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A polytopic membrane protein displays a reversible topology dependent on membrane lipid composition
Mikhail Bogdanov1, Phillip N Heacock, William Dowhan
1Department of Biochemistry and Molecular Biology, Medical School, University of Texas-Houston, Houston, TX 77225, USA.
The EMBO Journal
|May 1, 2002
Summary
Phospholipids, like phosphatidylethanolamine (PE), are crucial for membrane protein function. Lack of PE causes lactose permease (LacY) to misfold, but adding PE can reverse this, showing topology is adaptable.
Area of Science:
- Membrane biology
- Protein biochemistry
- Microbial genetics
Background:
- Phospholipids are essential components of cell membranes, influencing protein structure and function.
- Polytopic membrane proteins, like lactose permease (LacY), span the membrane multiple times and their correct folding is critical for activity.
- Phosphatidylethanolamine (PE) is a major bacterial phospholipid, but its specific role in membrane protein topology remains incompletely understood.
Purpose of the Study:
- To investigate the role of phosphatidylethanolamine (PE) in the assembly, conformation, and function of the polytopic membrane protein lactose permease (LacY).
- To determine if membrane protein topology is fixed or can be altered by changes in phospholipid composition.
Main Methods:
- Utilized mutant strains of Escherichia coli lacking phosphatidylethanolamine (PE).
- Studied the functional activity and topological organization of lactose permease (LacY) in these mutants.
- Induced post-assembly synthesis of PE to observe its effect on LacY conformation and topology.
Main Results:
- Escherichia coli mutants lacking PE exhibited improper conformation and assembly of LacY, leading to loss of active transport function.
- In PE-lacking cells, the N-terminal half of LacY adopted an inverted topology.
- Post-assembly synthesis of PE induced a conformational change in LacY, restoring normal topology and active transport function.
Conclusions:
- Phosphatidylethanolamine is essential for the correct conformation, topology, and function of lactose permease.
- Membrane protein topology is not immutable and can be reversibly altered by changes in the cellular phospholipid composition.
- The cell may possess a post-assembly proofreading mechanism to correct misfolded membrane proteins based on lipid environment.