Department of Mitochondrial Biology, Max Planck Institute for Biology of Ageing, Cologne, Germany.
Proc Natl Acad Sci U S A. 2012 Sep 18;109(38):15253-8. doi: 10.1073/pnas.1210688109. Epub 2012 Sep 4.
Proteins crucial for the respiratory chain are translated by the mitochondrial ribosome. Mitochondrial ribosome biogenesis is therefore critical for oxidative phosphorylation capacity and disturbances are known to cause human disease. This complex process is evolutionary conserved and involves several RNA processing and modification steps required for correct ribosomal RNA maturation. We recently showed that a member of the mitochondrial transcription termination factor (MTERF) family of proteins, MTERF4, recruits NSUN4, a 5-methylcytosine RNA methyltransferase, to the large ribosomal subunit in a process crucial for mitochondrial ribosome biogenesis. Here, we describe the 3D crystal structure of the human MTERF4-NSUN4 complex determined to 2.9 Å resolution. MTERF4 is composed of structurally repeated MTERF-motifs that form a nucleic acid binding domain. NSUN4 lacks an N- or C-terminal extension that is commonly used for RNA recognition by related RNA methyltransferases. Instead, NSUN4 binds to the C-terminus of MTERF4. A positively charged surface forms an RNA binding path from the concave to the convex side of MTERF4 and further along NSUN4 all of the way into the active site. This finding suggests that both subunits of the protein complex likely contribute to RNA recognition. The interface between MTERF4 and NSUN4 contains evolutionarily conserved polar and hydrophobic amino acids, and mutations that change these residues completely disrupt complex formation. This study provides a molecular explanation for MTERF4-dependent recruitment of NSUN4 to ribosomal RNA and suggests a unique mechanism by which other members of the large MTERF-family of proteins can regulate ribosomal biogenesis.
与呼吸链至关重要的蛋白质是由线粒体核糖体翻译的。因此，线粒体核糖体生物发生对于氧化磷酸化能力至关重要，并且已知干扰会导致人类疾病。这个复杂的过程在进化上是保守的，涉及到几个 RNA 加工和修饰步骤，这些步骤是正确的核糖体 RNA 成熟所必需的。我们最近表明，线粒体转录终止因子（MTERF）家族的蛋白质成员之一 MTERF4 将 5-甲基胞嘧啶 RNA 甲基转移酶 NSUN4 招募到大核糖体亚基，这是线粒体核糖体生物发生的关键步骤。在这里，我们描述了人类 MTERF4-NSUN4 复合物的 3D 晶体结构，分辨率为 2.9Å。MTERF4 由结构重复的 MTERF 基序组成，这些基序形成一个核酸结合结构域。NSUN4 缺乏通常用于相关 RNA 甲基转移酶识别 RNA 的 N 或 C 末端延伸。相反，NSUN4 结合到 MTERF4 的 C 末端。一个带正电荷的表面在 MTERF4 的凹面和凸面之间形成一个 RNA 结合路径，并沿着 NSUN4 一直延伸到活性位点。这一发现表明，蛋白质复合物的两个亚基可能都有助于 RNA 识别。MTERF4 和 NSUN4 之间的界面包含进化上保守的极性和疏水性氨基酸，并且改变这些残基的突变会完全破坏复合物的形成。这项研究为 MTERF4 依赖的 NSUN4 与核糖体 RNA 的募集提供了分子解释，并提出了一种独特的机制，其他大 MTERF 家族蛋白可以通过这种机制调节核糖体生物发生。
