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Helical packing of needles from functionally altered Shigella type III secretion systems
Frank S Cordes1, Sarah Daniell, Roma Kenjale
1Laboratory of Molecular Biophysics, University of Oxford, Oxford OX1 3QU, UK.
Journal of Molecular Biology
|October 26, 2005
Summary
Type III secretion systems (TTSS) in bacteria use a needle structure to inject proteins into host cells. Contrary to previous hypotheses, helical changes in the needle do not appear to signal host cell contact.
Area of Science:
- Microbiology
- Molecular Biology
- Cell Biology
Background:
- Gram-negative bacteria utilize Type III secretion systems (TTSS) for host-pathogen interactions.
- The TTSS extracellular needle structure is crucial for protein translocation upon host cell contact.
- Previous work suggested MxiH monomer helical packing changes signal host contact, analogous to flagella.
Purpose of the Study:
- To investigate the role of MxiH helical packing in TTSS-mediated host cell contact sensing.
- To determine if alterations in TTSS secretion states correlate with changes in needle helical structure.
Main Methods:
- Analysis of MxiH mutations affecting TTSS secretion.
- Microscopic examination of TTSS needle helical packing.
- Comparison of helical parameters between wild-type and mutant TTSS needles.
Main Results:
- Mutations altering TTSS secretion states did not result in detectable changes in needle helical packing.
- The helical parameters of TTSS needles remained consistent across different secretion states.
- Observed helical packing was similar to that of bacterial flagella.
Conclusions:
- Host cell contact signaling via TTSS may involve helical changes too subtle for current detection methods.
- Alternatively, TTSS signal transduction may operate through an uncharacterized molecular mechanism.
- The proposed analogy between TTSS needle helical packing and flagellar states for host contact sensing is not supported by these findings.
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