E. coli "Stablelabel" S30 lysate for optimized cell-free NMR sample preparation.

Area of Science:

• Biochemistry
• Molecular Biology
• Biophysics

Background:

• Cell-free (CF) protein synthesis using E. coli lysates is valuable for producing labeled proteins for NMR.
• Isotope label scrambling in CF lysates leads to ambiguous NMR signals and label dilution.
• Existing inhibitor cocktails have limitations in availability and potential side effects.

Purpose of the Study:

• To develop optimized E. coli lysates with reduced amino acid scrambling activity for CF synthesis.
• To improve the quality and reliability of isotope-labeled proteins produced via CF synthesis for NMR studies.
• To enable new labeling strategies, such as methyl group specific labeling.

Main Methods:

• Engineered E. coli strain A19 by eliminating enzymes with suspected amino acid scrambling activity.
• Created single and cumulative chromosomal mutations to reduce scrambling.
• Analyzed CF S30 lysates from mutant strains for protein synthesis efficiency and scrambling activity.
• Developed the "Stablelabel" derivative with specific mutations (asnA, ansA/B, glnA, aspC, ilvE).

Main Results:

• The "Stablelabel" E. coli derivative yielded highly effective CF S30 lysates with significantly reduced amino acid scrambling.
• CF synthesized proteins in "Stablelabel" lysates exhibited optimized NMR spectral complexity.
• Demonstrated a novel strategy for methyl group specific labeling of membrane proteins using the ilvE deletion.

Conclusions:

• Engineered E. coli lysates, like "Stablelabel", provide a superior alternative to inhibitor cocktails for minimizing label scrambling in CF protein synthesis.
• "Stablelabel" lysates enhance the utility of CF synthesis for producing precisely labeled proteins for NMR.
• The developed strategy opens new avenues for advanced protein labeling techniques, particularly for membrane proteins.