Importance of the carboxy-terminal 25 amino acid residues of lung collectins in interactions with lipids and alveolar type II cells.
Surfactant proteins A and D (SP-A and SP-D) are structurally related members of the collectin family found in the alveolar compartment of the lung. SP-A binds dipalmitoylphosphatidylcholine (DPPC) and galactosylceramide (GalCer), induces liposome aggregation, and regulates the uptake and secretion of surfactant lipids by alveolar type II cells in vitro. SP-D binds phosphatidylinositol (PI) and glucosylceramide. The purpose of this study was to identify a critical stretch of primary sequence in the SP-A region Cys(204)-Phe(228) and the SP-D region Cys(331)-Phe(355) that is involved in protein-specific lipid and type II cell interactions. Chimeras ad1 and ad2 were constructed with rat SP-A/SP-D splice junctions at Cys(218)/Gly(346) and Lys(203)/Cys(331), respectively. Chimera ad1 but not ad2 retained DPPC liposome binding activity. Both chimeras retained significant binding to GalCer liposomes. Chimera ad1 did not bind to PI, whereas chimera ad2 acquired a significant PI binding. Both chimeras failed to induce liposome aggregation and to interact with alveolar type II cells. In addition, monoclonal antibody 1D6 that blocks specific SP-A functions did not recognize either chimera. From these results, we conclude that (1) the SP-A region Leu(219)-Phe(228) is required for liposome aggregation and interaction with alveolar type II cells, (2) the SP-A region Cys(204)-Cys(218) is required for DPPC binding, (3) the SP-D region Cys(331)-Phe(355) is essential for minimal PI binding, and (4) the epitope for mAb 1D6 is located at the region contiguous to the SP-A region Leu(219)-Phe(228).
Saitoh
M
M
Department of Biochemistry, Sapporo Medical University School of Medicine, Sapporo, Japan.
Sano
H
H
Chiba
H
H
Murakami
S
S
Iwaki
D
D
Sohma
H
H
Voelker
D R
DR
Akino
T
T
Kuroki
Y
Y
D015060:1,2-Dipalmitoylphosphatidylcholine / Q000378:metabolism; D000596:Amino Acids / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D000818:Animals; D000911:Antibodies, Monoclonal / Q000378:metabolism; D001666:Binding Sites, Antibody; D002352:Carrier Proteins / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D037222:Collectins; D006023:Glycoproteins / Q000235:genetics / Q000378:metabolism; D050356:Lipid Metabolism; D008055:Lipids / Q000235:genetics / Q000502:physiology*; D008081:Liposomes / Q000378:metabolism; D008168:Lung / Q000166:cytology / Q000378:metabolism / Q000502:physiology*; D008297:Male; D010446:Peptide Fragments / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D011510:Proteolipids / Q000037:antagonists & inhibitors / Q000235:genetics / Q000276:immunology / Q000378:metabolism; D011650:Pulmonary Alveoli / Q000166:cytology / Q000378:metabolism*; D037662:Pulmonary Surfactant-Associated Protein A; D037663:Pulmonary Surfactant-Associated Protein D; D037661:Pulmonary Surfactant-Associated Proteins; D011663:Pulmonary Surfactants / Q000037:antagonists & inhibitors / Q000235:genetics / Q000276:immunology / Q000378:metabolism; D051381:Rats; D017207:Rats, Sprague-Dawley; D011993:Recombinant Fusion Proteins / Q000037:antagonists & inhibitors / Q000737:chemistry / Q000276:immunology / Q000378:metabolism
D000596:Amino Acids; D000911:Antibodies, Monoclonal; D002352:Carrier Proteins; D037222:Collectins; D006023:Glycoproteins; D008055:Lipids; D008081:Liposomes; D010446:Peptide Fragments; D011510:Proteolipids; D037662:Pulmonary Surfactant-Associated Protein A; D037663:Pulmonary Surfactant-Associated Protein D; D037661:Pulmonary Surfactant-Associated Proteins; D011663:Pulmonary Surfactants; D011993:Recombinant Fusion Proteins; D015060:1,2-Dipalmitoylphosphatidylcholine