期刊名称：Proceedings of the National Academy of Sciences
印刷版ISSN：0027-8424
电子版ISSN：1091-6490
出版年度：2014
卷号：111
期号：44
页码：E4697-E4705
DOI：10.1073/pnas.1413128111
语种：English
出版社：The National Academy of Sciences of the United States of America
摘要：SignificanceCoenzyme Q (CoQ) is a requisite component of the mitochondrial oxidative phosphorylation machinery that produces more than 90% of cellular ATP. Despite the discovery of CoQ more than 50 years ago, many aspects of its biosynthesis remain obscure. These include the functions of uncharacterized CoQ-related proteins whose disruption can cause human diseases. Our work reveals that one such protein, COQ9, is a lipid-binding protein that enables CoQ biosynthesis through its physical and functional interaction with COQ7, and via its stabilization of the entire CoQ biosynthetic complex. Unexpectedly, COQ9 achieves these functions by repurposing an ancient bacterial fold typically used for transcriptional regulation. Collectively, our work adds new insight into a core component of the CoQ biosynthesis process. Coenzyme Q (CoQ) is an isoprenylated quinone that is essential for cellular respiration and is synthesized in mitochondria by the combined action of at least nine proteins (COQ1-9). Although most COQ proteins are known to catalyze modifications to CoQ precursors, the biochemical role of COQ9 remains unclear. Here, we report that a disease-related COQ9 mutation leads to extensive disruption of the CoQ protein biosynthetic complex in a mouse model, and that COQ9 specifically interacts with COQ7 through a series of conserved residues. Toward understanding how COQ9 can perform these functions, we solved the crystal structure of Homo sapiens COQ9 at 2.4 [IMG]f1.gif" ALT="A" BORDER="0">. Unexpectedly, our structure reveals that COQ9 has structural homology to the TFR family of bacterial transcriptional regulators, but that it adopts an atypical TFR dimer orientation and is not predicted to bind DNA. Our structure also reveals a lipid-binding site, and mass spectrometry-based analyses of purified COQ9 demonstrate that it associates with multiple lipid species, including CoQ itself. The conserved COQ9 residues necessary for its interaction with COQ7 comprise a surface patch around the lipid-binding site, suggesting that COQ9 might serve to present its bound lipid to COQ7. Collectively, our data define COQ9 as the first, to our knowledge, mammalian TFR structural homolog and suggest that its lipid-binding capacity and association with COQ7 are key features for enabling CoQ biosynthesis.
