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Related Concept Videos

Bacterial Translocation and Protein Secretion01:26

Bacterial Translocation and Protein Secretion

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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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Cotranslational Protein Translocation01:20

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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.
Sec61 channel partners for cotranslational translocation
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A sizable fraction of proteins destined for ER are first synthesized in the cell cytosol and then transported across the ER membrane–a process called post-translational translocation. Similar to cotranslationally translocated proteins, these proteins also use the Sec translocon complex to enter the ER lumen.
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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 transporters are a class of ATP-driven pumps that hydrolyze ATP to move solutes across the membrane. They can be grouped into importers and exporters. While exporters are present in all domains of life, importers exist only in bacteria and some plants.
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BamA forms a translocation channel for polypeptide export across the bacterial outer membrane.

Matthew Thomas Doyle1, Harris David Bernstein1

  • 1Genetics and Biochemistry Branch, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Bethesda, MD 20892, USA.

Molecular Cell
|March 11, 2021
PubMed
Summary

The bacterial outer membrane protein BamA, essential for β-barrel assembly, also acts as a channel for exporting virulence factors. This reveals a dual role for BamA in protein transport and bacterial outer membrane function.

Keywords:
BAMBamAOmp85 superfamilyautotransporterouter membrane proteinprotein foldingsecretion

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Area of Science:

  • Microbiology
  • Molecular Biology
  • Structural Biology

Background:

  • The β-barrel assembly machine (BAM) complex is crucial for integrating β-barrel proteins into the outer membrane (OM) of Gram-negative bacteria.
  • The essential BAM subunit, BamA, facilitates this process by forming a hybrid-barrel intermediate with client proteins.

Purpose of the Study:

  • To investigate potential additional functions of BamA beyond its established role in β-barrel protein integration.
  • To elucidate the mechanism by which autotransporter proteins are translocated across the OM.

Main Methods:

  • In vivo structural mapping using intermolecular disulfide crosslinking.
  • Analysis of conserved residues within autotransporter β-barrels.
  • Characterization of the hybrid-barrel state during protein translocation.

Main Results:

  • BamA functions as a polypeptide export channel, facilitating the translocation of autotransporter virulence factors across the OM.
  • The extracellular passenger domain of autotransporters traverses the OM through the BamA β-barrel lumen.
  • A conserved residue in autotransporter β-barrels is critical for initiating translocation and stabilizing the BamA hybrid-barrel intermediate.

Conclusions:

  • BamA possesses a novel function as an export channel for autotransporter proteins, in addition to its role in β-barrel assembly.
  • This finding unifies the functions of BamA and other Omp85 superfamily transporters, highlighting their broader roles in OM biogenesis and protein export.