Department of Physiology and Pharmacology, Sackler Faculty of Medicine, Tel Aviv University, Tel Aviv, Israel.
Department of Physiology and Pharmacology, Sackler Faculty of Medicine, Tel Aviv University, Tel Aviv, Israel.
Biophys J. 2023 Jun 6;122(11):1974-1984. doi: 10.1016/j.bpj.2022.10.005. Epub 2022 Oct 5.
Tubular networks of the endoplasmic reticulum (ER) are dynamic structures whose steady-state conformations are maintained by a balance between the persistent generation and vanishing of the network elements. While factors producing the ER tubules and intertubular junctions have been investigated, the mechanisms behind their elimination remained unknown. Here, we addressed the ER ring closure, the process resulting in the tubule and junction removal through constriction of the network unit cells into junctional knots followed by the knot remodeling into regular junctions. We considered the ring closure to be driven by the tension existing in ER membranes. We based our consideration on the notion of Gibbs' thermodynamic tension and reviewed its relationship to other tension definitions used in the literature. We modeled, computationally, the structures of the junctional knots containing internal nanopores and analyzed their tension dependence. We analyzed the process of the pore sealing through membrane fission resulting in the formation of regular junctions. Considering the hemi-fission as the rate-limiting stage of the fission reaction, we evaluated the membrane tensions guaranteeing the spontaneous character of the pore sealing. We concluded that feasible membrane tensions explain all stages of the ER ring closure.
内质网（ER）的管状网络是动态结构，其稳定状态构象通过网络元件的持续产生和消失之间的平衡来维持。虽然已经研究了产生 ER 小管和管间连接的因素，但它们消除的机制仍然未知。在这里，我们研究了 ER 环闭合，即通过网络单元细胞在连接结处收缩，然后将结重塑成规则连接，从而导致小管和连接去除的过程。我们认为环闭合是由 ER 膜中的张力驱动的。我们基于 Gibbs 热力学张力的概念，并回顾了其与文献中使用的其他张力定义的关系。我们通过计算建模了含有内部纳米孔的连接结的结构，并分析了它们的张力依赖性。我们通过膜分裂导致形成规则连接来分析孔密封的过程。考虑到半裂变是裂变反应的限速阶段，我们评估了保证孔密封自发性的膜张力。我们得出结论，可行的膜张力可以解释 ER 环闭合的所有阶段。
