From the Laboratory of Cell Biology, Center for Cancer Research, National Cancer Institute, National Institutes of Health, Bethesda, Maryland 20892,
Published: November 2016
AI Article Synopsis
Article Abstract
Complex III or the cytochrome (cyt) bc complex constitutes an integral part of the respiratory chain of most aerobic organisms and of the photosynthetic apparatus of anoxygenic purple bacteria. The function of cyt bc is to couple the reaction of electron transfer from ubiquinol to cytochrome c to proton pumping across the membrane. Mechanistically, the electron transfer reaction requires docking of its Rieske iron-sulfur protein (ISP) subunit to the quinol oxidation site (Q) of the complex. Formation of an H-bond between the ISP and the bound substrate was proposed to mediate the docking. Here we show that the binding of oxazolidinedione-type inhibitors famoxadone, jg144, and fenamidone induces docking of the ISP to the Q site in the absence of the H-bond formation both in mitochondrial and bacterial cyt bc complexes, demonstrating that ISP docking is independent of the proposed direct ISP-inhibitor interaction. The binding of oxazolidinedione-type inhibitors to cyt bc of different species reveals a toxophore that appears to interact optimally with residues in the Q site. The effect of modifications or additions to the toxophore on the binding to cyt bc from different species could not be predicted from structure-based sequence alignments, as demonstrated by the altered binding mode of famoxadone to bacterial cyt bc.
Pulmonary artery endothelial cells (PAECs) are a major contributor to hypoxic pulmonary hypertension (PH) due to the possible roles of reactive oxygen species (ROS). However, the molecular mechanisms and functional roles of ROS in PAECs are not well established. In this study, we first used Amplex UltraRed reagent to assess hydrogen peroxide (HO) generation.
- A rare genetic condition involving mitochondrial complex III deficiency and lactic acidosis, characterized by scalp alopecia, was identified in two unrelated cases and discussed further with a participant from the Undiagnosed Diseases Network (UDN).
- The participant had two autosomal recessive disorders discovered through genome sequencing: mitochondrial complex III deficiency and cataracts, with specifics on previously documented pathogenic variants for each condition.
- A combination of enzyme assays and cellular proteomics showed clear dysfunction in complex III and low levels of a crucial protein, validating the genetic mutations' pathogenic effects and broadening understanding of these rare disorders.
Arabidopsis uracil phosphoribosyltransferase (UPP) is an essential enzyme and plants lacking this enzyme are strongly compromised in chloroplast function. Our analysis of UPP amiRNA mutants has confirmed that this vital function is crucial to establish a fully functional photosynthesis as the RIESKE iron sulfur protein (PetC) is almost absent, leading to a block in photosynthetic electron transport. Interestingly, this function appears to be unrelated to nucleotide homeostasis since nucleotide levels were not altered in the studied mutants.
Rieske oxygenases catalyze an exceptionally broad range of discrete types of reactions despite the utilization of a highly conserved quaternary structure and metal cofactor complement. Oxygen activation within this family occurs at a mononuclear Fe site, which is located approximately 12 Å from a one-electron reduced Rieske-type iron-sulfur cluster. Electron transfer from the Rieske cluster to the mononuclear iron site occurs during O activation and product formation.
The biotechnological potential of Rieske Oxygenases (ROs) and their cognate reductases remains unmet, in part because these systems can be functionally short-lived. Here, we describe a set of experiments aimed at identifying both the functional and structural stability limitations of ROs, using terephthalate (TPA) dioxygenase (from Comamonas strain E6) as a model system. Successful expression and purification of a cofactor-complete, histidine-tagged TPA dioxygenase and reductase protein system requires induction with the Escherichia coli host at stationary phase as well as a chaperone inducing cold-shock and supplementation with additional iron, sulfur, and flavin.
