Gerdes Lars, Bals Thomas, Klostermann Eva, Karl Monique, Philippar Katrin, Hünken Mark, Soll Jürgen, Schünemann Danja
Department für Biologie I, Botanik, Ludwig-Maximilians-Universität, 80638 München, Germany.
J Biol Chem. 2006 Jun 16;281(24):16632-42. doi: 10.1074/jbc.M513623200. Epub 2006 Apr 4.
The integral membrane proteins Alb3, OxaI, and YidC belong to an evolutionary conserved protein family mediating protein insertion into the thylakoid membrane of chloroplasts, the inner membrane of mitochondria, and bacteria, respectively. Whereas OxaI and YidC are involved in the insertion of a wide range of membrane proteins, the function of Alb3 seems to be limited to the insertion of a subset of the light-harvesting chlorophyll-binding proteins. In this study, we identified a second chloroplast homologue of the Alb3/OxaI/YidC family, named Alb4. Alb4 is almost identical to the Alb3/OxaI/YidC domain of the previously described 110-kDa inner envelope protein Artemis. We show that Alb4 is expressed as a separate 55-kDa protein and that Artemis was identified mistakenly. Alb4 is located in the thylakoid membrane of Arabidopsis thaliana chloroplasts. Analysis of an Arabidopsis mutant (Salk_136199) and RNA interference lines with a reduced level of Alb4 revealed chloroplasts with an altered ultrastructure. Mutant plastids are larger and more spherical in appearance, and the grana stacks within the mutant lines are less appressed than in the wild-type chloroplasts. These data indicate that Alb4 is required for proper chloroplast biogenesis.
整合膜蛋白Alb3、OxaI和YidC属于一个进化保守的蛋白家族，分别介导蛋白质插入叶绿体的类囊体膜、线粒体的内膜以及细菌中。虽然OxaI和YidC参与多种膜蛋白的插入，但Alb3的功能似乎仅限于插入一部分捕光叶绿素结合蛋白。在本研究中，我们鉴定出了Alb3/OxaI/YidC家族的第二个叶绿体同源物，命名为Alb4。Alb4与先前描述的110 kDa内膜蛋白Artemis的Alb3/OxaI/YidC结构域几乎相同。我们发现Alb4作为一种单独的55 kDa蛋白表达，并且Artemis是被错误鉴定的。Alb4位于拟南芥叶绿体的类囊体膜中。对拟南芥突变体（Salk_136199）和Alb4水平降低的RNA干扰株系进行分析，发现叶绿体的超微结构发生了改变。突变体质体在外观上更大且更呈球形，突变株系中的基粒堆叠比野生型叶绿体中的更松散。这些数据表明Alb4是叶绿体正常生物发生所必需的。
