The mannose-binding protein A region of glutamic acid(185)-alanine(221) can functionally replace the surfactant protein A region of glutamic acid(195)-phenylalanine(228) without loss of interaction with lipids and alveolar type II cells
The mannose-binding protein A region of glutamic acid(185)-alanine(221) can functionally replace the surfactant protein A region of glutamic acid(195)-phenylalanine(228) without loss of interaction with lipids and alveolar type II cells
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DOI：
10.1021/bi962967e
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发表时间：
1997-06-10
期刊：
影响因子：
2.9
通讯作者：
Akino, T
中科院分区：
文献类型：
--
作者：
Honna, T;Kuroki, Y;Akino, T
肺表面活性剂蛋白 A (SP-A) 是一种 C 型凝集素，调节 II 型肺泡细胞对表面活性剂脂质的摄取和分泌，并结合二棕榈酰磷脂酰胆碱 (DPPC) 和半乳糖神经酰胺 (GalCer)。我们从大鼠血清中分离出甘露糖结合蛋白 A (MBP-A)，其结构与 SP-A 类似，并检查其在功能上是否与 SP-A 等效。我们发现MBP-A不具备与脂质和II型细胞相互作用的能力。本研究的目的是通过使用与 MBP-A 的嵌合蛋白来研究参与结合脂质并与 II 型细胞相互作用的 SP-A 区域。嵌合体 AM1、AM2 和 AM3 分别在 Cys(218)/Gln(210)、Lys(203)/Cys(195) 和 Gly(194)/Glu(185) 处通过 SP-A/MBP 剪接点构建。所有嵌合体均结合 DPPC 和 GalCer，其活性与重组 SP-A 相当。这三种嵌合体保留了诱导磷脂囊泡聚集和增加 II 型细胞脂质摄取的能力，尽管程度低于野生型 SP-A。嵌合体以0.5μg/mL的IC50抑制IT型细胞的脂质分泌，并有效竞争SP-A受体结合。此外，所有这些嵌合体均含有单克隆抗体 1D6 的表位，该表位可阻断特定的 SP-A 功能。从这些结果中，我们得出结论，Glu(185)-Ala(221) 的 MBP-A 区域可以在功能上取代 Glu(195)-Phe(228) 的同源 SP-A 区域，而不会失去与脂质和 II 型细胞的相互作用。
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 Cys(218)/Gln(210), Lys(203)/Cys(195), and Gly(194)/Glu(185), 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 IT cells with an IC50 Of 0.5 mu g/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 Glu(185)-Ala(221) can functionally replace the homologous SP-A region of Glu(195)-Phe(228) without loss of interaction with lipids and type II cells.