Federizon Jasmin, Feugmo Conrard Giresse Tetsassi, Huang Wei-Chiao, He Xuedan, Miura Kazutoyo, Razi Aida, Ortega Joaquin, Karttunen Mikko, Lovell Jonathan F
Department of Biomedical Engineering, University at Buffalo, State University of New York, Buffalo, NY 14260, USA.
Department of Chemistry, the University of Western Ontario, London, ON N6A 3K7, Canada.
Pharmaceutics. 2021 Jan 14;13(1):98. doi: 10.3390/pharmaceutics13010098.
Cobalt porphyrin phospholipid (CoPoP) can incorporate within bilayers to enable non-covalent surface-display of antigens on liposomes by mixing with proteins bearing a polyhistidine tag (his-tag); however, the mechanisms for how this occurs are poorly understood. These were investigated using the his-tagged model antigen Pfs25, a protein antigen candidate for malaria transmission-blocking vaccines. Pfs25 was found to associate with the small molecule aquocobalamin, a form of vitamin B12 and a cobalt-containing corrin macrocycle, but without particle formation, enabling comparative assessment. Relative to CoPoP liposomes, binding and serum stability studies indicated a weaker association of Pfs25 to aquocobalamin or cobalt nitrilotriacetic acid (Co-NTA) liposomes, which have cobalt displayed in the aqueous phase on lipid headgroups. Antigen internalization by macrophages was enhanced with Pfs25 bound to CoPoP liposomes. Immunization in mice with Pfs25 bound to CoPoP liposomes elicited antibodies that recognized ookinetes and showed transmission-reducing activity. To explore the physical mechanisms involved, we employed molecular dynamics (MD) simulations of bilayers containing phospholipid, cholesterol, as well as either CoPoP or NTA-functionalized lipids. The results show that the CoPoP-containing bilayer creates nanodomains that allow access for a limited but sufficient amount of water molecules that could be replaced by his-tags due to their favorable free energy properties allowing for stabilization. The position of the metal center within the NTA liposomes was much more exposed to the aqueous environment, which could explain its limited capacity for stabilizing Pfs25. This study illustrates the impact of CoPoP-induced antigen particleization in enhancing vaccine efficacy, and provides molecular insights into the CoPoP bilayer properties that enable this.
钴卟啉磷脂（CoPoP）可以整合到双层膜中，通过与带有多组氨酸标签（his-tag）的蛋白质混合，实现抗原在脂质体上的非共价表面展示；然而，其发生机制尚不清楚。使用带有his-tag的模型抗原Pfs25（一种疟疾传播阻断疫苗的蛋白质抗原候选物）对此进行了研究。发现Pfs25与小分子水合钴胺素（维生素B12的一种形式，含钴的咕啉大环化合物）相关联，但未形成颗粒，从而能够进行比较评估。相对于CoPoP脂质体，结合和血清稳定性研究表明，Pfs25与水合钴胺素或次氮基三乙酸钴（Co-NTA）脂质体的结合较弱，后者的钴展示在脂质头部基团的水相中。巨噬细胞对Pfs25结合的CoPoP脂质体的抗原内化作用增强。用Pfs25结合的CoPoP脂质体免疫小鼠可引发识别动合子并具有传播减少活性的抗体。为了探索其中涉及的物理机制，我们对含有磷脂、胆固醇以及CoPoP或NTA功能化脂质的双层膜进行了分子动力学（MD）模拟。结果表明，含CoPoP的双层膜形成了纳米域，允许有限但足够数量的水分子进入，这些水分子可被his-tag取代，因为它们具有有利的自由能特性，能够实现稳定。NTA脂质体中金属中心的位置更暴露于水环境中，这可以解释其稳定Pfs25的能力有限。这项研究说明了CoPoP诱导的抗原颗粒化对提高疫苗效力的影响，并提供了关于实现这一作用的CoPoP双层膜特性的分子见解。
