Study of mucin interaction with model phospholipid membrane at the air-water interface

The aim of the present study was to determine the interfacial behavior of model biomembrane in the presence of mucin. The Langmuir monolayer technique was used to form a mixed protein-phospholipid film at the air-water interface. Using the surface pressure-area isotherms, the relaxation curves and adsorption experiment, the nature of interactions between mucin and dipalmitoylphosphatidylcholine (DPPC) components of the monolayers under physiological conditions, (characteristic of the vagina and oral cavity), was investigated. It has been shown that at pH 4.2 mucin molecules reveal a strong affinity to the model biomembrane, composed of zwitterionic DPPC, and probably interact with it through the hydrophobic interactions. At pH 6.8 very weak electrostatic interactions are possible between the positively charged quaternary ammonium groups present in the DPPC molecules and the negatively charged mucin molecules. Moreover, from the relaxation experiment we concluded that beneath the DPPC layer there is a layer made of mucin particles due to electrostatic attraction. This layer of mucin beneath the DPPC particles stabilizes the entire system, especially at physiologically significant surface pressure, i.e. at pi = 30 mN/m.