Key Laboratory of Applied Marine Biotechnology of Ministry of Education, Ningbo University, Ningbo, Zhejiang 315211, PR China; School of Marine Sciences, Ningbo University, Ningbo, Zhejiang 315211, PR China; Hefei National Laboratory for Physical Sciences at Microscale and School of Life Sciences, University of Science and Technology of China, Hefei, Anhui 230026, PR China; Key Laboratory of Structural Biology, Chinese Academy of Sciences, Hefei, Anhui 230026, PR China.
Key Laboratory of Applied Marine Biotechnology of Ministry of Education, Ningbo University, Ningbo, Zhejiang 315211, PR China; School of Marine Sciences, Ningbo University, Ningbo, Zhejiang 315211, PR China.
Int J Biol Macromol. 2017 Feb;95:946-953. doi: 10.1016/j.ijbiomac.2016.10.083. Epub 2016 Oct 25.
Synaptotagmins constitute a family of multifunctional integral membrane proteins found predominantly on vesicles in neural and endocrine tissues. 17 isoforms of synaptotagmin family in mammals have been identified, 7 isoforms among them are known to be able to bind Ca via their C2 domains. This study presents the crystal structure of the first C2 domain (C2A domain) of synaptotagmin 5 complexed with Ca at 1.90Å resolution. Comparison of the Ca-binding pocket of synaptotagmin 5 C2A domain with other synaptotagmin C2 domains demonstrated that a serine residue locating at Ca-binding loop probably responsible to the conformational variation of Ca-binding pocket, and thus impacts the Ca-binding mechanism of C2 domain, which is verified by structural analysis of the serine mutant and Ca-binding assays via isothermal titration calorimetry. Alteration of Ca-binding mechanism might be correlated with different Ca response rates of synaptotagmins, which is the basis of the functions of synaptotagmins in regulating various types of Ca-triggered vesicle-membrane fusion processes.
突触结合蛋白构成了一个多功能的整合膜蛋白家族，主要存在于神经和内分泌组织的囊泡中。哺乳动物中已经鉴定出 17 种突触结合蛋白家族的同工型，其中 7 种同工型已知能够通过其 C2 结构域结合 Ca。本研究以 1.90Å 的分辨率呈现了突触结合蛋白 5 的第一个 C2 结构域（C2A 结构域）与 Ca 复合物的晶体结构。将突触结合蛋白 5 C2A 结构域的 Ca 结合口袋与其他突触结合蛋白 C2 结构域进行比较表明，位于 Ca 结合环上的一个丝氨酸残基可能负责 Ca 结合口袋构象的变化，从而影响 C2 结构域的 Ca 结合机制，这通过丝氨酸突变体的结构分析和等温滴定量热法的 Ca 结合实验得到了验证。Ca 结合机制的改变可能与突触结合蛋白不同的 Ca 反应速率有关，这是突触结合蛋白在调节各种类型的 Ca 触发的囊泡-膜融合过程中的功能基础。
