title: Characterization of an electron conduit between bacteria and the extracellular environment.
abstract: A number of species of Gram-negative bacteria can use insoluble minerals of Fe(III) and Mn(IV) as extracellular respiratory electron acceptors. In some species of Shewanella, deca-heme electron transfer proteins lie at the extracellular face of the outer membrane (OM), where they can interact with insoluble substrates. To reduce extracellular substrates, these redox proteins must be charged by the inner membrane/periplasmic electron transfer system. Here, we present a spectro-potentiometric characterization of a trans-OM icosa-heme complex, MtrCAB, and demonstrate its capacity to move electrons across a lipid bilayer after incorporation into proteoliposomes. We also show that a stable MtrAB subcomplex can assemble in the absence of MtrC; an MtrBC subcomplex is not assembled in the absence of MtrA; and MtrA is only associated to the membrane in cells when MtrB is present. We propose a model for the modular organization of the MtrCAB complex in which MtrC is an extracellular element that mediates electron transfer to extracellular substrates and MtrB is a trans-OM spanning beta-barrel protein that serves as a sheath, within which MtrA and MtrC exchange electrons. We have identified the MtrAB module in a range of bacterial phyla, suggesting that it is widely used in electron exchange with the extracellular environment.
authors.affiliation: School of Biological Sciences, University of East Anglia, Norwich NR4 7TJ, United Kingdom.
authors.forename: Robert S
authors.initials: RS
authors.lastname: Hartshorne
authors.forename: Catherine L
authors.initials: CL
authors.lastname: Reardon
authors.forename: Daniel
authors.initials: D
authors.lastname: Ross
authors.forename: Jochen
authors.initials: J
authors.lastname: Nuester
authors.forename: Thomas A
authors.initials: TA
authors.lastname: Clarke
authors.forename: Andrew J
authors.initials: AJ
authors.lastname: Gates
authors.forename: Paul C
authors.initials: PC
authors.lastname: Mills
authors.forename: Jim K
authors.initials: JK
authors.lastname: Fredrickson
authors.forename: John M
authors.initials: JM
authors.lastname: Zachara
authors.forename: Liang
authors.initials: L
authors.lastname: Shi
authors.forename: Alex S
authors.initials: AS
authors.lastname: Beliaev
authors.forename: Matthew J
authors.initials: MJ
authors.lastname: Marshall
authors.forename: Ming
authors.initials: M
authors.lastname: Tien
authors.forename: Susan
authors.initials: S
authors.lastname: Brantley
authors.forename: Julea N
authors.initials: JN
authors.lastname: Butt
authors.forename: David J
authors.initials: DJ
authors.lastname: Richardson
mesh_terms: D018528:ATP-Binding Cassette Transporters / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D001425:Bacterial Outer Membrane Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D001426:Bacterial Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D003574:Cytochrome c Group / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D004579:Electron Transport; D017353:Gene Deletion; D005798:Genes, Bacterial; D007501:Iron / Q000378:metabolism; D007700:Kinetics; D008345:Manganese / Q000378:metabolism; D008823:Micelles; D008954:Models, Biological; D046912:Multiprotein Complexes; D010084:Oxidation-Reduction; D010802:Phylogeny; D054730:Protein Interaction Domains and Motifs; D011510:Proteolipids; D020592:Shewanella / Q000235:genetics / Q000378:metabolism*; D013816:Thermodynamics
chemical_list: D018528:ATP-Binding Cassette Transporters; D001425:Bacterial Outer Membrane Proteins; D001426:Bacterial Proteins; D003574:Cytochrome c Group; D008823:Micelles; C100938:MtrA protein, Bacteria; C116147:MtrB protein, Shewanella putrefaciens; D046912:Multiprotein Complexes; D011510:Proteolipids; C020485:proteoliposomes; D008345:Manganese; D007501:Iron; C433527:MtrC protein, Shewanella