Engineering Fusogenic properties of lipid bilayers

描述（由申请方提供）：拟定研究的长期目标是为基于脂质体的药物递送载体的工程设计开发定量基础。脂质体作为诊断和治疗剂的递送载体具有显著的潜力。对于许多应用，脂质体作为递送载体的功效取决于其与靶膜隔室融合的能力。因此，控制和工程化脂质体双层的融合性的能力对于基于脂质体的递送载体的设计和制造是至关重要的。然而，目前对融合机制的理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，包括建模，高性能仿真和实验测量来解决这个问题。我们已经组建了一个小组，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，使用粗粒度（介观）模型的脂质双层，以处理必要的大型系统和长时间，同时保留系统的基本化学细节。参数化的粗粒度模型的脂质将确定匹配测量的数量，如弯曲模量和粗粒度的结构和能量的数量计算在所有原子分子动力学模拟。聚变将从假设的中间体开始模拟，以及使用弱导向力来激励该过程。这些模拟的结果将揭示融合动力学的分子细节，这将用于设计具有可预测的融合特性的脂质。然后将在基于脂质体的内容物混合测定中测试这些脂质，例如Tb/DPA系统。例如，初步模拟表明，通过在C（2）或C（3）位置引入大体积基团来限制甘油磷脂的甘油主链中C（2）至C（3）键的旋转，将降低脂质参与融合的能力。类似地，C（2）和C（3）位置之间的双键或环结构也会降低融合性。实验结果将用于进一步的模拟，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额外的实验方法进行重要的额外研究奠定基础。最后，这一努力的结果将为双层融合提供新的机理见解，并最终允许设计和工程化具有可预测的融合特性的脂质体。这反过来将大大推进脂质体作为药物递送载体的效用，并为涉及融合的生物过程提供重要见解。

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.