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Related Concept Videos

Gram-negative Bacterial Protein Secretion Systems01:17

Gram-negative Bacterial Protein Secretion Systems

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Gram-negative bacteria utilize sophisticated protein secretion systems to transport proteins across their double-membrane envelope into the extracellular environment or host cells. Based on their mechanism of action, these systems are classified into one-step and two-step pathways.One-Step Secretion Systems (Types I, III, IV, and VI)One-step secretion systems bypass the periplasm entirely, forming a continuous channel that spans both the inner and outer membranes:Type I Secretion System (T1SS):...
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Fimbriae and pili are specialized bacterial surface structures that play pivotal roles in adhesion, genetic exchange, and motility. Composed primarily of pilin protein, these hairlike appendages are crucial for bacterial survival and pathogenicity in various environments.Fimbriae: Adhesion and PathogenicityFimbriae are fine, filamentous structures measuring 2–10 nanometers in diameter and are densely distributed on the bacterial cell surface. They facilitate bacterial adhesion to abiotic...
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Bacterial conjugation is a mechanism of horizontal gene transfer that enables the exchange of genetic material between bacterial cells through direct contact. This process is facilitated by a donor cell carrying a conjugative plasmid, which encodes genes necessary for pilus formation, DNA replication, and transfer. The conjugative plasmid plays a central role in initiating and executing the transfer of genetic material.The tra region of the conjugative plasmid encodes proteins responsible for...
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Bacterial protein secretion involves translocation systems to ensure proteins reach their designated locations, including the plasma membrane, periplasm, outer membrane, or the external environment. These translocation systems are vital for bacterial physiology, supporting processes like membrane assembly, enzymatic activity in the periplasm, and interactions with the external environment. The division of labor between Sec and Tat pathways ensures efficiency in handling proteins with diverse...
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Intermediate filaments (IFs) do not undergo spontaneous disassembly. Enzymes, kinases, and phosphatases add and remove phosphates from specific sites to regulate their disassembly. The IF concentration in the cytoplasm also regulates the disassembly. If the concentration crosses a threshold, it activates the protein kinases in the vicinity, allowing the phosphorylation of IFs.
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Integrative structural analysis of the type III secretion system needle complex from Shigella flexneri.

Lara Flacht1,2, Michele Lunelli1, Karol Kaszuba1,3

  • 1Department for Structural Infection Biology, Center for Structural Systems Biology (CSSB) & Helmholtz Centre for Infection Research (HZI), Hamburg, Germany.

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Summary

The structure of the type III secretion system (T3SS) in Shigella flexneri reveals unique features and conserved elements. This detailed analysis of the T3SS needle complex advances understanding for potential broad-range therapeutics.

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Area of Science:

  • Microbiology
  • Structural Biology
  • Bacterial Pathogenesis

Background:

  • The type III secretion system (T3SS) is a critical virulence factor for pathogenic Gram-negative bacteria.
  • Understanding T3SS structure is key for developing targeted therapeutics.
  • Limited structural data exists for T3SSs beyond Salmonella, hindering cross-species comparisons.

Purpose of the Study:

  • To determine the high-resolution structure of the T3SS needle complex from Shigella flexneri.
  • To identify conserved and unique structural features of the Shigella T3SS compared to other species.
  • To provide insights for the development of novel anti-virulence strategies.

Main Methods:

  • Cryo-electron microscopy (cryo-EM) for high-resolution imaging.
  • Cross-linking mass spectrometry (XL-MS) to map protein-protein interactions.
  • Integrative modeling to assemble the complete T3SS needle complex structure.

Main Results:

  • The Shigella T3SS secretin pore complex displays a novel fold in its S domain.
  • The pilotin MxiM[SctG] is localized to the outer surface of the secretin pore.
  • The export apparatus includes the N-terminal domain of SpaS[SctU], a feature not seen in prior virulence-related T3SS structures.
  • A conserved pseudohelical arrangement of the export apparatus is maintained, anchored by flexible linkers.

Conclusions:

  • The Shigella T3SS possesses unique structural characteristics differentiating it from other known T3SSs.
  • Conserved and unique features of the T3SS necessitate species-specific structural analysis.
  • The determined structure offers a foundation for designing targeted therapeutics against Shigella infections.