Related Experiment Video
Updated: Aug 4, 2026
09:42
Using SecM Arrest Sequence as a Tool to Isolate Ribosome Bound Polypeptides
Published on: June 19, 2012
SecD and SecF facilitate protein export in Escherichia coli
1Department of Microbiology and Molecular Genetics, Harvard Medical School, Boston, MA 02115.
The EMBO Journal
|February 1, 1994
Summary
The SecD and SecF proteins regulate protein translocation rates in Escherichia coli. Modulating their levels impacts protein export, with null mutants showing severe defects, highlighting their crucial role.
Area of Science:
- Molecular Biology
- Bacterial Physiology
- Protein Transport
Background:
- Protein translocation is essential for bacterial viability.
- The roles of SecD and SecF in protein export are not fully understood.
- In vitro studies suggest SecD and SecF are not essential for translocation.
Purpose of the Study:
- To investigate the role of SecD and SecF proteins in Escherichia coli protein translocation.
- To determine the impact of SecD and SecF levels on protein export efficiency.
- To reconcile conflicting data from genetic and in vitro translocation studies.
Main Methods:
- Gene overexpression and depletion in Escherichia coli.
- Construction and analysis of null mutants (secDF::kan, secD, secF).
- Assessment of protein translocation and export rates under various conditions.
Main Results:
- Overexpression of SecD and SecF enhances protein translocation and export of mutant proteins.
- Depletion of SecD and SecF significantly reduces but does not abolish translocation.
- Null mutants (secD, secF, secDF) exhibit cold sensitivity and severe export defects.
Conclusions:
- SecD and SecF are critical for efficient protein translocation in Escherichia coli.
- These proteins function together to stimulate export, distinct from other Sec factors.
- The findings support a cold-sensitive early step in protein export.
Related Concept Videos
01:20Cotranslational 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...
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...
01:26Insertion of Single-pass Transmembrane Proteins in the RER
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.
Integral transmembrane proteins possess transmembrane and extra membrane domains. The transmembrane domains are primarily made of 20-25 hydrophobic amino acids arranged in a helical secondary confirmation. These...
Integral transmembrane proteins possess transmembrane and extra membrane domains. The transmembrane domains are primarily made of 20-25 hydrophobic amino acids arranged in a helical secondary confirmation. These...
01:27Post-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...
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...
01:32Export of Misfolded Proteins out of the ER
After folding, the ER assesses the quality of secretory and membrane proteins. The correctly folded proteins are cleared by the calnexin cycle for transport to their final destination, while misfolded proteins are held back in the ER lumen. The ER chaperones attempt to unfold and refold the misfolded proteins but sometimes fail to achieve the correct native conformation. Such terminally misfolded proteins are then exported to the cytosol by ER-associated degradation or ERAD pathway for...
01:28Protein 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.
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.
01:26Bacterial 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...