Lei Xiaotong, Liu Shengtang, Zhou Ruhong, Meng Xuan-Yu
Institute of Quantitative Biology and Medicine, State Key Laboratory of Radiation Medicine and Protection, School of Radiation Medicine and Protection, Collaborative Innovation Center of Radiation Medicine of Jiangsu Higher Education Institutions, Soochow University, Suzhou 215123, China.
Department of Chemistry, Columbia University, New York, New York 10027, United States.
J Phys Chem B. 2021 Apr 15;125(14):3476-3485. doi: 10.1021/acs.jpcb.0c10513. Epub 2021 Mar 31.
Cyclotides are disulfide-rich cyclic peptides isolated from plants, which are extremely stable against thermal and proteolytic degradation, with a variety of biological activities including antibacterial, hemolytic, anti-HIV, and anti-tumor. Most of these bioactivities are related to their preference for binding to certain types of phospholipids and subsequently disrupt lipid membranes. In the present study, we use a cyclotide, cycloviolacin O2 (cyO2), as a model system to investigate its interactions with three lipid bilayers 1-palmitoyl-2-oleoylphosphatidylethanolamine (POPE), 1-palmitoyl-2-oleoyl--glycero-3-phosphoglycerol (POPG)-doped POPE, and 1-palmitoyl-2-oleoylphosphatidylcholine (POPC), to help understand its potential mechanism of action toward the membranes at the molecular level using molecular dynamics simulations. In our simulations, cyO2 repeatedly forms stable binding complexes with the POPE-containing bilayers, while within the same simulation time scale, it "jumps" back and forth on the surface of the POPC bilayer without a strong binding. Detailed analyses reveal that the electrostatic attraction is the main driving force for the initial bindings between cyO2 and the lipids, but with strikingly different strengths in different bilayers. For the POPE-containing bilayers, the charged residues of cyO2 attract both POPE amino and phosphate head groups favorably; meanwhile, its hydrophobic residues are deeply inserted into the lipid hydrophobic tails (core) of the membrane, thus forming stable binding complexes. In contrast, POPC lipids with three methyl groups on the amino head group create a steric hindrance when interacting with cyO2, thus resulting in a relatively difficult binding of cyO2 on POPC compared to POPE. Our current findings provide additional insights for a better understanding of how cyO2 binds to the POPE-containing membrane, which should shed light on the future cyclotide-based antibacterial agent design.
环肽是从植物中分离出来的富含二硫键的环肽，对热和蛋白水解降解具有极强的稳定性，具有多种生物活性，包括抗菌、溶血、抗HIV和抗肿瘤活性。这些生物活性大多与其优先结合某些类型的磷脂并随后破坏脂质膜有关。在本研究中，我们使用环肽环紫罗兰素O2（cyO2）作为模型系统，研究其与三种脂质双层的相互作用，即1-棕榈酰-2-油酰磷脂酰乙醇胺（POPE）、1-棕榈酰-2-油酰-甘油-3-磷酸甘油（POPG）掺杂的POPE以及1-棕榈酰-2-油酰磷脂酰胆碱（POPC），以通过分子动力学模拟在分子水平上帮助理解其对膜的潜在作用机制。在我们的模拟中，cyO2与含POPE的双层反复形成稳定的结合复合物，而在相同的模拟时间尺度内，它在POPC双层表面来回“跳跃”，没有强结合。详细分析表明，静电吸引是cyO2与脂质之间初始结合的主要驱动力，但在不同双层中的强度明显不同。对于含POPE的双层，cyO2的带电荷残基有利地吸引POPE的氨基和磷酸头部基团；同时，其疏水残基深深插入膜的脂质疏水尾部（核心），从而形成稳定的结合复合物。相比之下，氨基头部带有三个甲基的POPC脂质在与cyO2相互作用时会产生空间位阻，因此与POPE相比，cyO2在POPC上的结合相对困难。我们目前的研究结果为更好地理解cyO2如何与含POPE的膜结合提供了更多见解，这应该为未来基于环肽的抗菌剂设计提供启示。
