Pulmonary surfactant protein D specifically binds to phosphatidylinositol.
Alveolar type II cells produce and secrete a complex mixture of lipids and proteins called pulmonary surfactant of which phospholipids are the major components. Surfactant proteins (SP) A, B, and C interact with phospholipids and are believed to play important roles in alveolar spaces. However, whether surfactant protein D (SP-D) interacts with phospholipids is unknown. In the present study, we examined whether SP-D binds to phospholipids and investigated phospholipid specificities of SP-D binding and the structural requirements of phospholipids for that binding using 125I-SP-D as a probe. 125I-SP-D bound exclusively to phosphatidylinositol (PI) in various phospholipids or a fraction containing phospholipids extracted from surfactant, which were developed on thin layer chromatography. 125I-SP-D also bound to PI coated on microtiter wells in a manner dependent upon the SP-D concentration. Unlabeled SP-D competed well with 125I-SP-D for PI binding and the antibody against SP-D abolished 125I-SP-D binding to PI. PI liposome also attenuated 125I-SP-D binding to the solid phase PI. Ca2+ is absolutely required for the binding of SP-D to PI. SP-D failed to bind to lyso-PI, fatty acids derived from PI digested with phospholipase A2, or diacylglycerol obtained after phospholipase C treatment of PI. SP-D bound to neither phosphatidylinositol 4-monophosphate nor phosphatidylinositol 4,5-diphosphate. We conclude that SP-D specifically binds to PI. This is the first report that demonstrates that SP-D interacts with surfactant phospholipids.
Ogasawara
Y
Y
Department of Biochemistry, Sapporo Medical College, Japan.
Kuroki
Y
Y
Akino
T
T
D000818:Animals; D001992:Bronchoalveolar Lavage Fluid / Q000378:metabolism; D002846:Chromatography, Affinity; D002855:Chromatography, Thin Layer; D004591:Electrophoresis, Polyacrylamide Gel; D006023:Glycoproteins / Q000302:isolation & purification / Q000378:metabolism*; D007700:Kinetics; D008081:Liposomes; D010716:Phosphatidylinositols / Q000378:metabolism*; D010743:Phospholipids / Q000302:isolation & purification / Q000494:pharmacology; D037663:Pulmonary Surfactant-Associated Protein D; D011663:Pulmonary Surfactants / Q000302:isolation & purification / Q000378:metabolism*; D051381:Rats
D006023:Glycoproteins; D008081:Liposomes; D010716:Phosphatidylinositols; D010743:Phospholipids; D037663:Pulmonary Surfactant-Associated Protein D; D011663:Pulmonary Surfactants