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Gram-negative Bacterial Protein Secretion Systems01:17

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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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A Visual Assay to Monitor T6SS-mediated Bacterial Competition
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pH sensitivity of type III secretion system tip proteins.

Aaron P Markham1, Susan E Birket, William D Picking

  • 1Department of Pharmaceutical Chemistry, University of Kansas, Lawrence, Kansas 66047, USA.

Proteins
|January 5, 2008
PubMed
Summary

Pathogenic bacteria use type III secretion systems for infection. Tip proteins like IpaD and LcrV show distinct pH-dependent stability, revealing two functional subfamilies crucial for bacterial virulence.

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Area of Science:

  • Microbiology
  • Structural Biology
  • Biochemistry

Background:

  • Pathogenic gram-negative bacteria utilize type III secretion systems (T3SS) to inject effector proteins into host cells, subverting cellular functions.
  • T3SS apparatus includes a basal body and a needle, with tip proteins regulating effector secretion.
  • Five key T3SS tip proteins studied: IpaD (Shigella flexneri), BipD (Burkholderia pseudomallei), SipD (Salmonella spp.), LcrV (Yersinia spp.), and PcrV (Pseudomonas aeruginosa).

Purpose of the Study:

  • To characterize the conformational stability of five T3SS tip proteins (IpaD, BipD, SipD, LcrV, PcrV) under varying pH and temperature conditions.
  • To understand how pH influences protein structure, particularly relevant for bacterial passage through the gastrointestinal tract and interaction with host cell membranes.
  • To identify potential correlations between structural stability and functional mechanisms of these critical virulence factors.

Main Methods:

  • Spectroscopic techniques including far-UV circular dichroism, Trp fluorescence, ANS fluorescence, and ultraviolet absorption spectroscopy were employed.
  • Optical density and right angle scattering measurements assessed protein association and dissociation.
  • Empirical phase diagrams were constructed to integrate data from multiple techniques, providing a comprehensive view of protein behavior.

Main Results:

  • Conformational stability analysis revealed two distinct subfamilies of T3SS tip proteins based on their response to pH and temperature.
  • Subfamily 1 (IpaD, BipD, SipD) exhibited conformational differences around pH 5-6, suggesting conserved function.
  • Subfamily 2 (LcrV, PcrV) showed direct correlation between conformational stability and pH, indicating shared mechanistic properties.

Conclusions:

  • The study identified two distinct stability profiles among T3SS tip proteins, highlighting conserved functional mechanisms within these groups.
  • Understanding the pH-dependent stability of these proteins is crucial for deciphering their role in bacterial pathogenesis.
  • These findings provide insights into the structural basis of type III secretion regulation and potential targets for therapeutic intervention.