Wang Y 2019 J Biol Chem
| Wang Y, Palmfeldt J, Gregersen N, Makhov AM, Conway JF, Wang M, McCalley SP, Basu S, Alharbi H, St Croix C, Calderon MJ, Watkins S, Vockley J (2019) Mitochondrial fatty acid oxidation and the electron transport chain comprise a multifunctional mitochondrial protein complex. J Biol Chem 294:12380-91. https://doi.org/10.1074/jbc.RA119.008680 |
Wang Y, Palmfeldt J, Gregersen N, Makhov AM, Conway JF, Wang M, McCalley SP, Basu S, Alharbi H, St Croix C, Calderon MJ, Watkins S, Vockley J (2019) J Biol Chem
Abstract: Three mitochondrial metabolic pathways are required for efficient energy production in eukaryotic cells: the electron transfer chain (ETC), fatty acid β-oxidation (FAO), and the tricarboxylic acid cycle. The ETC is organized into inner mitochondrial membrane supercomplexes that promote substrate channeling and catalytic efficiency. Although previous studies have suggested functional interaction between FAO and the ETC, their physical interaction has never been demonstrated. In this study, using blue native gel and two-dimensional electrophoreses, nano-LC-MS/MS, immunogold EM, and stimulated emission depletion microscopy, we show that FAO enzymes physically interact with ETC supercomplexes at two points. We found that the FAO trifunctional protein (TFP) interacts with the NADH-binding domain of complex I of the ETC, whereas the electron transfer enzyme flavoprotein dehydrogenase interacts with ETC complex III. Moreover, the FAO enzyme very-long-chain acyl-CoA dehydrogenase physically interacted with TFP, thereby creating a multifunctional energy protein complex. These findings provide a first view of an integrated molecular architecture for the major energy-generating pathways in mitochondria that ensures the safe transfer of unstable reducing equivalents from FAO to the ETC. They also offer insight into clinical ramifications for individuals with genetic defects in these pathways.
• Bioblast editor: Gnaiger E
Selected quotes and comments
Gnaiger E (2023-09-07)
- VLCAD is a homodimer containing a FAD cofactor that is the first step in the mitochondrial matrix for oxidation of the acyl-CoA substrate.
- The FAO-generated NADH and QH2 are potentially exposed to oxidation in the reactive environment of the mitochondrial matrix and rely on safe transfer of electron-reducing equivalents from NADH and QH2 to ETC to generate ATP.
- Comment: If electron flavoprotein dehydrogenase (ETFDH) is recognized as a mtIM-bound respiratory Complex (CETFDH), then it is clear that QH2 is generated within the membrane-bound electron transfer system (mETS), ETF but not QH2 transfers reducing equivalents to the mETS, and QH2 in the mtIM is not exposed to the mt-matrix.
- Thus, a suitable physical interaction is required to ensure the safe transfer of electron equivalents from FAO to ETC.
- Comment: It is helpful to distinguish FAO and beta-oxidation, since FAO includes (quote) 'transport of substrates into mitochondria through carnitine palmitoyltransferases I and II (CPTI and CPTII) linked by a carnitine-acylcarnitine translocase', beta-oxidation, and downstream transfer of reducing equivalents to O2 as the final electron acceptor.
- .. the FAO enzymes physically and functionally interact with the ETC supercomplexes, albeit more weakly than the interaction between ETC complexes in supercomplexes.
- ETFDH and Com III are predicted to contact each other, presumably in close approximation to the core II CoQ-binding subunit.
- TFP is linked both with the complex I NADH-binding domain and VLCAD, likely on opposite sides of the TFP molecule, whereas ETFDH interacts with complex III at its matrix side.
- For steps 1–3, long-chain acyl-CoA substrates are transferred into mitochondria as acylcarnitines, which cross from the intermembrane space into VLCAD through CPTII in the inner membrane. VLCAD then accepts and catalyzes the released long-chain acyl-CoA substrate to its enoyl–CoA product with reduction of ETF. The protein complex promotes metabolite channeling for all these reactions. For steps 4 and 5, reduced ETF is released from VLCAD into the mitochondrial matrix, where it is free to find its redox partner, ETFDH, and shuttle its reducing equivalents (QH2) to ETC complex III. Alternatively, for high catalytic efficiency of transfer of electrons from FAO to ETC, the ETF may remain associated with the macromolecular FAO–ETC complex and instead slide down the membrane-associated proteins to more efficiently contact ETFDH.
- The interaction between TFP/complex I and ETFDH/complex III can ensure safe transfer of electron equivalents to ETC and ultimate ATP generation.
Labels:
Enzyme: Complex I, Complex III, Supercomplex
Pathway: F
