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Related Concept Videos

Bacterial Translocation and Protein Secretion01:26

Bacterial Translocation and Protein Secretion

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...
Cotranslational Protein Translocation01:20

Cotranslational Protein Translocation

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
During cotranslational translocation, the Sec61 channel partners with the signal recognition particle (SRP), the signal recognition particle receptor (SR), and the ribosomes to transport the nascent polypeptide chain...
Gram-negative Bacterial Protein Secretion Systems01:17

Gram-negative Bacterial Protein Secretion Systems

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):...
Formation of Lipopolysaccharides01:19

Formation of Lipopolysaccharides

Lipopolysaccharides (LPS) are crucial components of the outer membrane of Gram-negative bacteria, serving both structural and functional roles. It contributes to membrane stability and protects bacteria from host immune responses. LPS is composed of three major regions—lipid A, a core oligosaccharide, and an O antigen. The biosynthesis and assembly of LPS involve a highly coordinated set of enzymatic reactions and transport mechanisms. Additionally, LPS is recognized as an endotoxin, triggering...
Protein Translocation Machinery on the ER Membrane01:28

Protein Translocation Machinery on the ER Membrane

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
In eukaryotes, the translocon complex comprises a core heterotrimeric translocator channel called the Sec61 complex. This channel includes three transmembrane proteins, Sec61α, Sec61β, and Sec61γ, and is the largest subunit of the translocon complex.
Post-translational Translocation of Proteins to the RER01:27

Post-translational Translocation of Proteins to the RER

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.
Targeting proteins to the ER
Hsp40 and Hsp70 chaperone molecules bind the translated proteins in the cytosol to prevent their folding. The chaperone binding helps to keep the signal...

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Monitoring the Assembly of a Secreted Bacterial Virulence Factor Using Site-specific Crosslinking
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Differential localization of the streptococcal accessory sec components and implications for substrate export.

Yihfen T Yen1, Todd A Cameron, Barbara A Bensing

  • 1San Francisco Veteran Affairs Medical Center and University of California, San Francisco, CA, USA.

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The Streptococcus gordonii accessory Sec system

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Area of Science:

  • Microbiology
  • Molecular Biology
  • Protein Transport

Background:

  • The accessory Sec system in Streptococcus gordonii facilitates the export of the serine-rich glycoprotein GspB.
  • Previous studies indicated interactions between accessory Sec proteins (Asp1-5) and GspB or SecA2.

Purpose of the Study:

  • To investigate the subcellular localization of accessory Sec proteins (Asp1-3) in Streptococcus gordonii and Escherichia coli.
  • To determine how the localization of these proteins is influenced by the presence of other Sec system components.

Main Methods:

  • Fluorescence microscopy in Escherichia coli expressing the streptococcal accessory Sec system.
  • Cell fractionation studies in Streptococcus gordonii.

Main Results:

  • SecA2 localized to multiple foci at the cell membrane in E. coli.
  • Asp2 localized to cell poles alone but formed punctate membrane patterns with SecA2.
  • Asp1 and Asp3 localized diffusely in the cytosol alone or with SecA2, but redistributed to the membrane with all components present.

Conclusions:

  • Asp1-3 are not integral membrane proteins forming the translocation channel.
  • SecA2 acts as a docking site for Asp2, which recruits Asp1 and Asp3 to the membrane.
  • These interactions are crucial for GspB trafficking and translocation to the cell membrane.