Transmission electron microscopy studies on pig gastric mucin and its interactions with chitosan

Transmission electron microscopy has been employed to visualize the molecular structure and organization of a highly purified preparation of pig gastric mucin (molar mass M~9 × 10⁶g/mol, as determined by low speed sedimentation equilibrium), prepared for microscopy by two completely independent methods. Samples were prepared for imaging by air drying on mica (in the presence of 50% glycerol) as well as critical point drying in acetone/CO₂. The data appear consistent with the accepted linear model for mucins, and are consistent with regions of variable degrees of glycosylation along the polypeptide backbone chain, with the overall conformation that of a loose or random coil. The behaviour of this mucin in a dilute solution mixture with the potential mucoadhesive polymer chitosan (M~1 60,000 g/mol) was then explored, and a clear interaction was demonstrated, consistent with dilute solution measurements using sedimentation velocity analysis in the analytical ultracentrifuge.