The inhibitor protein IF from mammalian mitochondria inhibits ATP hydrolysis but not ATP synthesis by the ATP synthase complex.

The hydrolytic activity of the ATP synthase in bovine mitochondria is inhibited by a protein called IF, but bovine IF has no effect on the synthetic activity of the bovine enzyme in mitochondrial vesicles in the presence of a proton motive force. In contrast, it has been suggested based on indirect observations that human IF inhibits both the hydrolytic and synthetic activities of the human ATP synthase and that the activity of human IF is regulated by the phosphorylation of Ser-14 of mature IF. Here, we have made both human and bovine IF which are 81 and 84 amino acids long, respectively, and identical in 71.

Two independent respiratory chains adapt OXPHOS performance to glycolytic switch.

The structural and functional organization of the mitochondrial respiratory chain (MRC) remains intensely debated. Here, we show the co-existence of two separate MRC organizations in human cells and postmitotic tissues, C-MRC and S-MRC, defined by the preferential expression of three COX7A subunit isoforms, COX7A1/2 and SCAFI (COX7A2L). COX7A isoforms promote the functional reorganization of distinct co-existing MRC structures to prevent metabolic exhaustion and MRC deficiency.

Key features of inhibitor binding to the human mitochondrial pyruvate carrier hetero-dimer.

Objective: The mitochondrial pyruvate carrier (MPC) has emerged as a promising drug target for metabolic disorders, including non-alcoholic steatohepatitis and diabetes, metabolically dependent cancers and neurodegenerative diseases. A range of structurally diverse small molecule inhibitors have been proposed, but the nature of their interaction with MPC is not understood, and the composition of the functional human MPC is still debated. The goal of this study was to characterise the human MPC protein in vitro, to understand the chemical features that determine binding of structurally diverse inhibitors and to develop novel higher affinity ones.

ND3 Cys39 in complex I is exposed during mitochondrial respiration.

Mammalian complex I can adopt catalytically active (A-) or deactive (D-) states. A defining feature of the reversible transition between these two defined states is thought to be exposure of the ND3 subunit Cys39 residue in the D-state and its occlusion in the A-state. As the catalytic A/D transition is important in health and disease, we set out to quantify it by measuring Cys39 exposure using isotopic labeling and mass spectrometry, in parallel with complex I NADH/CoQ oxidoreductase activity.

NDUFS3 depletion permits complex I maturation and reveals TMEM126A/OPA7 as an assembly factor binding the ND4-module intermediate.

Complex I (CI) is the largest enzyme of the mitochondrial respiratory chain, and its defects are the main cause of mitochondrial disease. To understand the mechanisms regulating the extremely intricate biogenesis of this fundamental bioenergetic machine, we analyze the structural and functional consequences of the ablation of NDUFS3, a non-catalytic core subunit. We show that, in diverse mammalian cell types, a small amount of functional CI can still be detected in the complete absence of NDUFS3.