Glycobiology Advance Access published online on March 13, 2008
Glycobiology, doi:10.1093/glycob/cwn024
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Analyzing the functions of large glycoconjugates through the dissipative properties of their absorbed layers using the gel-forming mucin MUC5B as an example
Department of Biochemistry and Biophysics, University of North Carolina at Chapel Hill, Chapel Hill, NC. 27599, USA
* Corresponding Author: Email : kesimer{at}med.unc.edu, Phone: 9198432577, Fax : 9199667524
Received on January 9, 2008; accepted on March 10, 2008
Glyconjugates such as mucins, proteoglycans and polysaccharides form the structural basis of protective cell-surface layers. In particular gel-forming mucins define a zone between the epithelial cell layer and the environment. Such molecules are of extreme molecular weight 5–100x106 and size (Rg 20–300nm). On this account their biochemistry is inseparable from their physical biochemistry. Combining laser light scattering and quartz crystal mass balance with dissipation methods (QCM-D) we have investigated the properties of the MUC5B mucin and its cognate fragments when bound to a hydrophobic surface. MUC5B forms the basis of gels responsible for the protection of the oral cavity, lung and cervical canal surfaces. Here we show, by analyzing dissipative interactions of hydrophobic, gold and polystyrene surfaces, with the intact MUC5B molecule, its reduced subunits and glycosylated tryptic fragments (obtained after reduction) the formation of 40–100nm thick highly structured, hydrated interfaces. These interfaces are dominated in their geometry and dissipative properties by the negatively charged carbohydrate-rich domains of the molecule, the naked protein domains being responsible for attachment. These carbohydrate-rich surfaces have well defined absorptive properties and permit the entry and entrapment of albumin coated micro-beads into the absorbed layer at and below a size of 60nm. However beads larger than 100nm are completely excluded from the surfaces. These absorptive phenomena correlate with large changes in film dissipation and thus may not only be important in biological functions e.g. binding viruses but could well be informative to the surfaces (often ciliated) onto which such mucus films are attached.
Key words: Adhesion / MUC5B / Mucin / Mucus / QCM-D