Inaba Takehito, Li Ming, Alvarez-Huerta Mayte, Kessler Felix, Schnell Danny J
Department of Biochemistry and Molecular Biology, University of Massachusetts, Amherst, Massachusetts 01003, USA.
J Biol Chem. 2003 Oct 3;278(40):38617-27. doi: 10.1074/jbc.M306367200. Epub 2003 Jul 21.
The translocon of the inner envelope membrane of chloroplasts (Tic) mediates the late events in the translocation of nucleus-encoded preproteins into chloroplasts. Tic110 is a major integral membrane component of active Tic complexes and has been proposed to function as a docking site for translocation-associated stromal factors and as a component of the protein-conducting channel. To investigate the various proposed functions of Tic110, we have investigated the structure, topology, and activities of a 97.5-kDa fragment of Arabidopsis Tic110 (atTic110) lacking only the amino-terminal transmembrane segments. The protein was expressed both in Escherichia coli and Arabidopsis as a stable, soluble protein with a high alpha-helical content. Binding studies demonstrate that a region of the atTic110-soluble domain selectively associates with chloroplast preproteins at the late stages of membrane translocation. These data support the hypothesis that the bulk of Tic110 extends into the chloroplast stroma and suggest that the domain forms a docking site for preproteins as they emerge from the Tic translocon.
叶绿体内膜易位子（Tic）介导核编码前体蛋白转运至叶绿体的后期事件。Tic110是活性Tic复合物的主要整合膜成分，有人提出它作为转运相关基质因子的停靠位点以及蛋白质传导通道的组成部分发挥作用。为了研究Tic110的各种假定功能，我们研究了拟南芥Tic110（atTic110）仅缺少氨基末端跨膜片段的97.5 kDa片段的结构、拓扑结构和活性。该蛋白在大肠杆菌和拟南芥中均作为具有高α-螺旋含量的稳定可溶性蛋白表达。结合研究表明，atTic110可溶性结构域的一个区域在膜转运后期与叶绿体前体蛋白选择性结合。这些数据支持了Tic110大部分延伸到叶绿体基质中的假设，并表明该结构域在预蛋白从Tic易位子出现时形成了一个停靠位点。
