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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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ATP-binding cassette or ABC transporter is the largest superfamily of integral membrane proteins. The transporters have transmembrane-binding domains (TMDs) and nucleotide-binding domains (NBDs). The TMDs are specific to their substrates, whereas the NBDs are similar to engines that complete ATP hydrolysis to complete the substrate transport. They can be full transporters consisting of two TMDs and NBDs, half transporters with one TMD and NBD, while some encoded with a single TMD or NBD are...
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The substrate specificity switch FlhB assembles onto the export gate to regulate type three secretion.

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This summary is machine-generated.

The type-three secretion system (T3SS) export gate

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Area of Science:

  • Microbiology
  • Structural Biology
  • Molecular Biology

Background:

  • Type-three secretion systems (T3SS) are essential for bacterial motility and virulence.
  • Protein transport via T3SS involves an export gate complex, including a crucial switch protein (FlhB/SctU).

Purpose of the Study:

  • To determine the high-resolution structure of the T3SS export gate complex, including the switch protein.
  • To elucidate the structural mechanism of substrate specificity switching in T3SS.

Main Methods:

  • Cryo-electron microscopy (cryo-EM) was used to obtain the structure of the export gate at 3.2 Å resolution.
  • Structure-informed mutagenesis was employed to investigate the function of key protein domains.

Main Results:

  • The cryo-EM structure reveals how the FlhB/SctU switch protein integrates into the export gate, interacting with FliPQR/SctRST.
  • An unusual loop structure within FlhB/SctU was identified, which appears critical for regulating gate function.
  • Mutagenesis studies confirmed the importance of this loop in controlling protein secretion.

Conclusions:

  • The structure provides unprecedented insight into the T3SS export gate mechanism.
  • Conformational changes involving FlhB/SctU and FliPQR/SctRST are proposed to regulate gate opening and substrate secretion.
  • This work lays the foundation for understanding T3SS regulation and developing novel antimicrobial strategies.