Thermal stability and DPPC/Ca2+ interactions of pulmonary surfactant SP-A from bulk-phase and monolayer IR spectroscopy
Thermal stability and DPPC/Ca2+ interactions of pulmonary surfactant SP-A from bulk-phase and monolayer IR spectroscopy
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DOI：
10.1021/bi011188h
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发表时间：
2001-11-13
期刊：
影响因子：
2.9
通讯作者：
Flach, CR
中科院分区：
文献类型：
--
作者：
Bi, XH;Taneva, S;Flach, CR
表面活性蛋白A（SP-A）是肺表面活性物质中含量最丰富的蛋白质，参与多种生物学功能，包括表面活性物质稳态、生物物理活性和宿主防御。SP-A与脂质和Ca 2+形成三元复合物，这对蛋白质功能很重要。目前的研究使用红外（IR）透射光谱研究SPA，1，2-二棕榈酰磷脂酰胆碱（DPPC），和钙离子之间的体相相互作用沿着与红外反射吸收光谱（IRRAS）检查蛋白质的二级结构和脂质的取向顺序在单层膜原位在空气/水界面。SP-A的酰胺I轮廓揭示了1653和1636 cm（-1）处的两个特征，它们来自胶原样结构域，以及1645 cm（-1）处的一个广泛特征，表明它们来自碳水化合物识别结构域（CRD）。SP-A二级结构在脂质单层中不变。在DPPC或Ca 2+离子存在下SP-A的热变性揭示了一系列涉及胶原样区域的初始熔化的事件，随后形成分子间延伸形式。有趣的是，这些光谱变化在三元体系中受到抑制，这表明DPPC和Ca 2+的共同存在赋予SP-A显着的热稳定性。三元相互作用揭示了不对称羧酸伸缩振动的增强强度。IRRAS的测量表明，SP-A掺入到预先形成的DPPC单层在10 mN/m的表面压力诱导的平均酰基链倾斜角从35下降到28。相反，在25或40 mN/m的表面压力下观察到链倾斜的变化很小。这些结果与Keough及其同事[guano，M. L. F.、等人（1998）Biophys. J. 74，1101-1109]，其中建议SP-A在液体膨胀/液体冷凝边界处积聚。总之，这些实验揭示了SP-A在不同的生物相关环境中的显着稳定性。
Surfactant protein A (SP-A), the most abundant pulmonary surfactant protein, is implicated in multiple biological functions including surfactant homeostasis, biophysical activity, and host defense. SP-A forms ternary complexes with lipids and Ca2+ which are important for protein function. The current study uses infrared (IR) transmission spectroscopy to investigate the bulk-phase interaction between SPA, 1,2-dipalmitoylphosphatidylcholine (DPPC), and Ca2+ ions along with IR reflection-absorption spectroscopy (IRRAS) to examine protein secondary structure and lipid orientational order in monolayer films in situ at the air/water interface. The amide I contour of SP-A reveals two features at 1653 and 1636 cm(-1) arising from the collagen-like domain and a broad feature at 1645 cm(-1) suggested to arise from the carbohydrate recognition domain (CRD). SP-A secondary structure is unchanged in lipid monolayers. Thermal denaturation of SP-A in the presence of either DPPC or Ca2+ ion reveals a sequence of events involving the initial melting of the collagen-like region, followed by formation of intermolecular extended forms. Interestingly, these spectral changes were inhibited in the ternary system, showing that the combined presence of both DPPC and Ca2+ confers a remarkable thermal stability upon SP-A. The ternary interaction was revealed by the enhanced intensity of the asymmetric carboxylate stretching vibration. The IRRAS measurements indicated that incorporation of SP-A into preformed DPPC monolayers at a surface pressure of 10 mN/m induced a decrease in the average acyl chain tilt angle from 35 to 28. In contrast, little change in chain tilt was observed at surface pressures of 25 or 40 mN/m. These results are consistent with and extend the fluorescence microscopy studies of Keough and co-workers [guano, M. L. F., et al. (1998) Biophys. J. 74, 1101-1109] in which SP-A was suggested to accumulate at the liquid-expanded/liquid-condensed boundary. Overall these experiments reveal the remarkable stability of SP-A in diverse, biologically relevant environments.