Interfacial Charge-Driven Compression-Induced Structural and Morphological Reorganization in Lysozyme-DMPA Mixed...

Area of Science:

• Biophysics
• Materials Science
• Surface Chemistry

Background:

• Protein-lipid interactions are fundamental to biological membrane structure and function.
• Understanding these interactions in simplified systems aids in deciphering complex membrane behavior.

Purpose of the Study:

• To investigate the influence of interfacial charge on the structural organization and mechanical properties of mixed lysozyme-DMPA Langmuir films.
• To explore the effects of varying lysozyme-to-DMPA ratios and subphase pH on film morphology and phase behavior.

Main Methods:

• Fabrication of mixed Langmuir films at the air-water interface using a cospreading approach.
• Characterization using surface pressure-area isotherms, compressibility modulus analysis, Brewster angle microscopy (BAM), atomic force microscopy (AFM), and X-ray reflectivity (XRR).

Main Results:

• Mixed films exhibit pressure-induced reorganization, including lateral phase separation into domains and partial vertical stratification.
• The extent of reorganization is dependent on the lysozyme-to-DMPA ratio and subphase pH.
• X-ray reflectivity and AFM reveal a layered structure with potential redistribution and lateral demixing in the upper layer.

Conclusions:

• Effective interfacial charge is a critical factor controlling the structural organization and macroscopic behavior of protein-lipid mixed Langmuir films.
• The observed structural changes upon compression are reversible, highlighting the dynamic nature of these interfaces.