycone is also found in the human pathogen Vibrio cholerae.
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