CP4: a pneumocyte-derived collagenous surfactant-associated protein. Evidence for heterogeneity of collagenous surfactant proteins.
Type II pneumocytes secrete pulmonary surfactant and are known to synthesize SP-35, a collagenous surfactant-associated protein. Freshly isolated type II cells also synthesize other bacterial collagenase-sensitive and hydroxyproline-containing proteins, including a glycoprotein designated CP4. CP4 was isolated from rat pneumocyte culture medium by immune precipitation with polyclonal antibodies to rat surfactant proteins or by DEAE chromatography and reverse-phase or gel permeation HPLC. CP4 did not cross-react with polyclonal antibodies to SP-35 and was completely resolved from SP-35 by SDS-PAGE (Mr 43K reduced) or isoelectric focusing. Unlike SP-35, which consists of acidic isoforms assembled as disulfide-bonded dimers and multimers, CP4 was secreted as basic isoforms assembled as disulfide-bonded trimers. Differences in primary structure were demonstrated by CNBr and V8 protease peptide mapping. The secretion of both proteins was inhibited by 2,2'-dipyridyl, an inhibitor of posttranslational prolyl and lysyl hydroxylation and collagen triple helix formation. CP4 was isolated from EDTA extracts of rat surfactant. These studies provide evidence for the heterogeneity of pneumocyte-derived collagenous surfactant-associated proteins.
Persson
A
A
Department of Pathology, Jewish Hospital, Washington University School of Medicine, St. Louis, Missouri 63110.
Rust
K
K
Chang
D
D
Moxley
M
M
Longmore
W
W
Crouch
E
E
D000818:Animals; D002478:Cells, Cultured; D002851:Chromatography, High Pressure Liquid; D003094:Collagen; D004220:Disulfides / Q000032:analysis; D004591:Electrophoresis, Polyacrylamide Gel; D006909:Hydroxyproline / Q000032:analysis; D007525:Isoelectric Focusing; D008168:Lung / Q000166:cytology / Q000378:metabolism*; D046911:Macromolecular Substances; D008297:Male; D008970:Molecular Weight; D010449:Peptide Mapping; D011663:Pulmonary Surfactants / Q000302:isolation & purification*; D051381:Rats; D011919:Rats, Inbred Strains
D004220:Disulfides; D046911:Macromolecular Substances; D011663:Pulmonary Surfactants; D003094:Collagen; D006909:Hydroxyproline