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The Putative outer membrane beta-barrel porin (MtrB_PioB) Family [Function: Non-specific diffusion channels] Seed alignment | Full alignment | Pfam page | TC-DB page

MtrB-PioB is a family of bacterial putative outer membrane porins. This family, is secreted as part of the pio (phototrophic iron oxidation) operon that has been found to couple the oxidation of ferrous iron [Fe(II)] to reductive CO2 fixation using light energy. PioABC is found in Rhodopseudomonas palustris and MtrB-PioB is likely to be a ß-barrel porin. Similar to other outer membrane porins, PioB and MtrB are predicted to have long loops protruding into the extracellular space and short turns on the periplasmic side. The Gram-negative Shewanella is one of the most studied bacterial genera capable of transferring electrons out of the cell to solid-phase Fe(III) and Mn(IV) minerals in order to support anaerobic respiration. The icosaheme protein complex comprising three subunits (MtrA, MtrB, MtrC) from the outer membrane of Shewanella oneidensis and shown that this Mtr complex is able to conduct electrons bidirectionally across proteoliposome bilayers sustaining electron transport rates over 8,500 e s1. MtrAB is proposed to span the outer membrane and provide electrical connection between the catabolic electron transfer network within the cell, and the electron dispersing MtrC outside the cell. The crystal structure reveals a heterotrimeric complex that consists of two cytochromes, MtrC and MtrA, and a 26 strand ß-barrel protein, MtrB, that sheathes and insulates MtrA.

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Literature references

Goethite Reduction by a Neutrophilic Member of the Alphaproteobacterial Genus Telmatospirillum
Front Microbiol. 2019 Dec 20;10:2938. doi: 10.3389/fmicb.2019.02938. eCollection 2019.
PMID: 31921089

Photoferrotrophs Produce a PioAB Electron Conduit for Extracellular Electron Uptake
mBio. 2019 Nov 5;10(6):e02668-19. doi: 10.1128/mBio.02668-19.
PMID: 31690680

Structures of nitroaromatic compounds induce Shewanella oneidensis MR-1 to adopt different electron transport pathways to reduce the contaminants
J Hazard Mater. 2020 Feb 15;384:121495. doi: 10.1016/j.jhazmat.2019.121495. Epub 2019 Oct 21.
PMID: 31704119

Metal Reduction and Protein Secretion Genes Required for Iodate Reduction by Shewanella oneidensis
Appl Environ Microbiol. 2019 Jan 23;85(3):e02115-18. doi: 10.1128/AEM.02115-18. Print 2019 Feb 1.
PMID: 30446562

Structural modeling of an outer membrane electron conduit from a metal-reducing bacterium suggests electron transfer via periplasmic redox partners
J Biol Chem. 2018 May 25;293(21):8103-8112. doi: 10.1074/jbc.RA118.001850. Epub 2018 Apr 10.
PMID: 29636412

Transcriptional mechanisms for differential expression of outer membrane cytochrome genes omcA and mtrC in Shewanella oneidensis MR-1
BMC Microbiol. 2015 Mar 21;15:68. doi: 10.1186/s12866-015-0406-8.
PMID: 25886963

Rapid electron exchange between surface-exposed bacterial cytochromes and Fe(III) minerals
Proc Natl Acad Sci U S A. 2013 Apr 16;110(16):6346-51. doi: 10.1073/pnas.1220074110. Epub 2013 Mar 28.
PMID: 23538304

Proof of principle for an engineered microbial biosensor based on Shewanella oneidensis outer membrane protein complexes
Biosens Bioelectron. 2013 Sep 15;47:285-91. doi: 10.1016/j.bios.2013.03.010. Epub 2013 Mar 22.
PMID: 23584391

Genomic plasticity enables a secondary electron transport pathway in Shewanella oneidensis
Appl Environ Microbiol. 2013 Feb;79(4):1150-9. doi: 10.1128/AEM.03556-12. Epub 2012 Dec 7.
PMID: 23220953

Mtr extracellular electron-transfer pathways in Fe(III)-reducing or Fe(II)-oxidizing bacteria: a genomic perspective
Biochem Soc Trans. 2012 Dec 1;40(6):1261-7. doi: 10.1042/BST20120098.
PMID: 23176465

Outer-membrane cytochrome-independent reduction of extracellular electron acceptors in Shewanella oneidensis
Microbiology (Reading). 2012 Aug;158(Pt 8):2144-2157. doi: 10.1099/mic.0.058404-0. Epub 2012 Apr 5.
PMID: 22493303

Reconstruction of Extracellular Respiratory Pathways for Iron(III) Reduction in Shewanella Oneidensis Strain MR-1
Front Microbiol. 2012 Feb 21;3:56. doi: 10.3389/fmicb.2012.00056. eCollection 2012.
PMID: 22363330

Molecular Underpinnings of Fe(III) Oxide Reduction by Shewanella Oneidensis MR-1
Front Microbiol. 2012 Feb 15;3:50. doi: 10.3389/fmicb.2012.00050. eCollection 2012.
PMID: 22363328

Involvement of the Shewanella oneidensis decaheme cytochrome MtrA in the periplasmic stability of the beta-barrel protein MtrB
Appl Environ Microbiol. 2011 Feb;77(4):1520-3. doi: 10.1128/AEM.01201-10. Epub 2010 Dec 17.
PMID: 21169449

The pio operon is essential for phototrophic Fe(II) oxidation in Rhodopseudomonas palustris TIE-1
J Bacteriol. 2007 Mar;189(5):1765-73. doi: 10.1128/JB.00776-06. Epub 2006 Dec 22.
PMID: 17189359

Shewanella putrefaciens mtrB encodes an outer membrane protein required for Fe(III) and Mn(IV) reduction
J Bacteriol. 1998 Dec;180(23):6292-7.
PMID: 9829939

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