Conformation of mucous glycoproteins in aqueous solvents

Light‐scattering techniques have been used to measure the z‐average radius of gyration R g z‐average translational diffusion coefficient D t and weight–average molecular weight M w of porcine submaxillary mucin (PSM) in solution. PSM isolated at low shear in the presence of protease inhibitors has a M w about twice as large as a sample prepared without these precautions. The former sample has a M w of 17 × 10 6 in 0.1 M NaCl, which decreases to 8 × 10 6 in 6 M guanidine hydrochloride (GdnHCl) and then to 2 × 10 6 on addition of 0.1 M mercaptoethanol to the 6 M GdnHCl solution. The R g or D values obtained for PSM in this work superimpose with those of other authors for different mucin glycoproteins, leading to linear log–log relationships to the molecular weight of the protein core. Comparison of these results with those in the literature for denatured proteins suggest that mucins are linear random coils in which the protein core is stiffened by the presence of the oligosaccharide side chains. The length of the oligosaccharides and the nature of the solvent have little effect on the extension of the protein core. This suggests that the stiffness of the protein core is maintained by steric repulsion of the residues at the beginning of the oligosaccharide chains.