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Characterization of human middle ear mucus glycoprotein in chronic secretory otitis media (CSOM)
J E FitzGerald1, G G Green, F W Stafford
1Department of Physiological Sciences, University of Newcastle upon Tyne, Medical School, UK.
Abstract:
Middle ear effusion was obtained from children with chronic secretory otitis media undergoing myringotomy. The effusions contained about 120 mg/ml non-dialysable solids, of which 18-31% was mucus glycoprotein. The purified mucus glycoprotein had a composition characteristic of other mucus glycoproteins. Amino acid analysis of the glycoprotein indicates a protein core consisting of glycosylated regions resistant to proteolysis and non-glycosylated regions susceptible to proteolysis. Analysis of the mucus glycoprotein by gel filtration on Sepharose 2B showed that reduction caused a decrease in hydrodynamic size and proteolysis caused a further decrease. The difference was confirmed by sedimentation coefficient and viscosity measurements. The reduced glycoprotein had an intrinsic viscosity of 0.113 ml/mg and an S0(20) of 15.2S compared to a value of 0.018 ml/mg and 9.6S for the proteolytically digested glycoprotein. These results suggest a model for this middle ear mucus glycoprotein, in which the native glycoprotein is a large molecular mass polymer maintained by disulphide bridges. These disulphide linked glycoprotein units are broken down into smaller units by proteolysis. The mucus glycoprotein could not be purified completely free from low molecular mass components. A glycoprotein, susceptible to proteolysis Mr 28,000-33,000 co-fractionates with the major high molecular mass mucus glycoprotein.
Insights
Middle ear effusion mucus glycoproteins are large polymers stabilized by disulfide bonds. Proteolysis breaks these bonds, reducing molecular size and viscosity, offering insights into otitis media mucus composition.
Area of Science:
- Biochemistry
- Otolaryngology
- Glycobiology
Background:
- Chronic secretory otitis media is characterized by middle ear effusion.
- Middle ear effusion contains significant amounts of mucus glycoprotein.
Purpose of the Study:
- To characterize the biochemical properties of mucus glycoproteins from middle ear effusion.
- To elucidate the structural organization and molecular assembly of middle ear mucus glycoproteins.
Main Methods:
- Purification and analysis of mucus glycoprotein from middle ear effusion.
- Gel filtration chromatography (Sepharose 2B), reduction, and proteolysis.
- Viscosity and sedimentation coefficient measurements.
Main Results:
- Middle ear effusion mucus glycoprotein is a high molecular mass polymer (18-31% of non-dialysable solids).
- The glycoprotein has a protein core with glycosylated and non-glycosylated regions.
- Disulfide bonds maintain the polymeric structure; reduction and proteolysis decrease molecular size and viscosity.
Conclusions:
- Middle ear mucus glycoprotein is a disulfide-linked polymer.
- Proteolytic activity may contribute to the breakdown of mucus structure in otitis media.
- A lower molecular weight glycoprotein (28,000-33,000 Da) co-fractionates with the main mucus glycoprotein.