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Related Concept Videos

Protein Translocation Machinery on the ER Membrane01:28

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The translocon complex situated on the ER membrane is the main gateway for the protein secretory pathway. It facilitates the transport of nascent peptides into the ER lumen and their insertion into the ER membrane.
Sec61 protein conducting channel
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Translocation of proteins across membranes is an ancient process that occurs even in bacteria and archaebacteria. In fact, the components of the translocation machinery are still conserved between prokaryotes and eukaryotes.
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Integral membrane proteins are proteins adhered to the lipid bilayer of a cell organelle or membrane. They can be of two types: transmembrane integral proteins that span the lipid bilayer and monotopic proteins that are attached to either side of the membrane but do not pass through it.
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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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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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Related Experiment Video

Updated: Mar 26, 2026

Monitoring the Assembly of a Secreted Bacterial Virulence Factor Using Site-specific Crosslinking
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Type 3 Secretion Translocators Spontaneously Assemble a Hexadecameric Transmembrane Complex.

Fabian B Romano1, Yuzhou Tang1, Kyle C Rossi2

  • 1From the Program in Molecular and Cellular Biology, and.

The Journal of Biological Chemistry
|January 21, 2016
PubMed
Summary

Bacterial type 3 secretion system translocators PopB and PopD form unique hetero-oligomers in membranes. Their interaction guides assembly, enabling effector translocation into eukaryotic cells.

Keywords:
membrane proteinmembrane transportoligomerprotein translocationsingle-molecule biophysicstype III secretion system (T3SS)

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Area of Science:

  • Microbiology
  • Molecular Biology
  • Biophysics

Background:

  • Type 3 secretion systems (T3SS) are crucial virulence factors in bacterial pathogens.
  • T3SS translocators, like PopB and PopD from *Pseudomonas aeruginosa*, form pores in eukaryotic membranes for effector protein delivery.
  • The precise assembly and stoichiometry of these translocators within the lipid bilayer remain poorly understood.

Purpose of the Study:

  • To elucidate the oligomeric states and assembly mechanisms of *Pseudomonas aeruginosa* translocators PopB and PopD.
  • To determine the stoichiometry of hetero-complexes formed by PopB and PopD in membranes.
  • To understand how these interactions facilitate functional translocon formation for effector translocation.

Main Methods:

  • Single-molecule fluorescence photobleaching experiments were employed to analyze the oligomeric states of PopB and PopD.
  • Analysis of protein complex formation in lipid bilayers upon co-incubation of PopB and PopD.

Main Results:

  • PopD predominantly formed hexameric structures in membranes.
  • PopB exhibited a bi-modal distribution, forming hexameric and dodecameric structures.
  • Co-assembly of PopB and PopD resulted in a distinct hetero-oligomer composed of 8 PopB and 8 PopD molecules, essential for function.

Conclusions:

  • The interaction between PopB and PopD is critical for the formation of a specific hetero-oligomeric translocon.
  • This unique hetero-oligomer structure is likely key to the functional translocation of bacterial effectors into host cells.
  • Understanding this assembly process provides insights into T3SS-mediated pathogenesis.