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Protein folding during cotranslational translocation in the endoplasmic reticulum
Michael Kowarik1, Stephanie Küng, Bruno Martoglio
1Institute of Biochemistry, Swiss Federal Institute of Technology, ETH Hönggerberg, HPM, CH-8093, Zürich, Switzerland.
Molecular Cell
|November 7, 2002
Summary
Nascent polypeptide domains must exit the translocon channel to fold. However, signal-anchored membrane proteins may experience less stringent folding constraints within the translocon complex.
Area of Science:
- Molecular Biology
- Protein Folding
- Cellular Biology
Background:
- The translocon complex facilitates protein translocation across membranes.
- Understanding the constraints on nascent polypeptide folding during translocation is crucial for protein biogenesis.
Purpose of the Study:
- To determine the minimum distance a nascent polypeptide must travel within the translocon channel before it can fold.
- To investigate if signal-anchored membrane proteins face different folding constraints.
Main Methods:
- In vitro translation of truncated mRNAs encoding the Semliki Forest virus capsid protease domain (Cp).
- Analysis of Cp folding during translocation into microsomes.
- Varying the length of the C-terminal linker to the peptidyltransferase center.
Main Results:
- Cp folding required a C-terminal linker of at least 64 amino acids, indicating it must exit the translocon channel.
- With an uncleaved signal sequence, approximately 25% of Cp domains folded with shorter linkers (38-66 amino acids).
Conclusions:
- Nascent polypeptides generally need to exit the translocon channel to fold.
- The translocon's folding constraints may be less restrictive for signal-anchored membrane proteins.