Beijing Key Laboratory of Bioprocess, College of Life Science and Technology, Beijing University of Chemical Technology, Beijing, China.
Key Laboratory of Molecular Biophysics, Hebei Province, Institute of Biophysics, School of Science, Hebei University of Technology, Tianjin, China.
PLoS Comput Biol. 2020 Apr 9;16(4):e1007777. doi: 10.1371/journal.pcbi.1007777. eCollection 2020 Apr.
The co-localization of Cluster-of-Differentiation-44 protein (CD44) and cytoplasmic adaptors in specific membrane environments is crucial for cell adhesion and migration. The process is controlled by two different pathways: On the one hand palmitoylation keeps CD44 in lipid raft domains and disables the linking to the cytoplasmic adaptor, whereas on the other hand, the presence of phosphatidylinositol-4,5-biphosphate (PIP2) lipids accelerates the formation of the CD44-adaptor complex. The molecular mechanism explaining how CD44 is migrating into and out of the lipid raft domains and its dependence on both palmitoylations and the presence of PIP2 remains, however, elusive. In this study, we performed extensive molecular dynamics simulations to study the raft affinity and translocation of CD44 in phase separated model membranes as well as more realistic plasma membrane environments. We observe a delicate balance between the influence of the palmitoylations and the presence of PIP2 lipids: whereas the palmitoylations of CD44 increases the affinity for raft domains, PIP2 lipids have the opposite effect. Additionally, we studied the association between CD44 and the membrane adaptor FERM in dependence of these factors. We find that the presence of PIP2 lipids allows CD44 and FERM to associate in an experimentally observed binding mode whereas the highly palmitoylated species shows no binding affinity. Together, our results shed light on the sophisticated mechanism on how membrane translocation and peripheral protein association can be controlled by both protein modifications and membrane composition.
CD44 蛋白(CD44)和细胞质衔接蛋白在特定膜环境中的共定位对于细胞黏附和迁移至关重要。这个过程受两条不同的途径控制:一方面,棕榈酰化使 CD44 保持在脂筏结构域中,并阻止与细胞质衔接蛋白的连接,而另一方面,磷酸肌醇-4,5-二磷酸(PIP2)脂质的存在加速了 CD44-衔接蛋白复合物的形成。然而,解释 CD44 如何进出脂筏结构域及其对棕榈酰化和 PIP2 存在的依赖性的分子机制仍然难以捉摸。在这项研究中,我们进行了广泛的分子动力学模拟,以研究相分离模型膜中和更现实的质膜环境中 CD44 的筏亲和力和易位。我们观察到 CD44 的棕榈酰化和 PIP2 脂质的存在之间存在微妙的平衡:尽管 CD44 的棕榈酰化增加了对筏结构域的亲和力,但 PIP2 脂质则有相反的效果。此外,我们研究了这些因素对 CD44 与膜衔接蛋白 FERM 之间的关联的影响。我们发现,PIP2 脂质的存在允许 CD44 和 FERM 以实验观察到的结合模式结合,而高度棕榈酰化的物质则没有结合亲和力。总之,我们的研究结果揭示了膜易位和外周蛋白结合如何受蛋白质修饰和膜组成双重控制的复杂机制。