Mapping and analysis of the lytic and fusogenic domains of surfactant protein B
Mapping and analysis of the lytic and fusogenic domains of surfactant protein B
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DOI：
10.1021/bi0485575
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发表时间：
2005-01-25
期刊：
影响因子：
2.9
通讯作者：
Weaver, TE
中科院分区：
文献类型：
--
作者：
Ryan, MA;Qi, XY;Weaver, TE
表面活性蛋白B(SP-B)是一种由79个氨基酸组成的疏水性多肽，调节肺内表面活性物质磷脂膜的结构和功能。在由DPPC/PG(7：3)组成的脂质体中加入SP-B会导致膜结合、失稳和融合，最终导致膜结构的重排。这项研究的目的是定位SP-B的融合和裂解结构域，并评估改变的融合和裂解对表面活性的影响。合成的多肽被用来预测SP-B的螺旋和/或螺旋间环，并测试融合、裂解和表面活性。SP-B的N-末端部分(残基1-37)除了螺旋1和2外，还包括非螺旋的N-末端氨基酸，促进脂质体的快速融合，而较短的多肽的效果明显较差。最佳表面张力降低的要求与融合相似；相反，仅螺旋1(7-22位残基)就足以裂解脂质体。SP-B的C-末端部分(残基43-79)包括螺旋3、4和5，与N-末端区域相比，其融合、裂解和表面张力降低活性显著降低。这些结果表明，SP-B的融合、裂解和表面活性主要映射到SP-B的N-末端。与SP-B的N-末端半部分对应的合成肽中的氨基酸取代表明，通常情况下，融合或裂解活性的降低与肽的表面张力降低性质的改变有关。然而，单靠融合和裂解活性的存在并不能解释SP-B的表面张力降低特性。我们提出了一个模型，在该模型中，螺旋1与脂类结合导致膜通透性而不是聚集；螺旋2介导膜的交联(聚集)，这反过来促进脂质混合、膜融合和界面吸附/表面张力降低。
Surfactant protein B (SP-B) is a hydrophobic, 79 amino acid peptide that regulates the structure and function of surfactant phospholipid membranes in the airspaces of the lung. Addition of SP-B to liposomes composed of DPPC/PG (7:3) leads to membrane binding, destabilization, and fusion, ultimately resulting in rearrangement of membrane structure. The goal of this study was to map the fusogenic and lytic domains of SP-B and assess the effects of altered fusion and lysis on surface activity. Synthetic peptides were generated to predicted helices and/or interhelical loops of SP-B and tested for fusion, lytic, and surface activities. The N-terminal half of SP-B (residues 1-37), which includes the nonhelical N-terminal amino acids in addition to helices 1 and 2, promoted rapid liposome fusion whereas shorter peptides were significantly less effective. The requirements for optimal surface tension reduction were similar to those for fusion; in contrast, helix 1 (residues 7-22) alone was sufficient for liposome lysis. The C-terminal half of SP-B (residues 43-79), which includes helices 3, 4, and 5, exhibited significantly lower levels of fusogenic, lytic, and surface tension reducing activities compared to the N-terminal region. These results indicate that SP-B fusion, lytic and surface activities map predominantly to the N-terminal half of SP-B. Amino acid substitutions in synthetic peptides corresponding to the N-terminal half of SP-B indicated that, in general, decreased fusion or lytic activities were associated with altered surface tension reducing properties of the peptide. However, the presence of fusion and lytic activities alone could not account for the surface tension reducing property of SP-B. We propose a model in which association of helix 1 with lipids leads to membrane permeabilization but not aggregation; helix 2 mediates membrane cross-linking (aggregation), which, in turn, facilitates lipid mixing, membrane fusion, and interfacial adsorption/surface tension reduction.