Calcium-dependent and -independent lipid transfer mediated by tricalbins in yeast.
Calcium-dependent and -independent lipid transfer mediated by tricalbins in yeast.
复制标题
酵母中三卡宾介导的钙依赖性和非依赖性脂质转移
DOI：
10.1016/j.jbc.2021.100729
复制
发表时间：
2021-01
期刊：
影响因子：
--
通讯作者：
Yu H
中科院分区：
文献类型：
--
作者：
Qian T;Li C;He R;Wan C;Liu Y;Yu H
在内质网(ER)和质膜(PM)之间形成的膜接触点(MCSs)为非囊泡性脂质交换提供了平台。内质网锚定的三碳联素(Tcb1、Tcb2和Tcb3)是酵母中ER-PM MCSs的关键锚定因子。Tricalbins具有突触素样脂结合蛋白(SMP)结构域和多个钙结合C2结构域。尽管已有研究表明三钙素参与ER-PM MCSs的脂类交换，但目前尚不清楚它们是否直接介导脂类转运。在这里，使用体外脂转移试验，我们发现三碳酸脂能够在膜之间转移磷脂。出乎意料的是，尽管Tcb3的脂质转移活性在钙离子的作用下显著增加，但即使在没有钙离子的情况下，Tcb3也会结构性地转移脂类。钙离子对Tcb3的刺激作用需要在Tcb3的C2c和C2d结构域上有完整的钙结合部位，而非钙依赖的脂质转运是由SMP结构域介导的，它通过直接与磷脂酰丝氨酸和其他带负电荷的脂分子相互作用来传递脂类。这些发现确立了三碳酸脂作为脂转移蛋白，并揭示了这些三碳酸脂介导的钙依赖和非依赖的脂转移活性，为它们在ER-PM MCSs维持PM完整性的机制提供了新的见解。
Membrane contact sites (MCSs) formed between the endoplasmic reticulum (ER) and the plasma membrane (PM) provide a platform for nonvesicular lipid exchange. The ER-anchored tricalbins (Tcb1, Tcb2, and Tcb3) are critical tethering factors at ER–PM MCSs in yeast. Tricalbins possess a synaptotagmin-like mitochondrial-lipid-binding protein (SMP) domain and multiple Ca2+-binding C2 domains. Although tricalbins have been suggested to be involved in lipid exchange at the ER–PM MCSs, it remains unclear whether they directly mediate lipid transport. Here, using in vitro lipid transfer assays, we discovered that tricalbins are capable of transferring phospholipids between membranes. Unexpectedly, while its lipid transfer activity was markedly elevated by Ca2+, Tcb3 constitutively transferred lipids even in the absence of Ca2+. The stimulatory activity of Ca2+ on Tcb3 required intact Ca2+-binding sites on both the C2C and C2D domains of Tcb3, while Ca2+-independent lipid transport was mediated by the SMP domain that transferred lipids via direct interactions with phosphatidylserine and other negatively charged lipid molecules. These findings establish tricalbins as lipid transfer proteins, and reveal Ca2+-dependent and -independent lipid transfer activities mediated by these tricalbins, providing new insights into their mechanism in maintaining PM integrity at ER–PM MCSs.