title: Atomic force microscopy reveals aggregation of gastric mucin at low pH.
abstract: Mammalian gastric mucin, at high concentration, is known to form a gel at low pH, behavior essential to the protection of the stomach from auto-digestion. Atomic force microscopy (AFM) measurements of dilute solutions of porcine gastric mucin in an aqueous environment in the pH range 6-2 provide a direct visualization of extended fiberlike molecules at pH 6 that aggregate at pH 4 and below forming well-defined clusters at pH 2. The clusters consist of 10 or less molecules. AFM images of mucin at high concentration at pH 2 reveal clusters similar to those seen in the dilute solutions at low pH. We also imaged human gastric mucus revealing a network having a "pearl necklace" structure. The "pearls" are similar in size to the clusters found in the purified porcine gastric mucin gels. AFM images of deglycosylated mucin reveal that the deglycosylated portions of the molecule re-fold into compact, globular structures suggesting that the oligosaccharide chains are important in maintaining the extended conformation of mucin. However, the oligosaccharides do not appear to be directly involved in the aggregation at low pH, as clusters of similar size are observed at pH 2 in both native and deglycosylated mucin.
authors.affiliation: Department of Physics, Boston University, Boston, Massachusetts 02215, USA.
authors.forename: Zhenning
authors.initials: Z
authors.lastname: Hong
authors.forename: Bernard
authors.initials: B
authors.lastname: Chasan
authors.forename: Rama
authors.initials: R
authors.lastname: Bansil
authors.forename: Bradley S
authors.initials: BS
authors.lastname: Turner
authors.forename: K Ramakrishnan
authors.initials: KR
authors.lastname: Bhaskar
authors.forename: Nezam H
authors.initials: NH
authors.lastname: Afdhal
mesh_terms: D000818:Animals; D001671:Biochemistry / Q000379:methods*; D005752:Gastric Mucins / Q000737:chemistry*; D005753:Gastric Mucosa / Q000378:metabolism / Q000648:ultrastructure*; D006031:Glycosylation; D006801:Humans; D006863:Hydrogen-Ion Concentration; D021621:Imaging, Three-Dimensional; D046911:Macromolecular Substances; D018625:Microscopy, Atomic Force; D008968:Molecular Conformation; D008970:Molecular Weight; D011485:Protein Binding; D011487:Protein Conformation; D012996:Solutions; D013270:Stomach / Q000648:ultrastructure; D013552:Swine; D014783:Viscosity
chemical_list: D005752:Gastric Mucins; D046911:Macromolecular Substances; D012996:Solutions