CIQUP, Centro de Investigação em Química, Departamento de Química e Bioquímica, Faculdade de Ciências, Universidade do Porto, Porto, Portugal.
Centro Singular de Investigación en Química Biolóxica e Materiais Moleculares (CiQUS), Departamento de Química Orgánica, Universidade de Santiago de Compostela, 15782 Santiago de Compostela, Spain.
Colloids Surf B Biointerfaces. 2020 Dec;196:111349. doi: 10.1016/j.colsurfb.2020.111349. Epub 2020 Sep 9.
The search of new antibiotics, particularly with new mechanisms of action, is nowadays a very important public health issue, due to the worldwide increase of resistant pathogens. Within this effort, much research has been done on antimicrobial peptides, because having the membrane as a target, they represent a new antibiotic paradigm. Among these, cyclic peptides (CPs) made of sequences of D- and L-amino acids have emerged as a new class of potential antimicrobial peptides, due to their expected higher resistance to protease degradation. These CPs are planar structures that can form Self-assembled Cyclic Peptide Nanotubes (SCPNs), in particular in the presence of lipid membranes. Aiming at understanding their mechanism of action, we used biophysical experimental techniques (DSC and ATR-FTIR) together with Coarse-grained molecular dynamics (CG-MD) simulations, to characterize the interaction of these CPs with model membranes of different electrostatic charges' contents. DSC results revealed that the CPs show a strong interaction with negatively charged membranes, with differences in the strength of interactions depending on peptide and on membrane charge content, at odds with no or mild interactions with zwitterionic membranes. ATR-FTIR suggested that the peptides self-assemble at the membrane surface, adopting mainly a β-structure. The experiments with polarized light showed that in most cases they lie parallel to the membrane surface, but other forms and orientations are also apparent, depending on peptide structure and lipid:peptide ratio. The nanotube formation and orientation, as well as the dependence on membrane charge were also confirmed by the CG-MD simulations. These provide detail on the position and interactions, in agreement with the experimental results. Based on the findings reported here, we could proceed to the design and synthesis of a second-generation CPs, based on CP2 (soluble peptide), with increased activity and reduced toxicity.
寻找新的抗生素，尤其是具有新作用机制的抗生素，是当今一个非常重要的公共卫生问题，因为全球范围内耐药病原体的数量不断增加。在这一努力中，人们对抗菌肽进行了大量研究，因为作为一种新的抗生素模式，抗菌肽以膜为靶标。在这些抗菌肽中，由 D-和 L-氨基酸序列组成的环状肽 (CP) 已成为一类新的潜在抗菌肽，因为它们预计对蛋白酶降解的抗性更高。这些 CP 是平面结构，可以在存在脂质膜的情况下形成自组装环状肽纳米管 (SCPN)。为了了解它们的作用机制，我们使用生物物理实验技术（DSC 和 ATR-FTIR）以及粗粒度分子动力学 (CG-MD) 模拟，来表征这些 CP 与不同静电荷含量的模型膜的相互作用。DSC 结果表明，CP 与带负电荷的膜具有强烈的相互作用，其相互作用强度取决于肽和膜电荷含量的差异，与与两性离子膜之间没有或只有轻微的相互作用形成对比。ATR-FTIR 表明，肽在膜表面自组装，主要采用β-结构。偏振光实验表明，在大多数情况下，它们与膜表面平行，但也存在其他形式和取向，这取决于肽结构和脂质：肽比。CG-MD 模拟还证实了纳米管的形成和取向以及对膜电荷的依赖性。这些模拟提供了与实验结果一致的位置和相互作用的细节。基于这里报道的发现，我们可以着手设计和合成第二代 CP2（可溶性肽）的 CP，提高其活性并降低其毒性。
