Structure of the ATP-Synthase from Chloroplasts and Mitochondria Studied by Electron Microscopy

The structure of the ATP-synthase, F0F1 , from spinach chloroplasts and beef heart mitochondria has been investigated by electron microscopy with negatively stained specimens. The detergent-solubilized ATP-synthase forms string-like structures in which the F0 parts are aggregated. In most cases, the F, parts are arranged at alternating sides along the string. The F0 part has an approximate cylindrical shape with heights of 8.3 and 8.9 nm and diameters of 6.2 and 6.4 nm for the chloroplast and mitochondrial enzyme, respectively. The F, parts are disk-like structures with a diameter of about 11.5 nm and a height of about 8.5 nm. The F, parts are attached to the strings, composed of Fn parts, in most cases, with their smallest dimension parallel to the strings. The stalk connecting F0 and F, has a length of 3.7 nm and 4.3 nm and a diameter of 2.7 nm and 4.3 nm for the chloroplast and mitochondrial enzyme, respectively

Supramolecular Structure of the Mitochondrial Oxidative Phosphorylation System

The protein complexes of the mitochondrial oxidative phosphorylation system were recently reported to form supramolecular assemblies termed respiratory supercomplexes or respirasomes. These supercomplexes are considered to be of great functional importance. Here we review new insights into supercomplex structure and physiology

Single particle electron microscopy

Electron microscopy (EM) in combination with image analysis is a powerful technique to study protein structures at low, medium, and high resolution. Since electron micrographs of biological objects are very noisy, improvement of the signal-to-noise ratio by image processing is an integral part of EM, and this is performed by averaging large numbers of individual projections. Averaging procedures can be divided into crystallographic and non-crystallographic methods. The crystallographic averaging method, based on two-dimensional (2D) crystals of (membrane) proteins, yielded in solving atomic protein structures in the last century. More recently, single particle analysis could be extended to solve atomic structures as well. It is a suitable method for large proteins, viruses, and proteins that are difficult to crystallize. Because it is also a fast method to reveal the low-to-medium resolution structures, the impact of its application is growing rapidly. Technical aspects, results, and possibilities are presented

Characterization by electron microscopy of dimeric Photosystem II core complexes from spinach with and without CP43

Dimeric associations of the D1-D2-CP47 and D1-D2-CP47-CP43 complexes of Photosystem II from spinach were isolated and purified with sucrose density gradient centrifugation and gel filtration chromatography and analyzed by electron microscopy and image analysis. Images of both preparations show characteristic details in protein density. The location of the CP43 subunit and the way the dimers are associated could be determined from a comparison between diamond-like monomeric projections of the D1-D2-CP47-CP43 complex (maximal dimensions along the diagonals 10–12 and 7–8 nm) and triangle-like monomeric projections of the D1-D2-CP47 complex (dimensions 8–9 and 7–8 nm). Both isolated complexes have different dimeric configurations than observed before in several other dimeric complexes, and based on biochemical considerations we conclude that both newly observed configurations are artificial. The observation of the artificial aggregates, however, allows conclusions on the organization of Photosystem II in two-dimensional crystals and on the size of the monomeric unit. We propose a model for the location of D1, D2, CP43 and CP47 in the Photosystem II core complex in which CP43 and CP47 are positioned at the tips of the monomeric unit, closely connected to D2 and D1, respectively.