title: Molecular Structure and Equilibrium Forces of Bovine Submaxillary Mucin Adsorbed at a Solid-Liquid Interface.
abstract: By combining dynamic light scattering, circular dichroism spectroscopy, atomic force microscopy, and surface force apparatus, the conformation of bovine submaxillary mucin in dilute solution and nanomechanical properties of mucin layers adsorbed on mica have been investigated. The samples were prepared by additional chromatographic purification of commercially available products. The mucin molecule was found to have a z-average hydrodynamic diameter of ca. 35 nm in phosphate buffered solution, without any particular secondary or tertiary structure. The contour length of the mucin is larger than, yet of the same order of magnitude as the diameter, indicating that the molecule can be modeled as a relatively rigid polymeric chain due to the large persistence length of the central glycosylated domain. Mucin molecules adsorbed abundantly onto mica from saline buffer, generating polymer-like, long-ranged, repulsive, and nonhysteretic forces upon compression of the adsorbed layers. Detailed analysis of such forces suggests that adsorbed mucins had an elongated conformation favored by the stiffness of the central domain. Acidification of aqueous media was chosen as means to reduce mucin-mucin and mucin-substrate electrostatic interactions. The hydrodynamic diameter in solution did not significantly change when the pH was lowered, showing that the large persistence length of the mucin molecule is due to steric hindrance between sugar chains, rather than electrostatic interactions. Remarkably, the force generated by an adsorbed layer with a fixed surface coverage also remained unaltered upon acidification. This observation can be linked to the surface-protective, pH-resistant role of bovine submaxillary mucin in the variable environmental conditions of the oral cavity.
authors: †Consiglio Nazionale delle Ricerche - Istituto di Nanotecnologia (CNR-Nanotec) and LICRYL c/o Dipartimento di Fisica, Università della Calabria, cubo 33/B, Rende (CS) 87036 Italy.
authors: Bruno
authors: B
authors: Zappone
authors: §Dipartimento di Fisica, Università della Calabria, cubo 31/C, Rende (CS) 87036 Italy.
authors: Navinkumar J
authors: NJ
authors: Patil
authors: ‡Department of Mechanical Engineering, Technical University of Denmark, DK-2800, Kgs. Lyngby, Denmark.
authors: Jan B
authors: JB
authors: Madsen
authors: ‡Department of Mechanical Engineering, Technical University of Denmark, DK-2800, Kgs. Lyngby, Denmark.
authors: Kirsi I
authors: KI
authors: Pakkanen
authors: ‡Department of Mechanical Engineering, Technical University of Denmark, DK-2800, Kgs. Lyngby, Denmark.
authors: Seunghwan
authors: S
authors: Lee
mesh_terms: D000327:Adsorption; D000538:Aluminum Silicates / Q000737:chemistry*; D000818:Animals; D002417:Cattle; D057446:Hydrodynamics; D006863:Hydrogen-Ion Concentration; D015394:Molecular Structure; D009077:Mucins / Q000737:chemistry*; D012996:Solutions; D055672:Static Electricity; D013499:Surface Properties
chemical_list: D000538:Aluminum Silicates; C115439:BSM1 protein, Bos taurus; D009077:Mucins; D012996:Solutions; C011934:mica