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The machinery of membrane protein assembly
Stephen H White1, Gunnar von Heijne
1Department of Physiology and Biophysics, Program in Macromolecular Structure, University of California at Irvine, Irvine, California 92697-4560, USA. blanco@helium.biomol.uci.edu
Current Opinion in Structural Biology
|August 18, 2004
Summary
New insights into protein-conducting channels (translocons) reveal how they insert proteins into membranes. Structural and biophysical studies suggest protein folding begins in the ribosome before entering the translocon.
Area of Science:
- Molecular biology
- Structural biology
- Biophysics
Background:
- SecY (bacteria) and Sec61 (eukaryotes) translocons are protein-conducting channels essential for membrane protein assembly.
- These complexes work with ribosomes to insert proteins into cellular membranes.
Purpose of the Study:
- To elucidate the mechanism of translocon function using structural and biophysical approaches.
- To understand how translocons establish membrane protein topology, including the positive-inside rule.
Main Methods:
- X-ray crystallography of an archaeal SecY translocon.
- Cryo-electron microscopy and biophysical studies.
Main Results:
- The crystallographic structure of the archaeal SecY translocon offers new mechanistic insights.
- The structure provides a potential explanation for the positive-inside rule in membrane protein topology.
- Evidence suggests membrane protein folding initiates within the ribosome exit tunnel prior to translocon entry.
Conclusions:
- The structure of the SecY translocon significantly advances our understanding of its function in membrane protein insertion.
- Translocon structure and function are intimately linked to the early stages of protein folding and membrane insertion.
- The findings provide a framework for understanding how nascent proteins achieve correct topology within membranes.