Water-mucin phases: conditions for mucus liquid crystallinity

Previous studies of mucin conformation in aqueous media have focussed on the polymer backbone, on dilute concentrations, and on ambient temperatures. Using differential scanning calorimetry and transmitted polarised light microscopy, we demonstrate that commercially available pig gastric mucin forms a liquid crystalline gel at concentrations above approximately 26% w/w in water. Solvated mucin exhibits a glass transition at approximately 24.8 degrees C, and the liquid crystalline phase is only fluid above this temperature. We associate the glass transition with the onset of flexibility in the backbone of glycosylated molecular segments. Consideration of molecular geometry suggests that mucin liquid crystallinity is governed by interactions between side chains, not main chains. For mucin from a given source, neither the conditions required for liquid crystallinity nor the glass transition temperature should be sensitive to the mucin molecular weight, as long as the integrity of the glycosylated segments is maintained. We consider some physiological implications of our results, including the impact of hypothermic conditions on the functionality of mucus, and we emphasise the need to characterise mucin and mucus structure at physiological temperatures. (C) 1998 Elsevier Science B.V.