Matta Srujan Kumar, Pareek Gautam, Bankapalli Kondalarao, Oblesha Anjaneya, D'Silva Patrick
Department of Biochemistry, Indian Institute of Science, Bangalore, India.
Department of Biochemistry, Indian Institute of Science, Bangalore, India
Mol Cell Biol. 2017 Mar 1;37(6). doi: 10.1128/MCB.00491-16. Print 2017 Mar 15.
Mitochondrial life cycle and protein import are intricate cellular processes, which require precise coordination between the transport machineries of outer and inner mitochondrial membranes. Presequence translocase performs the indispensable function of translocating preproteins having N-terminal targeting sequences across the inner membrane. Tim23 forms the core of the voltage-gated import channel, while Tim17 is presumed to maintain the stoichiometry of the translocase. However, mechanistic insights into how Tim17 coordinates these regulatory events within the complex remained elusive. We demonstrate that Tim17 harbors conserved G/AXXXG/A motifs within its transmembrane regions and plays an imperative role in the translocase assembly through interaction with Tim23. Tandem motifs are highly essential, as most of the amino acid substitutions lead to nonviability due to the complete destabilization of the TIM23 channel. Importantly, Tim17 transmembrane regions regulate the dynamic assembly of translocase to form either the TIM23 (PAM)-complex or TIM23 (SORT)-complex by recruiting the presequence translocase-associated motor (PAM) machinery or Tim21, respectively. To a greater significance, mutants displayed mitochondrial DNA (mtDNA) instability, membrane potential loss, and defective import, resulting in organellar dysfunction. We conclude that the integrity of Tim17 transmembrane regions is critical for mitochondrial function and protein turnover.
线粒体生命周期和蛋白质导入是复杂的细胞过程，需要线粒体外膜和内膜的转运机制之间精确协调。前序列转位酶执行将具有N端靶向序列的前体蛋白转运穿过内膜的不可或缺的功能。Tim23构成电压门控导入通道的核心，而Tim17被认为维持转位酶的化学计量。然而，关于Tim17如何在复合物中协调这些调节事件的机制见解仍然难以捉摸。我们证明Tim17在其跨膜区域含有保守的G/AXXXG/A基序，并通过与Tim23相互作用在转位酶组装中发挥至关重要的作用。串联基序非常重要，因为大多数氨基酸取代由于TIM23通道的完全不稳定而导致无法存活。重要的是，Tim17跨膜区域通过分别募集前序列转位酶相关马达（PAM）机制或Tim21来调节转位酶的动态组装，以形成TIM23（PAM）复合物或TIM23（SORT）复合物。更重要的是，突变体表现出线粒体DNA（mtDNA）不稳定、膜电位丧失和导入缺陷，导致细胞器功能障碍。我们得出结论，Tim17跨膜区域的完整性对于线粒体功能和蛋白质周转至关重要。
