Synthesis of surfactant-associated protein, 35,000 daltons, in fetal lung.
The major human pulmonary surfactant-associated protein of 35,000 daltons (Da) (SAP-35), consists of a group of related proteins of 27,000-36,000 Da, with isoelectric points ranging from pH 4.6 to 5.2. SAP-35 precursors were identified by immunoprecipitation of protein products of in vitro translation of normal adult human poly(A)+ mRNA with human SAP-35 antiserum. The translation products nearly comigrated with the most basic components of alveolar SAP-35 (mol mass = 24,500-27,000 Da). Processing of the primary translation products by canine pancreatic microsomal membranes increased their apparent molecular weight to 29,000-30,000-Da forms, which were sensitive to endoglycosidase F, suggesting the addition of asparagine-linked oligosaccharides to the molecules. A smaller protein of 24,500 Da was generated during treatment with canine microsomal membranes likely representing cleavage of a signal peptide. SAP-35 was not detected in explants of [35S]methionine-labeled fetal lung (20-24 wk gestation) after 1 day of culture or immunoprecipitates of in vitro translated poly(A)+ mRNA isolated from fetal human lung. However, after 3-5 days of organ culture, synthesis of SAP-35 was readily detected by immunoprecipitation of [35S] methionine-labeled tissue. Fully sialylated (neuraminidase-sensitive forms) comigrated with fully glycosylated SAP-35 isolated from human surfactant. High mannose (endoglycosidase H-sensitive precursors) were also synthesized by the organ cultures and were distinct from the secreted form in surfactant. Synthesis of surfactant-associated SAP-35 and its precursors was induced in association with morphological maturation of the type II epithelial cell during organ culture of human fetal lung.
D055598:Chemical Phenomena; D002621:Chemistry; D005333:Fetus / Q000378:metabolism*; D006801:Humans; D008168:Lung / Q000196:embryology / Q000378:metabolism* / Q000648:ultrastructure; D008854:Microscopy, Electron; D008970:Molecular Weight; D009924:Organ Culture Techniques; D011061:Poly A / Q000235:genetics; D014176:Protein Biosynthesis; D011510:Proteolipids / Q000096:biosynthesis*; D037662:Pulmonary Surfactant-Associated Protein A / Q000031:analogs & derivatives*; D037661:Pulmonary Surfactant-Associated Proteins; D011663:Pulmonary Surfactants / Q000096:biosynthesis*; D012333:RNA, Messenger / Q000235:genetics
D011510:Proteolipids; D037662:Pulmonary Surfactant-Associated Protein A; D037661:Pulmonary Surfactant-Associated Proteins; D011663:Pulmonary Surfactants; D012333:RNA, Messenger; C445842:SFTPA1 protein, human; D011061:Poly A