Investigating the Structural Change in Protein Aqueous Solution Using Temperature-Dependent Near-Infrared...

Area of Science:

• Biophysics
• Spectroscopy
• Protein Chemistry

Background:

• Human serum albumin (HSA) is a key circulatory protein and a common model for protein structure studies.
• Understanding protein structure and denaturation is crucial in biochemistry and medicine.

Purpose of the Study:

• To investigate the structural changes of human serum albumin (HSA) in aqueous solutions using temperature-dependent near-infrared (NIR) spectroscopy.
• To analyze the protein's denaturation process and identify key structural transitions.

Main Methods:

• Temperature-dependent NIR spectroscopy was employed on HSA solutions across a 30-85°C range.
• Continuous Wavelet Transform (CWT) was applied to enhance spectral resolution and extract overlapping signals.
• Specific spectral bands corresponding to protein structures (α-helix, β-sheet, intermediate state, side chains) were analyzed.

Main Results:

• Resolution enhancement via CWT allowed extraction of distinct spectral bands.
• Increased temperature induced a loss of α-helical structure and a gain in β-sheet structure, with denaturation observed around 55°C.
• The unfolding process involves a stable intermediate state, and side chain microenvironments change significantly around 63°C.
• Spectral changes in the 8000-5600 cm⁻¹ region indicated structural alterations in water during HSA denaturation.

Conclusions:

• Temperature-induced denaturation of HSA involves a transition from α-helix to β-sheet structures.
• The unfolding pathway proceeds through a stable intermediate state.
• NIR spectroscopy combined with CWT provides a sensitive method for monitoring protein structural dynamics and water-protein interactions during denaturation.