Engineering Fusogenic properties of lipid bilayers

描述(由申请人提供)：拟议研究的长期目标是为基于脂质体的药物输送载体的工程设计开发一个量化基础。脂质体作为诊断和治疗药物的载体具有很大的潜力。对于许多应用，脂质体作为输送载体的有效性取决于其与靶膜隔室融合的能力。因此，控制和设计脂质体双层的融合性对于脂质体载体的设计和制造是至关重要的。然而，目前对融合机制的了解不足以达到这一目的。我们建议通过使用集成和跨学科的系统方法来解决这个问题，该方法包括建模、高性能模拟和实验测量。我们组建了一个小组，其中包括解决这一困难和复杂问题所需的专门知识。融合的模拟将在高度并行的计算机上进行，使用脂质双层的粗粒度(介观)模型，以便处理必要的大系统和长时间，同时保留系统的基本化学细节。粗粒脂质模型的参数将通过匹配测量的量，如弯曲模数，以及在所有原子分子动力学模拟中计算的粗粒结构和能量量来确定。聚变将从假想的中间体开始进行模拟，并使用弱转向力来推动这一过程。这些模拟的结果将揭示融合动力学的分子细节，这将被用于设计具有可预测的融合特性的脂质。这些脂类随后将在基于脂质体的内容混合分析中进行测试，例如TB/DPA系统。例如，初步模拟表明，通过在C(2)或C(3)位置引入大量基团来限制甘油磷脂甘油主链上C(2)到C(3)键的旋转，将降低脂质参与融合的能力。同样，C(2)和C(3)位置之间的双键或环结构也会降低融合性。实验结果将被用来为进一步的模拟提供信息，产生一个实验和模拟之间互动的过程。该项目的结果将为使用更复杂的模拟和更多的实验方法进行重大的额外研究奠定基础。最终，这一努力的结果将为双层融合提供新的机制洞察力，并最终允许设计和工程具有可预测的融合特性的脂质体。这反过来将显著提高脂质体作为药物输送载体的用途，并为涉及融合的生物过程贡献重要的见解。

DESCRIPTION (provided by applicant): The long-term objective of the proposed research is to develop a quantitative basis for the engineering of liposome based drug delivery vehicles. Liposomes have significant potential as delivery vehicles for diagnostic and therapeutic agents. For many applications, the efficacy of the liposome as a delivery vehicle depends on its ability to fuse with a target membrane compartment. Thus the ability to control and engineer the fusogenicity of the liposome bilayer is critical to the design and fabrication of liposome based delivery vehicles. However, current understanding of the mechanisms of fusion is inadequate for this purpose. We propose to address this problem by using an integrated and interdisciplinary systems approach that includes modeling, high performance simulation and experimental measurements. We have assembled a group that includes the expertise necessary to address this difficult and complex problem. Simulations of fusion will be performed on highly parallel computers using coarse-grained (mesoscopic) models for lipid bilayers in order to treat the necessary large systems and long times, while retaining the essential chemical detail of the system. Parameterization of the coarse-grained models of lipids will be determined by matching measured quantities such as bending moduli and by coarse-graining structural and energetic quantities calculated in all atom molecular dynamics simulations. Fusion will be simulated starting from hypothetical intermediates, as well as using a weak steering force to motivate the process. Results from these simulations will reveal molecular detail of fusion dynamics, which will be used to design lipids that have predictable fusogenic properties. These lipids will then be tested in liposome based content mixing assays, such as the Tb/DPA system. For example, preliminary simulations suggest that constraining the rotation of C(2) to C(3) bond in the glycerol backbone of a glycerophospholipid, by introducing a bulky group at the C(2) or C(3) position, will reduce the ability of the lipid to participate in fusion. Similarly, a double bond or ring structure between the C(2) and C(3) positions would also reduce fusogenicity. Results from experiments will be used to inform further simulations, producing a process that is interactive between experiment and simulation. Results from the project will lay the foundation for significant additional research using even more sophisticated simulations, and additional experimental methods. In the end, the result of this effort will provide new mechanistic insight into bilayer fusion and ultimately allow the design and engineering of liposomes with predictable fusogenic properties. That in turn will significantly advance the utility of liposomes as drug delivery vehicles, and contribute important insights to biological processes where fusion is involved.