Cell surface calreticulin (CRT) can mediate apoptotic cells removal by binding and activating LDL receptor-related protein (LRP1). Phosphatidylserine (PS) lipids in the inner leaflet of the cell membrane are externalized and become exposed in cholesterol (CHOL)-rich membrane raft-like microdomain during apoptosis and co-localized with cell surface CRT. How the apoptotic raft-like membrane microdomain affects the structure and dynamics of CRT, further affecting CRT binding with LRP1 to signal apoptotic-cell clearance, remains unknown. In this study, we investigate the interactions between CRT and raft-like bilayers with or without POPS lipids with molecular dynamics simulations. In addition, the effect of an apoptotic raft bilayer on the binding between CRT and thrombospondin-1 (TSP1), a ligand of CRT on the cell surface to signal focal adhesion disassembly, was also investigated. Results of single CRT interactions with raft-like bilayers show that PS lipids in apoptotic raft-like bilayer increased the interactions between CRT and lipid bilayer, which enhanced the conformational stability and increased dynamical motion of CRT. The microscopic and mesoscopic properties of apoptotic raft-like bilayer were altered by the binding of CRT with lipid bilayer. Results of CRT-TSP1 complex interactions with raft-like bilayers show that the binding free energy between TSP1 and CRT was reduced in apoptotic raft-like bilayer environment. This study provides molecular and structural insight into the effect of an apoptotic raft-like bilayer on the conformation and dynamics of CRT, which could enrich our understanding of CRT-mediated apoptotic-cell clearance and focal adhesion disassembly.

中文翻译：

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对凋亡筏状双层对钙网蛋白构象和动力学的影响的分子见解。

细胞表面钙网蛋白（CRT）可以通过结合和激活LDL受体相关蛋白（LRP1）介导凋亡细胞的去除。细胞膜内小叶中的磷脂酰丝氨酸（PS）脂质被外化并在细胞凋亡过程中暴露于富含胆固醇（CHOL）的膜筏样微区中，并与细胞表面CRT共定位。凋亡筏状膜微结构域如何影响CRT的结构和动力学，进一步影响CRT与LRP1的结合以发出凋亡细胞清除的信号仍然未知。在这项研究中，我们用分子动力学模拟研究了CRT和筏状双层之间有或没有POPS脂质的相互作用。此外，凋亡筏双层对CRT和血小板反应蛋白1（TSP1）之间结合的影响，还研究了细胞表面上CRT的配体以发出粘着斑信号。单个CRT与筏状双层的相互作用的结果表明，凋亡的筏状双层中的PS脂质增加了CRT与脂质双层之间的相互作用，从而增强了CRT的构象稳定性和动态运动。CRT与脂质双层的结合改变了凋亡筏状双层的微观和介观性质。CRT-TSP1与筏状双层的复杂相互作用的结果表明，在凋亡的筏状双层环境中，TSP1和CRT之间的结合自由能降低。这项研究提供了分子和结构的洞察力，研究了凋亡的筏状双层对CRT的构象和动力学的影响，