Heterogeneity and persistence length in human ocular mucins

Area of Science:

• Biophysics
• Materials Science
• Biochemistry

Background:

• Human ocular mucins are complex glycoproteins crucial for eye surface lubrication and protection.
• Understanding their structural heterogeneity and flexibility is key to comprehending their function in vivo.

Purpose of the Study:

• To investigate the heterogeneity and flexibility of human ocular mucins using Atomic Force Microscopy (AFM).
• To determine the equilibrium conformations of mucins adsorbed onto a surface.
• To correlate structural properties with in vivo functions.

Main Methods:

• Atomic Force Microscopy (AFM) was employed to visualize and measure mucin conformations.
• Mucins were deposited from a buffer containing Ni(2+) ions onto mica surfaces.
• The worm-like chain model was adapted for 2D analysis to confirm equilibrium adsorption.
• Native mucins were reduced with dithiothreitol to break disulfide bonds.

Main Results:

• Mucins adopted extended conformations on mica, similar to DNA under comparable conditions.
• A histogram of contour lengths demonstrated significant heterogeneity in native mucins.
• Reduction of disulfide bonds led to a marked decrease in polymer length.
• The determined persistence length of native mucin was 36 nm, indicating a flexible polymer.

Conclusions:

• AFM provides insights into the structural heterogeneity and flexibility of ocular mucins.
• The observed conformations and flexibility are consistent with mucin transport and assembly mechanisms in vivo.
• The flexible nature of mucins is a critical factor influencing the properties of ocular surface gels.