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Conversion of a transmembrane to a water-soluble protein complex by a single point mutation
Yulia Tsitrin1, Craig J Morton, Catherine el-Bez
1Department of Genetics and Microbiology, University of Geneva, 1 rue Michel Servet, 1211 Geneva, Switzerland.
Nature Structural Biology
|September 10, 2002
Summary
A single point mutation in aerolysin, a pore-forming toxin, converts it from a membrane-embedded protein to a soluble complex. This Y221G mutation blocks hemolytic activity while maintaining structural integrity.
Area of Science:
- Biochemistry
- Molecular Biology
- Structural Biology
Background:
- Proteins are typically either membrane-associated or soluble.
- Pore-forming proteins are exceptions, starting soluble and becoming membrane-bound.
- Aerolysin is a pore-forming toxin that inserts into cell membranes.
Purpose of the Study:
- To investigate the structural and functional consequences of a specific mutation in aerolysin.
- To understand how mutations affect the membrane-association of pore-forming toxins.
- To determine if a single point mutation can alter the solubility of aerolysin.
Main Methods:
- Site-directed mutagenesis to create the Y221G aerolysin mutant.
- Cryo-negative staining electron microscopy (EM) for structural analysis.
- Three-dimensional reconstruction to determine complex structure.
Main Results:
- The Y221G mutation abolished hemolytic activity but preserved initial structure and receptor binding.
- The Y221G mutant formed stable heptameric complexes, similar in overall structure to wild-type aerolysin.
- Unlike the hydrophobic wild-type heptamer, the Y221G heptamer was fully hydrophilic, indicating a soluble complex.
Conclusions:
- A single point mutation (Y221G) can convert a membrane-embedded toxin into a soluble complex.
- This mutation highlights the delicate balance between protein structure and membrane association.
- The findings offer insights into the mechanisms of protein localization and function.