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Cys-scanning mutagenesis: a novel approach to structure function relationships in polytopic membrane proteins
S Frillingos1, M Sahin-Tóth, J Wu
1Howard Hughes Medical Institute, Departments of Physiology and Microbiology and Molecular Genetics, Molecular Biology Institute, University of California Los Angeles, Los Angeles, California 90024 1570.RonaldK@HHMI.UCLA.edu
Summary
Researchers studied lactose permease in E. coli using Cys-scanning mutagenesis. They identified key residues for transport and mapped conformational changes, revealing a flexible protein model for beta-galactoside and H+ symport.
Area of Science:
- Biochemistry
- Molecular Biology
- Membrane Protein Structure
Background:
- Lactose permease (LacY) in Escherichia coli is a crucial membrane transport protein.
- Understanding its mechanism is key to deciphering polytopic membrane protein function.
- Cys-scanning mutagenesis is a powerful tool for probing protein structure-function relationships.
Purpose of the Study:
- To identify essential residues for the beta-galactoside/H+ symport mechanism.
- To create a single-Cys mutant library for detailed structure-function analysis.
- To elucidate ligand-induced conformational changes and helix dynamics.
Main Methods:
- Cysteine scanning mutagenesis of the entire lactose permease.
- Site-directed chemical modification and reactivity assays.
- Analysis of helix packing, tilt, and ligand-induced conformational changes.
Main Results:
- Six amino acid residues were found to be indispensable for transport.
- Specific cysteine positions showed altered reactivity upon ligand binding, indicating conformational changes.
- The lactose permease was characterized as a highly flexible molecule.
Conclusions:
- A working model for the coupling of beta-galactoside and H+ translocation was developed.
- Structure-function relationships in this polytopic membrane protein were significantly advanced.
- The study provides insights into the dynamic nature of membrane transport proteins.