Molecular mechanism of interactions between ACAD9 and binding partners in mitochondrial respiratory complex I assembly

Chuanwu Xia; Baoying Lou; Zhuji Fu; Al-Walid Mohsen; Anna L Shen; Jerry Vockley; Jung-Ja P Kim

doi:10.1016/j.isci.2021.103153

Molecular mechanism of interactions between ACAD9 and binding partners in mitochondrial respiratory complex I assembly

iScience. 2021 Sep 22;24(10):103153. doi: 10.1016/j.isci.2021.103153. eCollection 2021 Oct 22.

Authors

Chuanwu Xia¹, Baoying Lou¹, Zhuji Fu¹, Al-Walid Mohsen^{2

3}, Anna L Shen⁴, Jerry Vockley^{2

3}, Jung-Ja P Kim¹

Affiliations

¹ Department of Biochemistry, Medical College of Wisconsin, Milwaukee, WI 53226, USA.
² Department of Pediatrics, School of Medicine, University of Pittsburgh, Children's Hospital of Pittsburgh of UPMC, Pittsburgh, PA 15224, USA.
³ Department of Human Genetics, School of Public Health, University of Pittsburgh, Pittsburgh, PA 15213, USA.
⁴ McArdle Laboratory for Cancer Research, Department of Oncology, University of Wisconsin-Madison, Madison, WI 53706, USA.

Abstract

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.

Keywords: Biological sciences; Molecular biology; Structural biology.

Abstract

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