Molecular mechanism of the regulation by binding of surfactant protein A and D to their receptors and lung diseases.

肺表面活性物质是一种脂质和蛋白质的混合物，由肺泡II型细胞合成并分泌到肺泡腔。肺表面活性蛋白A和D（SP-A和SP-D）在肺磷脂平衡和宿主防御中发挥重要作用。在本研究中，我们专注于SP-A和SP-D的功能作用，以及SP-A结合蛋白（annexin IV）1。SP-A和SP-D是同源蛋白，属于C型凝集素家族。两种蛋白质都与磷脂和糖脂结合：SP-A与二Parmitoylphosphatidylcholine（DPPC）和GalCer结合，SP-D与磷脂酰肌醇（PI）和GluCer结合。SP-A还抑制肺泡II型细胞的磷脂分泌，并通过SP-A受体增加磷脂的摄取，而SP-D不具有这些特性。使用具有SP-A和SP-D的嵌合蛋白，揭示了<195>SP-A的C-末端的Glu对SP-A的功能性质是重要的，并且SP-A的C-末端的Glu对SP-A的<321>C-末端和SP-D的<261>C-末端的Cys对SP-A的功能性质是重要的。 ...更多信息 SP-D分别是PI结合和GluCer结合所必需的.膜联蛋白IV是膜联蛋白家族的成员，其由独特的N-末端和C-末端核心区组成。核心区由4个共有的70个氨基酸重复序列（结构域1-4）组成，其中有Ca^2+和磷脂结合位点。利用膜联蛋白IV的截短突变体，发现SP-A的结合位点位于膜联蛋白IV的结构域3。此外，通过定点突变研究，还发现膜联蛋白IV结构域3的Ca^2+结合位点<197>和SP-A的Arg^对Ca^2+依赖性结合也很重要. SP-A已被证明与革兰氏阴性菌相互作用。由于LPS是细菌膜的主要成分，我们研究了SP-A与LPS之间可能的相互作用。结果表明，SP-A与粗糙的LPS和脂质A结合，但不与光滑的LPS结合。SP-A可以减弱LPS诱导的TNF-α表达的增加。SP-A还与光滑的LPS受体CD 14相互作用。因此，SP-A通过与LPS竞争CD 14来抑制LPS诱导的TNF-α表达。少

Pulmonary surfactant, a mixture of lipids and proteins, is synthesized by alveolar type II cells and secreted to alveolar space. Surfactant proteins A and D (SP-A and SP-D) have been shown to play roles in phospholipid homeostasis and host defense in lung. In the present study, we focused on the functional roles of SP-A and SP-D, and on the SP-A binding protein (annexin IV)1. SP-A and SP-D are homologous proteins and belong to the C-type lectin family. Both proteins bind to phospoholipids and glycolipids : SP-A to diparmitoylphosphatidylcholine (DPPC) and GalCer, and SP-D to phosphtidylinositol (PI) and GluCer. SP-A also inhibits phospholipid secretion by alveolar type II cells and augments uptake of phospohlipids via SP-A receptors, whereas SP-D does not have these properties. Using chimeric proteins with SP-A and SP-D, it was revealed that Glu^<195> to C-terminus of SP-A is important for the functional properties of SP-A and that Glu^<321> to C-terminus and Cys^<261> to C-terminus of … More SP-D are required for PI binding and GluCer binding, respectively.2. Annexin IV is a member of the annexin family that consists of a unique N-terminal and a C-terminal core region. The core region consists of four consensus 70 amino acid-repeats (domains 1-4), in which Ca^<2+> and phospholipid binding sites are located. Using truncation mutants of annexin IV, SP-A binding site was shown to locate in domain 3 of annexin IV.Moreover, the Ca^<2+>-binding site in domain 3 of annexin IV and Arg^<197> of SP-A were also shown to be important for Ca^<2+>-dependent binding by site-directed mutagenesis study.3. SP-A has been shown to interact with the Gram-negative bacteria. As LPS is the main constituent of the bacterial membrane, we investigate possible interaction between SP-A and LPS.It was revealed that SP-A bound to both rough LPS and lipid A but not to smooth LPS.LPS-induced augmentation of expression of TNF-alpha was attenuated by SP-A.SP-A was also shown to interact with CD14, which is the smooth LPS receptor. Therefore, SP-A inhibited LPS-induced TNF-alpha expression by competing with LPS for CD14. Less