期刊
JOURNAL OF BIOLOGICAL CHEMISTRY
卷 277, 期 30, 页码 26971-26979出版社
AMER SOC BIOCHEMISTRY MOLECULAR BIOLOGY INC
DOI: 10.1074/jbc.M110080200
关键词
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资金
- NHLBI NIH HHS [HL 63329, HL 61646, HL 61612, HL 58795] Funding Source: Medline
The N-terminal domains of the lung collectins, surfactant proteins A (SP-A) and D (SP-D), are critical for surfactant phospholipid interactions and surfactant homeostasis, respectively. To further assess the importance of lung collectin N-terminal domains in surfactant structure and function, a chimeric SP-D/SP-A (D/A) gene was constructed by substituting nucleotides encoding amino acids Asn(1)-Ala(7) of rat SP-A with the corresponding N-terminal sequences from rat SP-D, Ala(1)-Asn(25). Recombinant D/A migrated as a 35-kDa band on reducing SDS-PAGE and as a ladder of disulfide-linked multimers under nonreducing conditions. The recombinant D/A bound and aggregated phosphatidylcholine containing vesicles as effectively as rat SP-A. Mice in which endogenous pulmonary collectins were replaced with D/A were developed by human SP-C promoter-driven overexpression of the D/A gene in SP-A(-/-) and SP-D-/- animals. Analysis of lavage fluid from SP-A(-/-) D/A mice revealed that glycosylated, oligomeric D/A was secreted into the air spaces at levels that were comparable with the authentic collectins and that the N-terminal interchange converted SP-A from a bouquet to a cruciform configuration. Transmission electron microscopy of surfactant from the SP-A(-/-,D/A) mice revealed atypical tubular myelin containing central target-like electron density. Surfactant isolated from SP-A(-/-,D/1) mice exhibited elevated surface tension both in the presence and absence of plasma inhibitors, but whole lung compliance of the SP-A(-/-,D/A) animals was not different from the SP-A(-/-) littermates. Lung-specific overexpression of D/A in the SPD-/- mouse resulted in hetero-oligomer formation with mouse SP-A and did not correct the air space dilation or phospholipidosis that occurs in the absence of SP-D. These studies indicate that the N terminus of SP-D 1) can functionally replace the N terminus of SP-A for lipid aggregation and tubular myelin formation, but not for surface tension lowering properties of SP-A, and 2) is not sufficient to reverse the structural and metabolic pulmonary defects in the SP-D-/- mouse.
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