Protein secondary structure from Fourier transform infrared spectroscopy: a data base analysis

Area of Science:

• Biophysics
• Spectroscopy
• Protein Structure Analysis

Background:

• Protein secondary structure analysis is crucial for understanding protein function.
• Circular Dichroism (CD) spectroscopy is a common method, but can be influenced by various factors.
• Fourier Transform Infrared (FTIR) spectroscopy offers an alternative approach.

Purpose of the Study:

• To develop and validate a novel infrared (IR) spectroscopy method for determining protein secondary structure in solution.
• To compare the performance of the IR method against the established CD matrix method.
• To assess the IR method's robustness and applicability.

Main Methods:

• Utilized the amide I region (1700-1600 cm-1) of FTIR spectra from 17 proteins.
• Constructed an IR data matrix from normalized spectra and a secondary structure matrix from X-ray crystallographic data.
• Employed a matrix method analogous to the CD approach by Compton and Johnson (1986).
• Compared IR and CD results by analyzing proteins from both databases as unknowns.

Main Results:

• The IR method yielded results comparable to X-ray crystallographic data, similar to the CD method.
• The IR method showed slightly better accuracy for beta-sheet structure compared to CD.
• The IR method demonstrated robustness, being less affected by aromatic groups and not requiring protein concentration or path length information.
• Extracted IR spectra for different secondary structures (helix, beta-sheet, beta-turn, other) aligned with literature assignments.

Conclusions:

• The developed IR spectroscopy method is a reliable tool for protein secondary structure determination in solution.
• This IR method provides a valuable alternative to CD spectroscopy, particularly for beta-sheet analysis.
• The IR method's independence from protein concentration and cell path length enhances its practical utility.