Sequence-Specific Protein Secondary-Structure Assignment with Isotope Reverse-Labeled Amide I Spectroscopy

Area of Science:

• Biophysics
• Structural Biology
• Spectroscopy

Background:

• Advanced protein structure prediction tools like AlphaFold necessitate new experimental validation methods.
• Traditional atomistic methods (X-ray crystallography, NMR, CryoEM) are costly and require extensive sample preparation.
• Current spectroscopic methods (CD, FTIR) offer limited bulk secondary structure information.

Purpose of the Study:

• To develop and demonstrate a cost-effective, residue-specific protein secondary structure analysis method.
• To leverage isotope-labeled Fourier-transform infrared (FTIR) spectroscopy for enhanced structural insights.
• To complement computational protein structure predictions with experimental validation.

Main Methods:

• Developed a novel experimental approach for producing isotope-enriched FTIR spectra.
• Utilized selective 12C-labeling of individual amino acid residues in protein expression cultures.
• Applied isotope reverse-labeling and FTIR spectroscopy to the model protein Top7 V48 V.
• Analyzed isotope-labeled FTIR spectra to determine residue-specific secondary structure.

Main Results:

• Demonstrated a low-cost method for producing isotope-enriched protein samples (5 mL culture).
• Achieved residue-specific secondary structure assignments for individual amino acids.
• Obtained secondary structure assignments for amino acid stretches that align well with the known crystal structure of Top7 V48 V.
• Showcased the potential for fast and efficient sequence-specific structural information extraction.

Conclusions:

• Isotope-labeled FTIR spectroscopy offers a powerful tool for detailed protein secondary structure determination.
• This method provides a cost-effective and efficient alternative for validating protein structure predictions.
• The technique is applicable to diverse biological contexts, including live cells and membranes.