1,721,122 research outputs found
How evolution dismantles and reassembles multienzyme complexes
Full text linkThe mycobacterial PDH features an unusual architecture that may allow it to function in combination with otherα-ketoacid dehydrogenase complexes. This design may reflect specific metabolic and regulatory needs by Mycobacteria and related microorganism
Structure and mechanisms of ROS generation by NADPH oxidases
No full textNADPH oxidases (NOXs) are integral membrane enzymes that produce reactive oxygen species. Humans have seven NOX enzymes that feature a very similar catalytic core but distinct regulatory mechanisms. The recent structural elucidation of the NOX catalytic domains has been a step forward in the field. NADPH, FAD, and two hemes form a linear array of redox cofactors that transfer electrons across to the two sides of the membrane. Oxygen is reduced through an unusual outer sphere mechanism that does not involve any covalent intermediate with the heme iron. Several recent studies have expanded the roles of NOXs in cell signaling, innate immune response, and cell proliferation including oncogenic transformation. This work reinforces NOX-generated ROS as powerful signaling molecules. A challenging question is to understand the specific mechanisms of enzyme regulation and to harness the growing insight on NOXs' structure and biochemistry to generate more powerful small-molecule modulators of NOX activities
Editorial overview: Biological catalysis at the cross-roads of signaling and metabolism
Full text linkEnzymes are the principal catalysts in biology and comprise a large propor- tion of the proteins encoded by the human genome. Although much has been learned about enzymes over the past century, there are still major gaps in our fundamental knowledge about how enzymes catalyze reactions, what specific substrates are processed by particular enzymes, how enzymes are turned off or on in cellular pathways, and how they influence health and disease. There are increasing numbers of therapeutics that work as enzyme inhibitors and structure-based design is becoming an important part of the arsenal of drug discovery efforts. New technologies involving chemical, biophysical, genetic, and physiologic approaches are changing the landscape of enzyme research and leading to impactful discoveries in enzymology. This issue of COSTBI includes a series of articles that summarize recent advances in the enzyme sciences
Biosynthetic Strategies of Berberine Bridge Enzyme-like Flavoprotein Oxidases toward Structural Diversification in Natural Product Biosynthesis
No full textBerberine bridge enzyme-like oxidases are often involved in natural product biosynthesis and are seen as essential enzymes for the generation of intricate pharmacophores. These oxidases have the ability to transfer a hydride atom to the FAD cofactor, which enables complex substrate modifications and rearrangements including (intramolecular) cyclizations, carbon-carbon bond formations, and nucleophilic additions. Despite the diverse range of activities, the mechanistic details of these reactions often remain incompletely understood. In this Review, we delve into the complexity that BBE-like oxidases from bacteria, fungal, and plant origins exhibit by providing an overview of the shared catalytic features and emphasizing the different reactivities. We propose four generalized modes of action by which BBE-like oxidases enable the synthesis of natural products, ranging from the classic alcohol oxidation reactions to less common amine and amide oxidation reactions. Exploring the mechanisms utilized by nature to produce its vast array of natural products is a subject of considerable interest and can lead to the discovery of unique biochemical activities
A lonely electron blocks incoming pairs
No full textElectron bifurcation exploits high energetic states to drive unfavorable single electron reactions and determining the overall mechanism governing these electron transfers represents an arduous task. Using extensive stopped-flow spectroscopy and kinetic simulations, Sucharitakul et al. now explore the bifurcation mechanism of the electron transfer flavoprotein EtfAB from the anaerobic gut bacterium Acidaminococcus fermentans. Strikingly, they illustrated that catalysis is orchestrated by a negatively charged radical, α-FAD, that inhibits further reductions and features an atypical inverted kinetic isotope effect. These results provide additional insight behind electron transfers that are prevalent within multienzyme governed reactions
Baeyer-Villiger Monooxygenases and Their Mechanism of Oxygen Activation: From Microbes to Humans
No full textAn elegant four-helical fold in NOX and STEAP enzymes facilitates electron transport across biomembranes - Similar vehicle, different destination
Full text linkConspectusThe ferric reductase superfamily comprises several oxidoreductases that use an intracellular electron source to reduce an extracellular acceptor substrate. NADPH oxidases (NOXs) and six-transmembrane epithelial antigen of the prostate enzymes (STEAPs) are iconic members of the superfamily. NOXs produce extracellular reactive oxygen species that exert potent bactericidal activities and trigger redox-signaling cascades that regulate cell division and differentiation. STEAPs catalyze the reduction of extracellular iron and copper which is necessary for the bioavailability of these essential elements. Both NOXs and STEAPs are present as multiple isozymes with distinct regulatory properties and physiological roles. Despite the important roles of NOXs and STEAPs in human physiology and despite their wide involvement in diseases like cancer, their mode of action at the molecular level remained incompletely understood for a long time, in part due to the absence of high-resolution models of the complete enzymes. Our two laboratories have elucidated the three-dimensional structures of NOXs and STEAPs, providing key insight into their mechanisms and evolution. The enzymes share a conserved transmembrane helical domain with an eye-catching hourglass shape. On the extracellular side, a heme prosthetic group is at the bottom of a pocket where the substrate (O2 in NOX, chelated iron or copper in STEAP) is reduced. On the intracellular side, the inner heme of NOX and the FAD of STEAP are bound to topological equivalent sites. This is a rare case where critical amino acid substitutions and local conformational changes enable a cofactor (heme vs FAD) swap between two structurally and functionally conserved scaffolds. The catalytic core of these enzymes is completed by distinct cytosolic NADPH-binding domains that are topologically unrelated (a ferredoxin reductase-like flavoprotein domain in NOX and a F420H2:NADP+-like domain in STEAP), feature different quaternary structures, and underlie specific regulatory mechanisms. Despite their differences, these domains all establish electron-transfer chains that direct the electrons from NADPH to the transmembrane domain. The multistep nature of the process and the chemical nature of the products pose considerable problems in the enzymatic assays. We learned that great care must be exerted in the validation of a candidate inhibitor. Multiple orthogonal assays are required to rule out off-target effects such as ROS-scavenging activities or nonspecific interference with the enzyme redox chain. The structural analysis of STEAP/NOX enzymes led us to further notice that their transmembrane heme-binding topology is shared by other enzymes. We found that the core domain of the cytochrome b subunits of the mitochondrial complex III and photosynthetic cytochrome b6f are closely related to NOXs and STEAPs and likely arose from the same ancestor protein. This observation expands the substrate portfolio of the superfamily since cytochromes b act on ubiquinone. The rigidly packed helices of the NOX/STEAP/cytochrome b domain contrast with the more malleable membrane proteins like ion channels or amino-acid transporters, which undergo large conformational changes to allow passage of relatively large metabolites. This notion of a rigid hourglass scaffold found an unexpected confirmation in the observation, revealed by structural comparisons, that an helical bundle identical to the NOX/STEAP/cytochrome b enzymes is featured by a de novo designed heme-binding protein, PS1. Apparently, nature and protein designers have independently converged to this fold as a versatile scaffold for heme-mediated reactions. The challenge is now to uncover the molecular mechanisms that implement the isozyme-specific regulation of the enzyme functions and develop much needed inhibitors and modulators for chemical biology and drug design studies
Regolare la rabbia: quale strategia? Uno studio preliminare
No full textRiassunto
La regolazione emotiva è una capacità di fondamentale importanza per il funzionamento ottimale dell'individuo che nell'ultimo ventennio ha catturato l'attenzione degli studiosi portando ad un incremento degli studi sul tema. Pochi articoli si sono concentrati sullo studio della regolazione della rabbia, emozione primaria tanto importante quanto rappresentata nella quotidianità. Lo studio qui presentato, prendendo spunto dal lavoro di Sheppes e colleghi (2011), ha voluto indagare il modo in cui due strategie, reinterpretazione e soppressione, vengono scelte per gestire la rabbia provata. I risultati indicano che la soppressione è la strategia più utilizzata per regolare questa emozione. Le implicazioni di questi risultati vengono discusse alla luce delle recenti scoperte sulla regolazione emozionale.
Abstract
In the present paper, we present results from an experiment about the regulation of anger in a sample of 26 volunteers (f=14, mean age=24.9, mean education=17.4). In a social interaction task, participants were presented with verbal stimuli either anger provoking or emotionally neutral associated with neutral faces of simulated participants. After each anger provoking and neutral situation they were asked to rate the level of perceived anger and to choose between three different options to regulate the emotion: reappraisal, suppression or no strategy. Results indicate that participants correctly perceived anger provoking stimuli and that suppression was the most used strategy for anger regulation. Notably, previous studies using self-reported measures, reported that reappraisal was the most effective strategy to regulate anger. This study thus expands previous findings and point toward the direction of a shift toward suppression based strategies when confronted with real social interactions that elicit anger
- …
