Structural modeling of an outer membrane electron conduit from a metal-reducing bacterium suggests electron transfer via periplasmic redox partners.
J Biol Chem
; 293(21): 8103-8112, 2018 05 25.
Article
em En
| MEDLINE
| ID: mdl-29636412
ABSTRACT
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 ß-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 â¼105 × 60 × 35 Å for MtrAB and â¼170 × 60 × 45 Å for MtrCAB. The shapes of these molecular envelopes suggested that MtrC interacts with the surface of MtrAB, extending â¼70 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 â¼30 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.
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MEDLINE
Assunto principal:
Proteínas da Membrana Bacteriana Externa
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Proteínas de Bactérias
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Membrana Celular
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Transportadores de Cassetes de Ligação de ATP
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Periplasma
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Shewanella
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Grupo dos Citocromos c
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Elétrons
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Metais
Idioma:
En
Ano de publicação:
2018
Tipo de documento:
Article