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Tetrahymena intramitochondrial filamentous inclusions contain 14-nm filament protein/citrate synthase
O Numata1, T Yasuda, Y Watanabe
1Institute of Biological Sciences, University of Tsukuba, Ibaraki, Japan.
Abstract:
Tetrahymena 14-nm filament protein has been shown to have dual functions as a citrate synthase in mitochondria and as a cytoskeletal protein in oral morphogenesis and pronuclear behavior during conjugation. Immunofluorescence studies of the 14-nm filament protein/citrate synthase in mitochondria found that intense mitochondrial fluorescence remained unchanged in Tetrahymena cells taken from logarithmic growth phase to stationary phase. However, electron microscopic studies showed that electron-dense rod-shaped structures found in mitochondrial matrices tended to increase in Tetrahymena cells in the growth decline phase. The rods were composed of side-by-side straight filaments with diameters of approximately 14 to 16 nm. Serial sections revealed that in Tetrahymena cells in growth decline phase, one to four electron-dense rods existed in the matrices of every mitochondrion. Immunoelectron microscopy using an anti-14-nm filament antibody clearly showed that a filament bundle of the electron-dense rod was the bundle of polymerized filaments of 14-nm filament protein/citrate synthase. These results strongly suggest that dynamic monomer-polymer conversion of the 14-nm filament protein/citrate synthase in mitochondria depends upon the physiological conditions of Tetrahymena cells.
Insights
Tetrahymena 14-nm filament protein, a dual-function enzyme, dynamically polymerizes within mitochondria during cell growth decline. This suggests its structure changes based on cellular conditions.
Area of Science:
- Cell Biology
- Biochemistry
- Microbiology
Background:
- Tetrahymena 14-nm filament protein exhibits dual roles: citrate synthase in mitochondria and cytoskeletal protein.
- Its mitochondrial function and cytoskeletal roles are known, but its dynamic behavior within mitochondria under varying physiological conditions requires further investigation.
Purpose of the Study:
- To investigate the dynamic changes and polymerization of the 14-nm filament protein/citrate synthase within Tetrahymena mitochondria.
- To correlate these changes with the physiological state of Tetrahymena cells.
Main Methods:
- Immunofluorescence microscopy to assess protein localization and abundance.
- Electron microscopy (EM) and serial sectioning to visualize mitochondrial structures.
- Immunoelectron microscopy to confirm the composition of observed structures.
Main Results:
- Mitochondrial fluorescence of the 14-nm filament protein/citrate synthase remained constant across growth phases.
- Electron-dense, rod-shaped structures (14-16 nm diameter filaments) increased in mitochondrial matrices during the growth decline phase.
- Immunoelectron microscopy confirmed these rods are bundles of polymerized 14-nm filament protein/citrate synthase.
Conclusions:
- The 14-nm filament protein/citrate synthase undergoes dynamic monomer-polymer conversion within Tetrahymena mitochondria.
- This polymerization is dependent on the physiological conditions of the Tetrahymena cells, particularly during growth decline.