The structure of Na+-translocating of NADH:ubiquinone oxidoreductase of Vibrio cholerae: implications on coupling between electron transfer and Na+ transport

2015 ◽  
Vol 396 (9-10) ◽  
pp. 1015-1030 ◽  
Author(s):  
Julia Steuber ◽  
Georg Vohl ◽  
Valentin Muras ◽  
Charlotte Toulouse ◽  
Björn Claußen ◽  
...  
Keyword(s):  
Electron Transfer ◽  
Vibrio Cholerae ◽  
Conformational Changes ◽  
Cytoplasmic Membrane ◽  
Nadh:Ubiquinone Oxidoreductase ◽  
Effective Electron ◽  
X Ray ◽  
Electron Transfer Pathway ◽  
Quinone Reduction ◽  
Redox Centers

Abstract The Na+-translocating NADH:ubiquinone oxidoreductase (Na+-NQR) of Vibrio cholerae is a respiratory complex that couples the exergonic oxidation of NADH to the transport of Na+ across the cytoplasmic membrane. It is composed of six different subunits, NqrA, NqrB, NqrC, NqrD, NqrE, and NqrF, which harbor FAD, FMN, riboflavin, quinone, and two FeS centers as redox co-factors. We recently determined the X-ray structure of the entire Na+-NQR complex at 3.5-Å resolution and complemented the analysis by high-resolution structures of NqrA, NqrC, and NqrF. The position of flavin and FeS co-factors both at the cytoplasmic and the periplasmic side revealed an electron transfer pathway from cytoplasmic subunit NqrF across the membrane to the periplasmic NqrC, and via NqrB back to the quinone reduction site on cytoplasmic NqrA. A so far unknown Fe site located in the midst of membrane-embedded subunits NqrD and NqrE shuttles the electrons over the membrane. Some distances observed between redox centers appear to be too large for effective electron transfer and require conformational changes that are most likely involved in Na+ transport. Based on the structure, we propose a mechanism where redox induced conformational changes critically couple electron transfer to Na+ translocation from the cytoplasm to the periplasm through a channel in subunit NqrB.

scholarly journals A Quinol Anion as Catalytic Intermediate Coupling Proton Translocation With Electron Transfer in E. coli Respiratory Complex I

2021 ◽  
Vol 9 ◽  
Author(s):  
Franziska Nuber ◽  
Luca Mérono ◽  
Sabrina Oppermann ◽  
Johannes Schimpf ◽  
Daniel Wohlwend ◽  
...  
Keyword(s):  
Electron Transfer ◽  
Complex I ◽  
Proton Translocation ◽  
Difference Spectrum ◽  
Nadh:Ubiquinone Oxidoreductase ◽  
Protonmotive Force ◽  
Respiratory Complex ◽  
Quinone Reduction ◽  
Vis Spectroscopy ◽  
Respiratory Complex I

Energy-converting NADH:ubiquinone oxidoreductase, respiratory complex I, plays a major role in cellular energy metabolism. It couples NADH oxidation and quinone reduction with the translocation of protons across the membrane, thus contributing to the protonmotive force. Complex I has an overall L-shaped structure with a peripheral arm catalyzing electron transfer and a membrane arm engaged in proton translocation. Although both reactions are arranged spatially separated, they are tightly coupled by a mechanism that is not fully understood. Using redox-difference UV-vis spectroscopy, an unknown redox component was identified in Escherichia coli complex I as reported earlier. A comparison of its spectrum with those obtained for different quinone species indicates features of a quinol anion. The re-oxidation kinetics of the quinol anion intermediate is significantly slower in the D213GH variant that was previously shown to operate with disturbed quinone chemistry. Addition of the quinone-site inhibitor piericidin A led to strongly decreased absorption peaks in the difference spectrum. A hypothesis for a mechanism of proton-coupled electron transfer with the quinol anion as catalytically important intermediate in complex I is discussed.

scholarly journals Architecture of the mycobacterial succinate dehydrogenase with a membrane-embedded Rieske FeS cluster

2021 ◽  
Vol 118 (15) ◽  
pp. e2022308118
Author(s):  
Xiaoting Zhou ◽  
Yan Gao ◽  
Weiwei Wang ◽  
Xiaolin Yang ◽  
Xiuna Yang ◽  
...  
Keyword(s):  
Electron Transfer ◽  
Succinate Dehydrogenase ◽  
Krebs Cycle ◽  
Water Soluble ◽  
Electron Transfer Mechanism ◽  
Complex Ii ◽  
Electron Transfer Pathway ◽  
Quinone Binding ◽  
Reduction Activity ◽  
Quinone Reduction

Complex II, also known as succinate dehydrogenase (SQR) or fumarate reductase (QFR), is an enzyme involved in both the Krebs cycle and oxidative phosphorylation. Mycobacterial Sdh1 has recently been identified as a new class of respiratory complex II (type F) but with an unknown electron transfer mechanism. Here, using cryoelectron microscopy, we have determined the structure of Mycobacterium smegmatis Sdh1 in the presence and absence of the substrate, ubiquinone-1, at 2.53-Å and 2.88-Å resolution, respectively. Sdh1 comprises three subunits, two that are water soluble, SdhA and SdhB, and one that is membrane spanning, SdhC. Within these subunits we identified a quinone-binding site and a rarely observed Rieske-type [2Fe-2S] cluster, the latter being embedded in the transmembrane region. A mutant, where two His ligands of the Rieske-type [2Fe-2S] were changed to alanine, abolished the quinone reduction activity of the Sdh1. Our structures allow the proposal of an electron transfer pathway that connects the substrate-binding and quinone-binding sites. Given the unique features of Sdh1 and its essential role in Mycobacteria, these structures will facilitate antituberculosis drug discovery efforts that specifically target this complex.

scholarly journals The C-terminal tail of the bacterial translocation ATPase SecA modulates its activity

2018 ◽  
Author(s):  
Mohammed Jamshad ◽  
Timothy J. Knowles ◽  
Scott A. White ◽  
Douglas G. Ward ◽  
Fiyaz Mohammed ◽  
...  
Keyword(s):  
Conformational Changes ◽  
Metal Binding ◽  
Cytoplasmic Membrane ◽  
Protein Recognition ◽  
X Ray ◽  
Ribosome Binding ◽  
X Ray Crystallography ◽  
Substrate Protein ◽  
Metal Binding Domain

AbstractIn bacteria, the translocation of a subset of proteins across the cytoplasmic membrane by the Sec machinery requires SecA. Although SecA can recognise nascent polypeptides, the mechanism of cotranslational substrate protein recognition is not known. Here, we investigated the role of the C-terminal tail (CTT) of SecA, which consists of a flexible linker (FLD) and a small metal-binding domain (MBD), in its interaction with nascent polypeptides. Phylogenetic analysis and ribosome binding experiments indicated that the MBD interacts with 70S ribosomes. Disruption of the entire CTT or the MBD alone had opposing effects on ribosome binding, substrate-protein binding, ATPase activity and in vivo function. Autophotocrosslinking, mass spectrometry, x-ray crystallography and small-angle x-ray scattering experiments provided insight into the CTT-mediated conformational changes in SecA. Finally, photocrosslinking experiments indicated that binding of SecA to substrate protein affected its interaction with the ribosome. Taken together, our results suggest a mechanism for substrate protein recognition.Impact StatementSecA is an evolutionarily conserved ATPase that is required for the translocation of a subset of proteins across the cytoplasmic membrane in bacteria. We investigated how SecA recognises its substrate proteins at the ribosome as they are still being synthesised (i.e. cotranslationally).

scholarly journals X-ray structure of the direct electron transfer-type FAD glucose dehydrogenase catalytic subunit complexed with a hitchhiker protein

2019 ◽  
Vol 75 (9) ◽  
pp. 841-851 ◽  
Author(s):  
Hiromi Yoshida ◽  
Katsuhiro Kojima ◽  
Masaki Shiota ◽  
Keiichi Yoshimatsu ◽  
Tomohiko Yamazaki ◽  
...  
Keyword(s):  
Electron Transfer ◽  
Disulfide Bonds ◽  
Hydrophobic Interactions ◽  
Direct Electron Transfer ◽  
Glucose Dehydrogenase ◽  
Catalytic Subunit ◽  
Effective Electron ◽  
Α Subunit ◽  
X Ray ◽  
Membrane Bound

The bacterial flavin adenine dinucleotide (FAD)-dependent glucose dehydrogenase complex derived from Burkholderia cepacia (BcGDH) is a representative molecule of direct electron transfer-type FAD-dependent dehydrogenase complexes. In this study, the X-ray structure of BcGDHγα, the catalytic subunit (α-subunit) of BcGDH complexed with a hitchhiker protein (γ-subunit), was determined. The most prominent feature of this enzyme is the presence of the 3Fe–4S cluster, which is located at the surface of the catalytic subunit and functions in intramolecular and intermolecular electron transfer from FAD to the electron-transfer subunit. The structure of the complex revealed that these two molecules are connected through disulfide bonds and hydrophobic interactions, and that the formation of disulfide bonds is required to stabilize the catalytic subunit. The structure of the complex revealed the putative position of the electron-transfer subunit. A comparison of the structures of BcGDHγα and membrane-bound fumarate reductases suggested that the whole BcGDH complex, which also includes the membrane-bound β-subunit containing three heme c moieties, may form a similar overall structure to fumarate reductases, thus accomplishing effective electron transfer.

pH-Dependent Thermal Stability of Vibrio cholerae L-asparaginase

2019 ◽  
Vol 26 (10) ◽  
pp. 743-750 ◽  
Author(s):  
Remya Radha ◽  
Sathyanarayana N. Gummadi
Keyword(s):  
Vibrio Cholerae ◽  
Conformational Changes ◽  
Kinetic Studies ◽  
Structural Features ◽  
Structure Stability ◽  
Kcal Mole ◽  
Scanning Calorimetry ◽  
Wide Range ◽  
Ph Dependent ◽  
Ph Range

Background:pH is one of the decisive macromolecular properties of proteins that significantly affects enzyme structure, stability and reaction rate. Change in pH may protonate or deprotonate the side group of aminoacid residues in the protein, thereby resulting in changes in chemical and structural features. Hence studies on the kinetics of enzyme deactivation by pH are important for assessing the bio-functionality of industrial enzymes. L-asparaginase is one such important enzyme that has potent applications in cancer therapy and food industry.Objective:The objective of the study is to understand and analyze the influence of pH on deactivation and stability of Vibrio cholerae L-asparaginase.Methods:Kinetic studies were conducted to analyze the effect of pH on stability and deactivation of Vibrio cholerae L-asparaginase. Circular Dichroism (CD) and Differential Scanning Calorimetry (DSC) studies have been carried out to understand the pH-dependent conformational changes in the secondary structure of V. cholerae L-asparaginase.Results:The enzyme was found to be least stable at extreme acidic conditions (pH< 4.5) and exhibited a gradual increase in melting temperature from 40 to 81 °C within pH range of 4.0 to 7.0. Thermodynamic properties of protein were estimated and at pH 7.0 the protein exhibited ΔG37of 26.31 kcal mole-1, ΔH of 204.27 kcal mole-1 and ΔS of 574.06 cal mole-1 K-1.Conclusion:The stability and thermodynamic analysis revealed that V. cholerae L-asparaginase was highly stable over a wide range of pH, with the highest stability in the pH range of 5.0–7.0.

Polyoxometalate supported complexes as effective electron-transfer mediators in dye-sensitized solar cells

2014 ◽  
Vol 43 (4) ◽  
pp. 1493-1497 ◽  
Author(s):  
Chun-Chen Yuan ◽  
Shi-Ming Wang ◽  
Wei-Lin Chen ◽  
Lin Liu ◽  
Chao Qin ◽  
...  
Keyword(s):  
Electron Transfer ◽  
Solar Cells ◽  
Dye Sensitized Solar Cells ◽  
Effective Electron ◽  
Dye Sensitized ◽  
Sensitized Solar Cells
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