scholarly journals Structural modeling of an outer membrane electron conduit from a metal-reducing bacterium suggests electron transfer via periplasmic redox partners

2018 ◽  
Vol 293 (21) ◽  
pp. 8103-8112 ◽  
Author(s):  
Marcus J. Edwards ◽  
Gaye F. White ◽  
Colin W. Lockwood ◽  
Matthew C. Lawes ◽  
Anne Martel ◽  
...  
Keyword(s):  
Electron Transfer ◽  
Outer Membrane ◽  
Membrane Surface ◽  
Shewanella Oneidensis ◽  
Direct Interaction ◽  
Electron Acceptors ◽  
Scattering Data ◽  
Redox Partners ◽  
Mediated Electron Transfer ◽  
Tetraheme Cytochrome

Many subsurface microorganisms couple their metabolism to the reduction or oxidation of extracellular substrates. For example, anaerobic mineral-respiring bacteria can use external metal oxides as terminal electron acceptors during respiration. Porin–cytochrome complexes facilitate the movement of electrons generated through intracellular catabolic processes across the bacterial outer membrane to these terminal electron acceptors. In the mineral-reducing model bacterium Shewanella oneidensis MR-1, this complex is composed of two decaheme cytochromes (MtrA and MtrC) and an outer-membrane β-barrel (MtrB). However, the structures and mechanisms by which porin–cytochrome complexes transfer electrons are unknown. Here, we used small-angle neutron scattering (SANS) to study the molecular structure of the transmembrane complexes MtrAB and MtrCAB. Ab initio modeling of the scattering data yielded a molecular envelope with dimensions of ∼105 × 60 × 35 Å for MtrAB and ∼170 × 60 × 45 Å for MtrCAB. The shapes of these molecular envelopes suggested that MtrC interacts with the surface of MtrAB, extending ∼70 Å from the membrane surface and allowing the terminal hemes to interact with both MtrAB and an extracellular acceptor. The data also reveal that MtrA fully extends through the length of MtrB, with ∼30 Å being exposed into the periplasm. Proteoliposome models containing membrane-associated MtrCAB and internalized small tetraheme cytochrome (STC) indicate that MtrCAB could reduce Fe(III) citrate with STC as an electron donor, disclosing a direct interaction between MtrCAB and STC. Taken together, both structural and proteoliposome experiments support porin–cytochrome–mediated electron transfer via periplasmic cytochromes such as STC.

scholarly journals Bespoke Biomolecular Wires for Transmembrane Electron Transfer: Spontaneous Assembly of a Functionalized Multiheme Electron Conduit

2021 ◽  
Vol 12 ◽  
Author(s):  
Samuel E. H. Piper ◽  
Marcus J. Edwards ◽  
Jessica H. van Wonderen ◽  
Carla Casadevall ◽  
Anne Martel ◽  
...  
Keyword(s):  
Electron Transfer ◽  
Outer Membrane ◽  
Lipid Bilayer ◽  
Microbial Fuel Cells ◽  
Shewanella Oneidensis ◽  
Membrane Lipid ◽  
Electron Transfer Pathway ◽  
Redox Partners ◽  
Membrane Lipid Bilayer

Shewanella oneidensis exchanges electrons between cellular metabolism and external redox partners in a process that attracts much attention for production of green electricity (microbial fuel cells) and chemicals (microbial electrosynthesis). A critical component of this pathway is the outer membrane spanning MTR complex, a biomolecular wire formed of the MtrA, MtrB, and MtrC proteins. MtrA and MtrC are decaheme cytochromes that form a chain of close-packed hemes to define an electron transfer pathway of 185 Å. MtrA is wrapped inside MtrB for solubility across the outer membrane lipid bilayer; MtrC sits outside the cell for electron exchange with external redox partners. Here, we demonstrate tight and spontaneous in vitro association of MtrAB with separately purified MtrC. The resulting complex is comparable with the MTR complex naturally assembled by Shewanella in terms of both its structure and rates of electron transfer across a lipid bilayer. Our findings reveal the potential for building bespoke electron conduits where MtrAB combines with chemically modified MtrC, in this case, labeled with a Ru-dye that enables light-triggered electron injection into the MtrC heme chain.

scholarly journals Mind the gap: diversity and reactivity relationships among multihaem cytochromes of the MtrA/DmsE family

2012 ◽  
Vol 40 (6) ◽  
pp. 1268-1273 ◽  
Author(s):  
Kathryn D. Bewley ◽  
Mackenzie A. Firer-Sherwood ◽  
Jee-Young Mock ◽  
Nozomi Ando ◽  
Catherine L. Drennan ◽  
...  
Keyword(s):  
Electron Transfer ◽  
Membrane Proteins ◽  
Outer Membrane ◽  
Outer Membrane Proteins ◽  
Evolutionary Relationship ◽  
Shewanella Oneidensis ◽  
Anaerobic Respiration ◽  
Electron Acceptors ◽  
Protein Film ◽  
Protein Film Voltammetry

Shewanella oneidensis MR-1 has the ability to use many external terminal electron acceptors during anaerobic respiration, such as DMSO. The pathway that facilitates this electron transfer includes the decahaem cytochrome DmsE, a paralogue of the MtrA family of decahaem cytochromes. Although both DmsE and MtrA are decahaem cytochromes implicated in the long-range electron transfer across a ~300 Å (1 Å=0.1 nm) wide periplasmic ‘gap’, MtrA has been shown to be only 105 Å in maximal length. In the present paper, DmsE is further characterized via protein film voltammetry, revealing that the electrochemistry of the DmsE haem cofactors display macroscopic potentials lower than those of MtrA by 100 mV. It is possible this tuning of the redox potential of DmsE is required to shuttle electrons to the outer-membrane proteins specific to DMSO reduction. Other decahaem cytochromes found in S. oneidensis, such as the outer-membrane proteins MtrC, MtrF and OmcA, have been shown to have electrochemical properties similar to those of MtrA, yet possess a different evolutionary relationship.

scholarly journals Development of a proteoliposome model to probe transmembrane electron-transfer reactions

2012 ◽  
Vol 40 (6) ◽  
pp. 1257-1260 ◽  
Author(s):  
Gaye F. White ◽  
Zhi Shi ◽  
Liang Shi ◽  
Alice C. Dohnalkova ◽  
James K. Fredrickson ◽  
...  
Keyword(s):  
Electron Transfer ◽  
Outer Membrane ◽  
Protein Complex ◽  
Methyl Viologen ◽  
Cation Exchanger ◽  
Shewanella Oneidensis ◽  
Model System ◽  
Electron Acceptors ◽  
Transfer Reactions ◽  
Electron Carrier

The mineral-respiring bacterium Shewanella oneidensis uses a protein complex, MtrCAB, composed of two decahaem cytochromes brought together inside a transmembrane porin to transport electrons across the outer membrane to a variety of mineral-based electron acceptors. A proteoliposome system has been developed that contains Methyl Viologen as an internalized electron carrier and valinomycin as a membrane-associated cation exchanger. These proteoliposomes can be used as a model system to investigate MtrCAB function.

scholarly journals A directional electron transfer regulator based on heme-chain architecture in the small tetraheme cytochrome c from Shewanella oneidensis

FEBS Letters ◽  
2002 ◽  
Vol 532 (3) ◽  
pp. 333-337 ◽  
Author(s):  
Erisa Harada ◽  
Jiro Kumagai ◽  
Kiyoshi Ozawa ◽  
Shinichiro Imabayashi ◽  
Alexandre S Tsapin ◽  
...  
Keyword(s):  
Electron Transfer ◽  
Cytochrome C ◽  
Shewanella Oneidensis ◽  
Chain Architecture ◽  
Tetraheme Cytochrome ◽  
Small Tetraheme Cytochrome

The membrane-bound tetrahaem c-type cytochrome CymA interacts directly with the soluble fumarate reductase in Shewanella

2002 ◽  
Vol 30 (4) ◽  
pp. 658-662 ◽  
Author(s):  
C. Schwalb ◽  
S. K. Chapman ◽  
G. A. Reid
Keyword(s):  
Electron Transfer ◽  
Outer Membrane ◽  
Shewanella Oneidensis ◽  
Anaerobic Respiration ◽  
Fumarate Reductase ◽  
Sulphur Compounds ◽  
Sequence Alignments ◽  
Membrane Bound ◽  
Periplasmic Domain

Shewanella spp. demonstrate great variability in the use of terminal electron acceptors in anaerobic respiration; these include nitrate, fumarate, DMSO, trimethylamine oxide, sulphur compounds and metal oxides. These pathways open up possible applications in bioremediation. The wide variety of respiratory substrates for Shewanella is correlated with the evolution of several multi-haem membrane-bound, periplasmic and outer-membrane c-type cytochromes. The 21 kDa c-type cytochrome CymA of the freshwater strain Shewanella oneidensis MR-1 has an N-terminal membrane anchor and a globular tetrahaem periplasmic domain. According to sequence alignments, CymA is a member of the NapC/NirT family. This family of redox proteins is responsible for electron transfer from the quinone pool to periplasmic and outer-membrane-bound reductases. Prior investigations have shown that the absence of CymA results in loss of the ability to respire with Fe(III), fumarate and nitrate, indicating that CymA is involved in electron transfer to several terminal reductases. Here we describe the expression, purification and characterization of a soluble, truncated CymA (‘CymA). Potentiometric studies suggest that there are two pairs of haems with potentials of -175 and -261 mV and that ‘CymA is an efficient electron donor for the soluble fumarate reductase, flavocytochrome c3.

scholarly journals Genomic Plasticity Enables a Secondary Electron Transport Pathway in Shewanella oneidensis

2012 ◽  
Vol 79 (4) ◽  
pp. 1150-1159 ◽  
Author(s):  
M. Schicklberger ◽  
G. Sturm ◽  
J. Gescher
Keyword(s):  
Electron Transfer ◽  
Cell Surface ◽  
Outer Membrane ◽  
Iron Reduction ◽  
Shewanella Oneidensis ◽  
Transport Pathway ◽  
Content Type ◽  
Reducing Conditions ◽  
Dissimilatory Iron Reduction ◽  
Membrane Spanning

ABSTRACTMicrobial dissimilatory iron reduction is an important biogeochemical process. It is physiologically challenging because iron occurs in soils and sediments in the form of insoluble minerals such as hematite or ferrihydrite.Shewanella oneidensisMR-1 evolved an extended respiratory chain to the cell surface to reduce iron minerals. Interestingly, the organism evolved a similar strategy for reduction of dimethyl sulfoxide (DMSO), which is reduced at the cell surface as well. It has already been established that electron transfer through the outer membrane is accomplished via a complex in which β-barrel proteins enable interprotein electron transfer between periplasmic oxidoreductases and cell surface-localized terminal reductases. MtrB is the β-barrel protein that is necessary for dissimilatory iron reduction. It forms a complex together with the periplasmic decahemec-type cytochrome MtrA and the outer membrane decahemec-type cytochrome MtrC. Consequently,mtrBdeletion mutants are unable to reduce ferric iron. The data presented here show that this inability can be overcome by a mobile genomic element with the ability to activate the expression of downstream genes and which is inserted within the SO4362 gene of the SO4362-to-SO4357 gene cluster. This cluster carries genes similar tomtrAandmtrBand encoding a putative cell surface DMSO reductase. Expression of SO4359 and SO4360 alone was sufficient to complement not only anmtrBmutant under ferric citrate-reducing conditions but also a mutant that furthermore lacks any outer membrane cytochromes. Hence, the putative complex formed by the SO4359 and SO4360 gene products is capable not only of membrane-spanning electron transfer but also of reducing extracellular electron acceptors.

scholarly journals Regulation of Gene Expression in Shewanella oneidensis MR-1 during Electron Acceptor Limitation and Bacterial Nanowire Formation

2016 ◽  
Vol 82 (17) ◽  
pp. 5428-5443 ◽  
Author(s):  
Sarah E. Barchinger ◽  
Sahand Pirbadian ◽  
Christine Sambles ◽  
Carol S. Baker ◽  
Kar Man Leung ◽  
...  
Keyword(s):  
Gene Expression ◽  
Electron Transfer ◽  
Outer Membrane ◽  
Electron Acceptor ◽  
Shewanella Oneidensis ◽  
Oxygen Limitation ◽  
Extracellular Electron Transfer ◽  
Transport Pathways ◽  
Content Type ◽  
Genes Encoding

ABSTRACTIn limiting oxygen as an electron acceptor, the dissimilatory metal-reducing bacteriumShewanella oneidensisMR-1 rapidly forms nanowires, extensions of its outer membrane containing the cytochromes MtrC and OmcA needed for extracellular electron transfer. RNA sequencing (RNA-Seq) analysis was employed to determine differential gene expression over time from triplicate chemostat cultures that were limited for oxygen. We identified 465 genes with decreased expression and 677 genes with increased expression. The coordinated increased expression of heme biosynthesis, cytochrome maturation, and transport pathways indicates thatS. oneidensisMR-1 increases cytochrome production, including the transcription of genes encoding MtrA, MtrC, and OmcA, and transports these decaheme cytochromes across the cytoplasmic membrane during electron acceptor limitation and nanowire formation. In contrast, the expression of themtrAandmtrChomologsmtrFandmtrDeither remains unaffected or decreases under these conditions. TheompWgene, encoding a small outer membrane porin, has 40-fold higher expression during oxygen limitation, and it is proposed that OmpW plays a role in cation transport to maintain electrical neutrality during electron transfer. The genes encoding the anaerobic respiration regulator cyclic AMP receptor protein (CRP) and the extracytoplasmic function sigma factor RpoE are among the transcription factor genes with increased expression. RpoE might function by signaling the initial response to oxygen limitation. Our results show that RpoE activates transcription from promoters upstream ofmtrCandomcA. The transcriptome and mutant analyses ofS. oneidensisMR-1 nanowire production are consistent with independent regulatory mechanisms for extending the outer membrane into tubular structures and for ensuring the electron transfer function of the nanowires.IMPORTANCEShewanella oneidensisMR-1 has the capacity to transfer electrons to its external surface using extensions of the outer membrane called bacterial nanowires. These bacterial nanowires link the cell's respiratory chain to external surfaces, including oxidized metals important in bioremediation, and explain whyS. oneidensiscan be utilized as a component of microbial fuel cells, a form of renewable energy. In this work, we use differential gene expression analysis to focus on which genes function to produce the nanowires and promote extracellular electron transfer during oxygen limitation. Among the genes that are expressed at high levels are those encoding cytochrome proteins necessary for electron transfer.Shewanellacoordinates the increased expression of regulators, metabolic pathways, and transport pathways to ensure that cytochromes efficiently transfer electrons along the nanowires.

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