Koripella Ravi K, Sharma Manjuli R, Haque Md Emdadul, Risteff Paul, Spremulli Linda L, Agrawal Rajendra K
Division of Translational Medicine, Wadsworth Center, New York State Department of Health, Albany, NY 12201-0509, USA.
Department of Chemistry, Campus Box 3290, University of North Carolina, Chapel Hill, NC, USA.
iScience. 2019 Feb 22;12:76-86. doi: 10.1016/j.isci.2018.12.030. Epub 2019 Jan 3.
The human mitochondrial translational initiation factor 3 (IF3) carries mitochondrial-specific amino acid extensions at both its N and C termini (N- and C-terminal extensions [NTE and CTE, respectively]), when compared with its eubacterial counterpart. Here we present 3.3- to 3.5-Å-resolution cryoelectron microscopic structures of the mammalian 28S mitoribosomal subunit in complex with human IF3. Unique contacts observed between the 28S subunit and N-terminal domain of IF3 explain its unusually high affinity for the 28S subunit, whereas the position of the mito-specific NTE suggests NTE's role in binding of initiator tRNA to the 28S subunit. The location of the C-terminal domain (CTD) clarifies its anti-association activity, whereas the orientation of the mito-specific CTE provides a mechanistic explanation for its role in destabilizing initiator tRNA in the absence of mRNA. Furthermore, our structure hints at a possible role of the CTD in recruiting leaderless mRNAs for translation initiation. Our findings highlight unique features of IF3 in mitochondrial translation initiation.
与细菌中的对应物相比，人类线粒体翻译起始因子3（IF3）在其N端和C端均带有线粒体特异性氨基酸延伸（分别为N端延伸和C端延伸 [NTE和CTE]）。在此，我们展示了与人类IF3结合的哺乳动物28S线粒体核糖体亚基的3.3至3.5埃分辨率的冷冻电子显微镜结构。在28S亚基与IF3的N端结构域之间观察到的独特接触解释了其对28S亚基异常高的亲和力，而线粒体特异性NTE的位置表明NTE在起始tRNA与28S亚基结合中的作用。C端结构域（CTD）的位置阐明了其抗缔合活性，而线粒体特异性CTE的方向为其在无mRNA时使起始tRNA不稳定的作用提供了机制解释。此外，我们的结构暗示CTD在募集无领导mRNA进行翻译起始中可能发挥的作用。我们的研究结果突出了IF3在线粒体翻译起始中的独特特征。
