Measuring proteins in H₂O with 2D-IR spectroscopy.

Area of Science:

• Biophysics
• Spectroscopy
• Biochemistry

Background:

• Protein secondary structure is sensitive to the amide I infrared band.
• Water absorption interferes with protein IR spectroscopy under physiological conditions, necessitating deuteration.
• Deuteration raises questions about protein dynamics and is impractical for applications.

Purpose of the Study:

• To demonstrate 2D-IR spectroscopy's capability to analyze proteins in water without deuteration.
• To investigate the implications of measuring protein spectroscopy and dynamics in aqueous solutions.
• To assess the clinical relevance of 2D-IR spectroscopy for serum protein analysis.

Main Methods:

• Utilized 2D-IR spectroscopy to analyze protein amide I signatures in water.
• Employed equine blood serum as a test system.
• Measured vibrational relaxation dynamics and differentiated protein fractions.

Main Results:

• 2D-IR amide I signature of proteins dominates water signals, enabling analysis in aqueous solutions.
• Deuteration was found to slow amide I vibrational relaxation by over 10%, impacting protein dynamics.
• Accurate measurement of the albumin to globulin ratio (±4%) and differentiation of IgG, IgA, and IgM were achieved.

Conclusions:

• 2D-IR spectroscopy offers a viable method for studying protein secondary structure and dynamics in water.
• This technique provides a direct spectroscopic approach for clinically relevant serum protein measurements.
• 2D-IR spectroscopy has potential applications from fundamental research to clinical diagnostics.