Three distinct kinetic groupings of the synaptotagmin family: Candidate sensors for rapid and delayed exocytosis
Three distinct kinetic groupings of the synaptotagmin family: Candidate sensors for rapid and delayed exocytosis
复制标题
DOI：
10.1073/pnas.0500941102
复制
发表时间：
2005-04-05
影响因子：
11.1
通讯作者：
Chapman, ER
中科院分区：
文献类型：
--
作者：
Hui, EF;Bai, JH;Chapman, ER
突触结合蛋白 (syts) 是存在于多种细胞内细胞器上的膜蛋白家族。在脊椎动物中，已鉴定出 16 种 syt 亚型。最丰富的亚型 syt 1 似乎起到 Ca2+ 传感器的作用，触发神经元突触小泡的快速胞吐作用。其余 syt 同工型的功能尚不清楚。 syt I 的胞质结构域响应 Ca2+ 与膜结合，并且这种相互作用已被认为在分泌中发挥关键作用。在这里，我们测试了 syts I-XII 细胞质结构域的 Ca2+ 触发的膜结合活性；八种异构体与含有磷脂酰丝氨酸的脂质体紧密结合。 Ca2+浓度的函数。然后，我们比较了与过量 Ca2+ 螯合剂快速混合后 Ca2+-syt-膜复合物的分解动力学，发现 syt 可分为三个不同的动力学组。 syts I、II、III 构成快速组； syts V、VI、IX 和 X 组成中组； syt VII 的分解动力学最慢。因此，syt 的异构体（其分解动力学比 syt 1 慢得多）可能充当异步释放的 Ca2+ 传感器，异步释放发生在 Ca2+ 结构域崩溃后。我们还使用鱿鱼和大鼠 syt I 比较了 Ca2+-syt 膜组装和拆卸反应的温度依赖性。这些结果表明 syt 已分化以不同的动力学释放 Ca2+ 和膜。
Synaptotagmins (syts) are a family of membrane proteins present on a variety of intracellular organelles. In vertebrates, 16 isoforms of syt have been identified. The most abundant isoform, syt 1, appears to function as a Ca2+ sensor that triggers the rapid exocytosis of synaptic vesicles from neurons. The functions of the remaining syt isoforms are less well understood. The cytoplasmic domain of syt I binds membranes in response to Ca2+, and this interaction has been proposed to play a key role in secretion. Here, we tested the Ca2+-triggered membrane-binding activity of the cytoplasmic domains of syts I-XII; eight isoforms tightly bound to liposomes that contained phosphatidylserine as. a function of the concentration of Ca2+. We then compared the disassembly kinetics of Ca2+-syt-membrane complexes upon rapid mixing with excess Ca2+ chelator and found that syts can be classified into three distinct kinetic groups. syts I, II, and III constitute the fast group; syts V, VI, IX, and X make up the medium group; and syt VII exhibits the slowest kinetics of disassembly. Thus, isoforms of syt, which have much slower disassembly kinetics than does syt 1, might function as Ca2+ sensors for asynchronous release, which occurs after Ca2+ domains have collapsed. We also compared the temperature dependence of Ca2+-syt-membrane assembly and disassembly reactions by using squid and rat syt I. These results indicate that syts have diverged to release Ca2+ and membranes with distinct kinetics.