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The "trigger factor cycle" includes ribosomes, presecretory proteins, and the plasma membrane
1Molecular Biology Institute, University of California, Los Angeles 90024-1570.
Cell
|September 23, 1988
Summary
E. coli trigger factor (TF) protein stabilizes outer-membrane protein precursors for membrane assembly. TF cycles between ribosomes, presecretory proteins, and membrane sites, facilitating protein translocation.
Area of Science:
- Molecular Biology
- Protein Folding
- Bacterial Physiology
Background:
- Outer-membrane proteins are crucial for bacterial cell structure and function.
- The precursor form of OmpA (proOmpA) requires specific factors for proper membrane insertion.
- Ribosomes synthesize proteins, and nascent chains interact with various cellular factors.
Purpose of the Study:
- To investigate the role of trigger factor in the assembly of outer-membrane proteins.
- To characterize the interaction of trigger factor with ribosomes and presecretory proteins.
- To elucidate the mechanism of trigger factor's involvement in protein translocation.
Main Methods:
- Biochemical assays to study protein-protein interactions.
- Salt extraction and reassociation experiments to analyze trigger factor-ribosome binding.
- Competition assays to assess the role of membrane sites in proOmpA translocation.
Main Results:
- Trigger factor (TF) is a 63 kDa protein that stabilizes proOmpA for membrane assembly.
- TF binds to the 50S ribosomal subunit, where nascent polypeptide chains exit.
- Excess TF competes for membrane sites essential for proOmpA translocation.
Conclusions:
- Trigger factor acts as a chaperone, facilitating the proper folding and membrane insertion of bacterial outer-membrane proteins.
- TF exhibits a dynamic cycling mechanism, interacting with ribosomes, presecretory proteins, and membrane components.
- This cycling is critical for efficient protein translocation across the bacterial membrane.
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