Xia Chuanwu, Lou Baoying, Fu Zhuji, Mohsen Al-Walid, Shen Anna L, Vockley Jerry, Kim Jung-Ja P
Department of Biochemistry, Medical College of Wisconsin, Milwaukee, WI 53226, USA.
Department of Pediatrics, School of Medicine, University of Pittsburgh, Children's Hospital of Pittsburgh of UPMC, Pittsburgh, PA 15224, USA.
iScience. 2021 Sep 22;24(10):103153. doi: 10.1016/j.isci.2021.103153. eCollection 2021 Oct 22.
The dual function protein ACAD9 catalyzes α,β-dehydrogenation of fatty acyl-CoA thioesters in fatty acid β-oxidation and is an essential chaperone for mitochondrial respiratory complex I (CI) assembly. ACAD9, ECSIT, and NDUFAF1 interact to form the core mitochondrial CI assembly complex. Current studies examine the molecular mechanism of ACAD9/ECSIT/NDUFAF1interactions. ACAD9 binds to the carboxy-terminal half and NDUFAF1 to the amino-terminal half of ECSIT. Binary complexes are unstable and aggregate easily, while the ACAD9/ECSIT/NDUFAF1 ternary complex is soluble and highly stable. Molecular modeling and small-angle X-ray scattering studies identified intra-complex interaction sites and binding sites for other assembly factors. Binding of ECSIT at the ETF binding site in the amino-terminal domain of ACAD9 is consistent with observed loss of FAD and enzymatic activity and demonstrates that the two functions of ACAD9 are mutually exclusive. Mapping of 42 known pathogenic mutations onto the homology-modeled ACAD9 structure provides structural insights into pathomechanisms of CI deficiency.
双功能蛋白ACAD9在脂肪酸β-氧化过程中催化脂肪酰辅酶A硫酯的α,β-脱氢反应，并且是线粒体呼吸复合体I（CI）组装所必需的伴侣蛋白。ACAD9、ECSIT和NDUFAF1相互作用形成线粒体CI组装核心复合体。目前的研究探讨了ACAD9/ECSIT/NDUFAF1相互作用的分子机制。ACAD9与ECSIT的羧基末端一半结合，而NDUFAF1与ECSIT的氨基末端一半结合。二元复合体不稳定且容易聚集，而ACAD9/ECSIT/NDUFAF1三元复合体是可溶且高度稳定的。分子建模和小角X射线散射研究确定了复合体内部的相互作用位点以及其他组装因子的结合位点。ECSIT在ACAD9氨基末端结构域的ETF结合位点处的结合与观察到的FAD和酶活性丧失一致，并表明ACAD9的两种功能相互排斥。将42个已知的致病突变映射到同源建模的ACAD9结构上，为CI缺乏的发病机制提供了结构上的见解。
