Carbon and Nitrogen Sources Have No Impact on the Organization and Composition of Ustilago maydis Respiratory Supercomplexes

Abstract

Respiratory supercomplexes are found in mitochondria of eukaryotic cells and some bacteria. A hypothetical role of these supercomplexes is electron channeling, which in principle should increase the respiratory chain efficiency and ATP synthesis. In addition to the four classic respiratory complexes and the ATP synthase, U. maydis mitochondria contain three type II NADH dehydrogenases (NADH for reduced nicotinamide adenine dinucleotide) and the alternative oxidase. Changes in the composition of the respiratory supercomplexes due to energy requirements have been reported in certain organisms. In this study, we addressed the organization of the mitochondrial respiratory complexes in U. maydis under diverse energy conditions. Supercomplexes were obtained by solubilization of U. maydis mitochondria with digitonin and separated by blue native polyacrylamide gel electrophoresis (BN-PAGE). The molecular mass of supercomplexes and their probable stoichiometries were 1200 kDa (I1:IV1), 1400 kDa (I1:III2), 1600 kDa (I1:III2:IV1), and 1800 kDa (I1:III2:IV2). Concerning the ATP synthase, approximately half of the protein is present as a dimer and half as a monomer. The distribution of respiratory supercomplexes was the same in all growth conditions. We did not find evidence for the association of complex II and the alternative NADH dehydrogenases with other respiratory complexes.

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“…In Fig. 4B, the mitochondrial SCs are identi ed by BN-PAGE in the different treatment schemes; the rst lane corresponds to bovine heart mitochondria previously solubilized with lauryl maltoside, a detergent that does not preserve interactions between SCs, and, therefore, it can be used to observe mitochondrial complexes in their monomeric form; this sample was used as a molecular weight marker since the bands corresponding to each mitochondrial complex are widely reported previously (32). In the other lanes, the activity bands corresponding to supercomplex I (SC I) of the experimental group samples are shown to identify bands in which mitochondrial SCs are positioned compared with the activity of SC II, IV, and V (Fig.…”

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“…Supercomplex formation of respiratory chain complexes is thought to help in cellular adaptation to conditions of increased energy need. They found the existence of four distinct supercomplexes (associations of complex I 1 with III 2 , I 1 with IV 1 , I 1 with III 2 and IV 1 , as well as I 1 with III 2 and IV 2 ) that were not found to associate with complex II, the alternative NADH dehydrogenases, or with ATP synthase, and also were not affected by growth conditions [ 16 ]. Zooming out to the population level, M.S.…”