Vincent J S, Revak S D, Cochrane C D, Levin I W
Chemistry Department, University of Maryland Baltimore County, Catonsville 21228.
Biochemistry. 1993 Aug 17;32(32):8228-38. doi: 10.1021/bi00083a025.
The temperature dependence and acyl chain packing properties of the binary lipid mixtures of dipalmitoylphosphatidylcholine-d62 (DPPC-d62)/dipalmitoylphosphatidylglycerol (DPPG) multilayers, reconstituted with two synthetic peptides for modeling the membrane behavior of the SP-B protein associated with human pulmonary surfactant, were investigated by vibrational Raman spectroscopy. The synthetic peptides consisted of 21 amino acid residues representing repeating charged units of either lysine or aspartic acid separated by hydrophobic domains consisting of four leucines (KL4 or DL4, respectively). These peptides were designed to mimic the alternating hydrophobic and hydrophilic sequences defining the low molecular weight SP-B protein. Raman spectroscopic parameters consisting of integrated band intensities, line widths, and relative peak height intensity ratios were used to probe the bilayer order/disorder characteristics of the liposomal perturbations reflected by the reconstituted membrane assemblies. Temperature profiles derived from the various Raman intensity parameters for the 3100-2800-cm-1 carbon-hydrogen (C-H) and the 2000-2300-cm-1 carbon-deuterium (C-D) stretching mode regions, spectral intervals representative of acyl chain vibrations, reflected lipid reorganizations specific to peptide interactions with either the DPPC-d62 or DPPG component of the liposome. For the multilamellar surfactant systems composed of either KL4 or DL4 reconstituted with the binary DPPG/DPPC-d62 lipid mixture, the breadth of the gel to liquid crystalline phase transition temperatures TM, defined by acyl chain C-H and C-D stretching mode order/disorder parameters, increased from about 1 degree C in the peptide-free systems to over 10 degrees C. This breadth in TM indicates an increased lipid disorder and a distinct noncooperative chain melting process for the model liposomes. In comparing the interactions of the synthetic peptides with DPPG/DPPC mixtures and with DPPC liposomes alone, the negatively charged DL4 peptide perturbs the DPPG component of the lipid mixture more strongly than the DPPC-d62 component; moreover, the DL4 peptide disrupts the structure of the DPPG lipid domains in the binary mixture to a greater extent than the KL4 peptide. The microdomain heterogeneity of the binary lipid mixture arising from lipid-peptide interactions is discussed in terms of the Raman spectral properties of the multilayers. The Raman data in conjunction with previous bubble surfactometer and animal studies (Cochrane & Revak, 1991) suggest that lipid domain structures are present in functional surfactants and that the dynamic bilayer microheterogeneity induced by the surfactant peptide or protein is essential for pulmonary mechanics.
通过振动拉曼光谱研究了二棕榈酰磷脂酰胆碱 - d62（DPPC - d62）/二棕榈酰磷脂酰甘油（DPPG）多层膜的二元脂质混合物的温度依赖性和酰基链堆积性质，该混合物用两种合成肽进行了重构，用于模拟与人肺表面活性剂相关的SP - B蛋白的膜行为。合成肽由21个氨基酸残基组成，代表赖氨酸或天冬氨酸的重复带电单元，中间由四个亮氨酸组成的疏水结构域隔开（分别为KL4或DL4）。这些肽被设计用来模拟定义低分子量SP - B蛋白的交替疏水和亲水序列。由积分带强度、线宽和相对峰高强度比组成的拉曼光谱参数用于探测重构膜组装体所反映的脂质体扰动的双层有序/无序特征。从3100 - 2800 cm⁻¹碳 - 氢（C - H）和2000 - 2300 cm⁻¹碳 - 氘（C - D）伸缩模式区域的各种拉曼强度参数得出的温度曲线，这两个光谱区间代表酰基链振动，反映了肽与脂质体的DPPC - d62或DPPG组分相互作用时特定的脂质重组。对于由KL4或DL4与二元DPPG/DPPC - d62脂质混合物重构而成的多层表面活性剂体系，由酰基链C - H和C - D伸缩模式有序/无序参数定义的凝胶到液晶相转变温度TM的宽度，从无肽体系中的约1℃增加到超过10℃。TM的这种宽度表明模型脂质体的脂质无序增加和明显的非协同链熔化过程。在比较合成肽与DPPG/DPPC混合物以及单独与DPPC脂质体的相互作用时，带负电荷的DL4肽对脂质混合物的DPPG组分的扰动比对DPPC - d62组分更强；此外，DL4肽比KL4肽更大程度地破坏了二元混合物中DPPG脂质域的结构。根据多层膜的拉曼光谱性质讨论了由脂质 - 肽相互作用引起的二元脂质混合物的微区异质性。拉曼数据与先前的气泡表面张力仪和动物研究（Cochrane & Revak，1991）表明，脂质域结构存在于功能性表面活性剂中，并且表面活性剂肽或蛋白诱导的动态双层微异质性对于肺力学至关重要。
