Alveolyn--structure and source: a review.

Alveolyn is a unique secretory glycoprotein of 250,000 molecular weight (MW) that is found in distal pulmonary secretions. Several glycoproteins of 130,000 MW, 80,000 MW, 62,000 MW, and 36,000 MW have also been found to be present in the alveolar secretions, and it was found that these glycoproteins were proteolytic fragments of the much larger molecular glycoprotein. It is also a major protein in human amniotic fluid, presumably a product of alveolar secretions. It is also secreted by a clone of pulmonary fetal type II cells. Preliminary results indicate that two of the proteolytic fragments of 62,000 MW and 36,000 MW contain alternate collagenous and noncollagenous domains in the same polypeptide chain. The presence of collagenous domains in these glycoproteins was also confirmed by their susceptibility to digestion with collagenase and the presence of Gly-Pro-Hyp-Gly-type sequence in the peptide chain. Very little is known about the tertiary structure of the protein, except that its fragments bind phospholipids and probably facilitate transfer of the lipid to air-water interfaces.