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The insecticidal toxin makes caterpillars floppy 2 (Mcf2) shows similarity to HrmA, an avirulence protein from a
Nicholas R Waterfield1, Phillip J Daborn, Andrea J Dowling
1Department of Biology and Biochemistry, University of Bath BA2 7AY, UK.
Abstract:
The Photorhabdus luminescens W14 toxin encoding gene makes caterpillars floppy (mcf) was discovered due to its ability to kill caterpillars when expressed in Escherichia coli. Here we describe a homologue of mcf (renamed as mcf1), termed mcf2, discovered in the same genome. The mcf2 gene predicts another large toxin whose central domain, like Mcf1, also shows limited homology to Clostridium cytotoxin B. However, the N-terminus of Mcf2 shows significant similarity to the type-III secreted effector HrmA from the plant pathogen Pseudomonas syringae and no similarity to the N-terminus of Mcf1. HrmA is a plant avirulence gene whose transient expression in tobacco cells results in cell death. Here we show that E. coli expressing Mcf2 can, like E. coli expressing Mcf1, kill insects. Further, expression of the c-Myc tagged N-terminus of Mcf2, the region showing similarity to HrmA, results in nuclear localisation of the fusion protein and subsequent destruction of transfected mammalian cells. The Mcf1 and Mcf2 toxins therefore belong to a family of high molecular mass toxins, differing at their N-termini, which encode different effector domains.
Insights
Photorhabdus luminescens toxins Mcf1 and Mcf2 kill insects. Mcf2
Area of Science:
- Microbiology
- Molecular Biology
- Toxicology
Background:
- Photorhabdus luminescens W14 toxin gene makes caterpillars floppy (mcf) discovered for insecticidal properties.
- A homologue, mcf2, was identified in the same bacterial genome.
Purpose of the Study:
- To characterize the newly discovered mcf2 toxin gene and its encoded protein.
- To compare the structure and function of Mcf2 with the previously identified Mcf1 toxin.
Main Methods:
- Gene cloning and expression in Escherichia coli.
- Homology analysis of Mcf2 with known bacterial and plant pathogen proteins.
- Cell-based assays in mammalian cells to assess toxicity and localization.
Main Results:
- E. coli expressing Mcf2 demonstrated insecticidal activity, similar to Mcf1.
- The N-terminus of Mcf2 shares similarity with Pseudomonas syringae HrmA, a plant avirulence factor.
- Expression of Mcf2's N-terminus in mammalian cells led to nuclear localization and cell death.
Conclusions:
- Mcf1 and Mcf2 represent a family of large toxins from Photorhabdus luminescens.
- The toxins possess distinct N-terminal domains, suggesting different effector functions.
- Mcf2's N-terminus may contribute to its toxicity through mechanisms involving nuclear localization.
