Sialic acid of lung surfactant apoprotein, SP 28-36, is not required for the Ca2+-mediated interactions between surfactant lipids and SP 28-36.

We examined whether removal of sialic acid from the lung surfactant apoprotein (SP 28-36) affected certain properties of reassembled surfactant lipid-SP 28-36 complexes. SP 28-36 was treated with neuraminidase and then added to liposomes made from extracted surfactant lipids. We found that in the presence of Ca2+ the asialoprotein was as effective as the native SP 28-36 in binding to surfactant lipids, causing aggregation and promoting rapid surface film formation.