Shemyakin-Ovchinnikov Institute of Bioorganic Chemistry, Russian Academy of Sciences, Moscow, 117997, Russia.
Biochemistry (Mosc). 2014 May;79(5):459-68. doi: 10.1134/S0006297914050101.
Polysialic acid (PSA) is a natural anionic polymer typically occurring on the outer surface of cell membranes. PSA is involved in cell signaling and intermolecular interactions with proteins and peptides. The antimicrobial potential of peptides is usually evaluated in model membranes consisting of lipid bilayers but devoid of either PSA or its analogs. The goal of this work was to investigate the possible effect of PSA on the structure of melittin (Mlt) and latarcins Ltc1K, Ltc2a, and the activity of these peptides with respect to model membranes. These peptides are linear cationic ones derived from the venom of bee (Mlt) and spider (both latarcins). The length of each of the peptides is 26 amino acid residues, and they all have antimicrobial activity. However, they differ with respect to conformational mobility, hydrophobic characteristics, and overall charge. In this work, using circular dichroism spectroscopy, we show that the peptides adopt an α-helical conformation upon interaction with either PSA or phospholipid liposomes formed of either zwitterionic or anionic phospholipids or their mixtures. The extent of helicity depends on the amino acid sequence and properties of the medium. Based on small angle X-ray scattering data and the analysis of the fluorescence spectrum of the Trp residue in Mlt, we conclude that the peptide forms an oligomeric complex consisting of α-helical Mlt and several PSA molecules. Both latarcins, unlike Mlt, the most hydrophobic of the peptides, interact weakly with zwitterionic liposomes. However, they bind anionic liposomes or those composed of anionic/zwitterionic lipid mixtures. Latarcin Ltc1K forms associates on liposomes composed of zwitterionic/anionic lipid mixture. The structure of the peptide associates is either disordered or of β-sheet conformation. In all other cases the studied peptides adopt predominately α-helical conformation. In addition, we demonstrate that PSA inhibits membranolytic activity of Mlt and latarcin Ltc1K. These data suggest that the peptides, due to their high conformational lability, can vary structural and amphiphilic properties in the presence of PSA. As a result, various scenarios of the interaction of the peptides with membranes, whose surface is abundant with anionic polysaccharides, can take place. This can account for difficulties in understanding the structure-functional relationships in interactions of linear cationic peptides with biological membranes.
唾液酸聚糖 (PSA) 是一种天然的阴离子聚合物，通常存在于细胞膜的外表面。PSA 参与细胞信号传递以及与蛋白质和肽的分子间相互作用。肽的抗菌潜力通常在由脂质双层组成但缺乏 PSA 或其类似物的模型膜中进行评估。本工作的目的是研究 PSA 对蜂毒蜂肽 (Mlt) 和 latarcins Ltc1K、Ltc2a 的结构以及这些肽对模型膜的活性的可能影响。这些肽是源自蜜蜂 (Mlt) 和蜘蛛 (均为 latarcins) 毒液的线性阳离子肽。每个肽的长度为 26 个氨基酸残基，均具有抗菌活性。然而，它们在构象迁移性、疏水性特征和整体电荷方面有所不同。在这项工作中，我们使用圆二色性光谱表明，这些肽在与 PSA 或由两性离子或阴离子磷脂或其混合物形成的磷脂脂质体相互作用时采用 α-螺旋构象。螺旋度的程度取决于氨基酸序列和介质的性质。基于小角 X 射线散射数据和 Mlt 中色氨酸残基荧光光谱的分析，我们得出结论，该肽形成由 α-螺旋 Mlt 和几个 PSA 分子组成的寡聚复合物。与最疏水的肽 Mlt 不同，两种 latarcins 与两性离子脂质体的相互作用较弱。然而，它们与阴离子脂质体或由阴离子/两性离子脂质混合物组成的脂质体结合。Latarcin Ltc1K 与由两性离子/阴离子脂质混合物组成的脂质体形成复合物。肽结合物的结构要么无序，要么呈 β-折叠构象。在所有其他情况下，研究的肽均采用主要的 α-螺旋构象。此外，我们证明 PSA 抑制 Mlt 和 latarcin Ltc1K 的膜溶活性。这些数据表明，由于其高度构象灵活性，肽在 PSA 存在下可以改变结构和两亲性特性。因此，由于其表面富含阴离子多糖，各种肽与膜相互作用的情况都可能发生。这可以解释理解线性阳离子肽与生物膜相互作用的结构-功能关系的困难。
