Conformational transitions in phosvitin with pH variation. Vibrational circular dichroism study

Area of Science:

• Biochemistry
• Spectroscopy
• Protein Chemistry

Background:

• Phosvitin, a phosphoprotein, plays a role in metal binding and nutrient transport.
• Understanding protein structural changes at varying pH is crucial for biological function.
• Vibrational circular dichroism (VCD) is a sensitive technique for probing protein secondary structure.

Purpose of the Study:

• To investigate the pH-dependent structural transitions of metal-free phosvitin.
• To characterize the secondary structure changes using VCD and infrared (IR) spectroscopy.
• To compare the behavior of metal-free phosvitin with metal-containing preparations.

Main Methods:

• Measurement of VCD and IR spectra of metal-free phosvitin across a range of pH values.
• Qualitative analysis of spectral changes.
• Factor analysis of VCD spectra, referenced to a protein data set.
• Fourier deconvolution of solution phase absorption bands.

Main Results:

• A distinct coil-to-sheet transition was observed in metal-free phosvitin as pH decreased below 3.
• Metal-containing phosvitin showed a more gradual transition at different pH values.
• VCD identified two distinct beta-sheet forms during the low pH transition, potentially due to sheet twisting or aggregation.
• These distinct beta-sheet forms were not discernible using IR spectroscopy alone.

Conclusions:

• Metal-free phosvitin undergoes a sharp coil-to-sheet transition at low pH.
• The transition involves at least two distinct beta-sheet conformations.
• VCD spectroscopy provides higher resolution for detecting subtle structural changes compared to IR spectroscopy.
• Metal ions can influence the pH-induced structural transition of phosvitin.