Photoactive Yellow Protein Adsorption at Hydrated Polyethyleneimine and Poly-l-Glutamic Acid Interfaces

Area of Science:

• Biophysics
• Spectroscopy
• Surface Science

Background:

• Photoactive yellow protein (PYP) is a model system for studying protein structure and function.
• Understanding protein adsorption at interfaces is crucial for biomaterial design and biosensor development.
• Polyelectrolyte multilayers offer tunable surfaces for controlling protein adsorption.

Purpose of the Study:

• To investigate the interfacial structure of photoactive yellow protein (PYP) adsorbed on polyelectrolyte surfaces using chiral and achiral vibrational sum-frequency generation (VSFG) spectroscopy.
• To determine the sensitivity of VSFG spectroscopy to protein secondary and tertiary structures at interfaces.
• To explore the influence of substrate properties and environmental conditions (humidity) on protein adsorption and conformation.

Main Methods:

• Vibrational sum-frequency generation (VSFG) spectroscopy (chiral and achiral) in the 1400-1700 cm⁻¹ and 2800-3800 cm⁻¹ ranges.
• Adsorption of PYP onto nanometer-thick polyelectrolyte layers (polyethyleneimine and poly-l-glutamic acid).
• Systematic variation of polyelectrolyte layer composition and ambient humidity.

Main Results:

• Homogeneous PYP adsorption was achieved on 6.5-pair polyelectrolyte layers.
• VSFG spectra indicated increased PYP adsorption on poly-l-glutamic acid (PGA) compared to polyethyleneimine (PEI) surfaces.
• Changes in VSFG spectra revealed sensitivity to PYP's secondary structure (β-scaffold) and tertiary structure, including α-helix re-orientation under decreasing humidity.

Conclusions:

• Chiral VSFG spectroscopy is a powerful tool for characterizing protein secondary and tertiary structures at interfaces.
• The study demonstrates the ability of VSFG to detect conformational changes in PYP due to substrate interactions and humidity.
• Polyelectrolyte surfaces can be tailored to influence protein adsorption and structure.