The mannose-binding protein A region of glutamic acid185-alanine221 can functionally replace the surfactant protein A region of glutamic acid195-phenylalanine228 without loss of interaction with lipids and alveolar type II cells.
Pulmonary surfactant protein A (SP-A) is a C-type lectin that regulates the uptake and secretion of surfactant lipids by alveolar type II cells and binds dipalmitoylphosphatidylcholine (DPPC) and galactosylceramide (GalCer). We isolated mannose-binding protein A (MBP-A) from rat sera, which is structurally analogous to SP-A, and examined if it was functionally equivalent to SP-A. We found that MBP-A did not possess the ability to interact with lipids and type II cells. The purpose of this study was to investigate the SP-A region involved in binding lipids and interacting with type II cells by using chimeric proteins with MBP-A. Chimeras AM1, AM2, and AM3 were constructed with SP-A/MBP splice junctions at Cys218/Gln210, Lys203/Cys195, and Gly194/Glu185, respectively. All of the chimeras bound DPPC and GalCer with activity comparable to recombinant SP-A. The three chimeras retained the ability to induce phospholipid vesicle aggregation and augment lipid uptake by type II cells, albeit to a lesser extent than wild type SP-A. The chimeras inhibited lipid secretion from type II cells with an IC50 of 0.5 microg/mL and competed effectively for SP-A receptor binding. In addition all these chimeras contained the epitope for monoclonal antibody 1D6, which blocks specific SP-A function. From these results, we conclude that the MBP-A region of Glu185-Ala221 can functionally replace the homologous SP-A region of Glu195-Phe228 without loss of interaction with lipids and type II cells.
Honma
T
T
Department of Biochemistry, Sapporo Medical University School of Medicine, Chuo-ku, Japan.
Kuroki
Y
Y
Tsunezawa
W
W
Ogasawara
Y
Y
Sohma
H
H
Voelker
D R
DR
Akino
T
T
D000209:Acute-Phase Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D000409:Alanine / Q000737:chemistry* / Q000378:metabolism; D000818:Animals; D000911:Antibodies, Monoclonal / Q000378:metabolism; D002352:Carrier Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D004591:Electrophoresis, Polyacrylamide Gel; D018604:Epitope Mapping; D018698:Glutamic Acid / Q000737:chemistry* / Q000378:metabolism; D006023:Glycoproteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D050356:Lipid Metabolism; D008358:Mannose / Q000378:metabolism*; D037601:Mannose-Binding Lectin; D010649:Phenylalanine / Q000737:chemistry* / Q000378:metabolism; D011510:Proteolipids / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D011650:Pulmonary Alveoli / Q000737:chemistry / Q000166:cytology* / Q000378:metabolism; D037662:Pulmonary Surfactant-Associated Protein A; D037661:Pulmonary Surfactant-Associated Proteins; D011663:Pulmonary Surfactants / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D051381:Rats; D017207:Rats, Sprague-Dawley; D011993:Recombinant Fusion Proteins / Q000276:immunology / Q000378:metabolism
D000209:Acute-Phase Proteins; D000911:Antibodies, Monoclonal; D002352:Carrier Proteins; D006023:Glycoproteins; D037601:Mannose-Binding Lectin; D011510:Proteolipids; D037662:Pulmonary Surfactant-Associated Protein A; D037661:Pulmonary Surfactant-Associated Proteins; D011663:Pulmonary Surfactants; D011993:Recombinant Fusion Proteins; C069858:mannose binding protein A; D018698:Glutamic Acid; D010649:Phenylalanine; D000409:Alanine; D008358:Mannose