MITOCHONDRIA IN CHAOS

Yuru Deng (1), Mike Marko (1), Karolyn Buttle (1), ArDean Leith (1) and Carmen A. Mannella (1,2)
(1) Wadsworth Center, New York State Department of Health, Albany, NY
(2) Department of Biomedical Sciences, University at Albany (SUNY)

Computer simulation of TEM images of mitochondria in unfed amoeba Chaos carolinensis has indicated that the highly curved cristae correspond to periodic cubic surfaces, a mathematical model analogous to periodic minimal surface in describing lipidic cubic phases [1]. The existence of this crystal-like cubic membrane structure has been observed in numerous cell lines throughout the plant and animal kingdoms. So far the detailed structural analysis has been based on 2D projections instead of true 3D structure. In order to directly prove the 3D structure of Chaos mitochondria, double-tilt tomographic reconstructions have been obtained from quarter-micron sections cut from the same conventionally prepared EM blocks used in the previous work [1]. Comparison of projections along characteristic lattice directions (e.g., 100, 110, 111) in the tomographic reconstruction and a mathematical model show that the two converge to the same 3D structure. Analysis of the continuous membrane surfaces in the reconstruction further explains the connectivity of the compartments within the amoeba mitochondria. In the cubic regions, the matrix is hyper-condensed and confined to one continuous, small space between adjacent cristal membranes. The intracristal compartments form large, regularly spaced cisternae, which communicate with the peripheral compartment through tubular segments as in other types of mitochondria. The cubic membrane structure of amoeba mitochondria may be an ideal specimen for measuring geometrical distortions in biological electron tomography. It may also provide a useful model system for studying the organization of cristae and its relation to mitochondrial activity.

[1] Deng Y, Mieczkowski M. (1998) Protoplasma 203:16-25.