Institute of Molecular Biology, Academia Sinica, Taipei, 11529, Taiwan.
Plant J. 2013 Sep;75(5):847-57. doi: 10.1111/tpj.12249. Epub 2013 Jun 21.
Tic110 is a major component of the chloroplast protein import translocon. Two functions with mutually exclusive structures have been proposed for Tic110: a protein-conducting channel with six transmembrane domains and a scaffold with two N-terminal transmembrane domains followed by a large soluble domain for binding transit peptides and other stromal translocon components. To investigate the structure of Tic110, Tic110 from Cyanidioschyzon merolae (CmTic110) was characterized. We constructed three fragments, CmTic110A , CmTic110B and CmTic110C , with increasing N-terminal truncations, to perform small-angle X-ray scattering (SAXS) and X-ray crystallography analyses and Dali structural comparison. Here we report the molecular envelope of CmTic110B and CmTic110C determined by SAXS, and the crystal structure of CmTic110C at 4.2 Å. Our data indicate that the C-terminal half of CmTic110 possesses a rod-shaped helix-repeat structure that is too flattened and elongated to be a channel. The structure is most similar to the HEAT-repeat motif that functions as scaffolds for protein-protein interactions.
Tic110 是叶绿体蛋白输入转运体的主要组成部分。Tic110 具有两种结构互斥的功能：具有六个跨膜结构域的蛋白导通道和具有两个 N 端跨膜结构域的支架，其后是用于结合易位肽和其他基质转运体成分的大可溶性结构域。为了研究 Tic110 的结构，对来自 Cyanidioschyzon merolae（CmTic110）的 Tic110 进行了表征。我们构建了三个片段，CmTic110A、CmTic110B 和 CmTic110C，它们具有逐渐增加的 N 端截断，以进行小角度 X 射线散射（SAXS）和 X 射线晶体学分析以及 Dali 结构比较。在这里，我们报告了通过 SAXS 确定的 CmTic110B 和 CmTic110C 的分子包络，以及 CmTic110C 的晶体结构在 4.2Å。我们的数据表明，CmTic110 的 C 端半部分具有棒状螺旋重复结构，其扁平化和拉长程度使其无法成为通道。该结构与作为蛋白-蛋白相互作用支架的 HEAT-repeat 基序最为相似。
