Macromolecular properties and polymeric structure of mucus glycoproteins

Mucus glycoproteins (mucins) were isolated from cervical and gastric mucus as well as from chronic bronchitic sputum. The mucus gel was solubilized by slow stirring in 6M-guanidinium chloride supplemented with low-Mr proteinase inhibitors. Subsequent removal of non-mucin proteins and DNA was achieved with isopycnic density-gradient centrifugation. The cervical and the respiratory mucins were of similar size (Mr about 10 X 10(6) and 18 X 10(6)), respectively), whereas the gastric mucins were considerably larger (Mr about 45 X 10(6)). 'Subunits' isolated after disulphide bond cleavage were the same size for the three mucins, as were glycopeptides obtained after subsequent trypsin digestion of the subunits. Physical data suggest that the respiratory and gastric mucins conform to the model for the polymeric structure proposed previously for cervical mucins. The macromolecules are described as linear flexible chains behaving, in dilute solution, as random coils. We propose that mucus glycoproteins are considerably larger than hitherto recognized and that mucins of various origins are very similar in their macromolecular properties and polymeric structure.