Abstract

Mitochondrial shapes range from small oval fragments to interconnected networks of tubules that are constantly moving, fusing, and dividing. The innermost mitochondrial aqueous compartment, the matrix, is bounded by the highly convoluted inner membrane, which in turn is surrounded by the outer membrane. The inner membrane projects cristae into the matrix. Depending on the cell type and physiological conditions, the cristae can assume a variety of shapes, ranging from simple tubular to lamellar. Several key players, including the MICOS (mitochondrial contact site and cristae organising system) proteins, have been described to influence mitochondrial architecture. However, little is known about the distribution of such proteins within these organelles. A major challenge in obtaining a comprehensive view of the sub-mitochondrial localisation of proteins in mitochondria is that these organelles have a diameter close to the diffraction limited resolution of light microscopy, which largely precludes the use of conventional light microscopy to study sub-mitochondrial protein localisations. Using STED super-resolution microscopy and 3D scanning electron microscopy, we investigate sub-mitochondrial protein distributions in living and chemically fixed cells. Mic60, a subunit of the MICOS complex, and several of its interaction partners are arranged in complex patterns. The data suggest that MICOS is part of an extended multi-protein interaction network that scaffolds mitochondria.