Gonzalez-Horta Azucena, Andreu David, Morrow Michael R, Perez-Gil Jesús
Departamento de Bioquímica y Biología Molecular, Facultad de Biología, Universidad Complutense, Madrid, Spain.
Biophys J. 2008 Sep;95(5):2308-17. doi: 10.1529/biophysj.108.132845. Epub 2008 May 23.
It has been proposed that palmitoylation of the N-terminal segment of surfactant protein SP-C is important for maintaining association of pulmonary surfactant complexes with interfacial films compressed to high pressures at the end of expiration. In this study, we examined surfactant membrane models containing palmitoylated and nonpalmitoylated synthetic peptides, based on the N-terminal SP-C sequence, in dipalmitoylphosphatidylcholine (DPPC)/egg phosphatidylglycerol (7:3, w/w) by (2)H-NMR. Perturbations of lipid properties by the peptide versions were compared in samples containing chain- and headgroup-deuterated lipid (DPPC-d(62) and DPPC-d(4) respectively). Also, deuterated peptide palmitate chains were compared with those of DPPC in otherwise identical lipid-protein mixtures. Palmitoylated peptide increased average DPPC-d(62) chain orientational order slightly, particularly for temperatures spanning gel and liquid crystalline coexistence, implying penetration of palmitoylated peptide into ordered membrane. In contrast, the nonpalmitoylated peptide had a small disordering effect in this temperature range. Both peptide versions perturbed DPPC-d(4) headgroup orientation similarly, suggesting little effect of palmitoylation on the largely electrostatic peptide-headgroup interaction. Deuterated acyl chains attached to the SP-C N-terminal segment displayed a qualitatively different distribution of chain order, and lower average order, than DPPC-d(62) in the same membranes. This likely reflects local perturbation of lipid headgroup spacing by the peptide portion interacting with the bilayer near the peptide palmitate chains. This study suggests that SP-C-attached acyl chains could be important for coupling of lipid and protein motions in surfactant bilayers and monolayers, especially in the context of ordered phospholipid structures such as those potentially formed during exhalation, when stabilization of the respiratory surface by surfactant is the most crucial.
有人提出，表面活性蛋白SP-C N端片段的棕榈酰化对于维持肺表面活性物质复合物与呼气末期压缩至高压的界面膜的结合很重要。在本研究中，我们通过（2）H-NMR研究了基于SP-C N端序列的含有棕榈酰化和非棕榈酰化合成肽的表面活性膜模型，该模型存在于二棕榈酰磷脂酰胆碱（DPPC）/鸡蛋磷脂酰甘油（7:3，w/w）中。在含有链氘代和头基团氘代脂质（分别为DPPC-d(62)和DPPC-d(4)）的样品中，比较了肽变体对脂质性质的扰动。此外，在其他条件相同的脂质-蛋白质混合物中，将氘代肽棕榈酸链与DPPC的进行了比较。棕榈酰化肽略微增加了平均DPPC-d(62)链的取向有序度，特别是在跨越凝胶和液晶共存的温度范围内，这意味着棕榈酰化肽渗透到有序膜中。相比之下，非棕榈酰化肽在该温度范围内具有较小的无序化作用。两种肽变体对DPPC-d(4)头基团取向的扰动相似，表明棕榈酰化对主要为静电作用的肽-头基团相互作用影响很小。与同一膜中的DPPC-d(62)相比，连接到SP-C N端片段的氘代酰基链显示出链有序度的定性不同分布，且平均有序度较低。这可能反映了肽部分与肽棕榈酸链附近的双层相互作用对脂质头基团间距的局部扰动。这项研究表明，与SP-C相连的酰基链对于表面活性双层和单层中脂质和蛋白质运动的耦合可能很重要，特别是在有序磷脂结构的情况下，例如呼气过程中可能形成的结构，此时表面活性物质对呼吸表面的稳定最为关键。
