A genetically encoded spin label for electron paramagnetic resonance distance measurements

Area of Science:

• Biochemistry
• Molecular Biology
• Biophysics

Background:

• Electron paramagnetic resonance (EPR) spectroscopy is a powerful technique for studying protein dynamics and structure.
• Traditional EPR studies require chemical labeling of proteins, which can be complex and may alter protein function.
• There is a need for methods that allow direct, site-specific labeling of proteins within living cells.

Purpose of the Study:

• To genetically encode a novel, spin-labeled amino acid in Escherichia coli (E. coli).
• To enable the intracellular biosynthesis of spin-labeled proteins, eliminating the need for chemical labeling.
• To explore the utility of this method for in-cell EPR studies and intramolecular distance measurements.

Main Methods:

• Genetic encoding of a noncanonical amino acid in E. coli.
• Site-directed mutagenesis to introduce the amino acid at specific protein locations.
• Culturing engineered E. coli for protein expression.
• Double-electron electron resonance (DEER) measurements for distance determination.
• Selective detection of spin-labeled proteins within cells.

Main Results:

• Successful genetic encoding and stable expression of the spin-labeled amino acid in E. coli.
• Demonstrated ability to introduce the amino acid at multiple, user-defined sites in proteins.
• Confirmed stability of the labeled protein during prolonged expression.
• Utilized double-electron electron resonance (DEER) to measure intramolecular distances.
• Achieved selective detection of spin-labeled proteins within intact E. coli cells.

Conclusions:

• Genetic encoding of spin-labeled amino acids offers a streamlined approach for producing labeled proteins.
• This method bypasses the limitations of traditional chemical labeling techniques.
• The developed system opens new avenues for in-cell EPR spectroscopy of endogenous proteins, providing insights into biological processes in their native environment.