title: Vibrio cholerae VciB Mediates Iron Reduction.
abstract: Vibrio choleraeis the causative agent of the severe diarrheal disease cholera.V. choleraethrives within the human host, where it replicates to high numbers, but it also persists within the aquatic environments of ocean and brackish water. To survive within these nutritionally diverse environments,V. choleraemust encode the necessary tools to acquire the essential nutrient iron in all forms it may encounter. A prior study of systems involved in iron transport inV. choleraerevealed the existence ofvciB, which, while unable to directly transport iron, stimulates the transport of iron through ferrous (Fe2+) iron transport systems. We demonstrate here a role for VciB inV. choleraein which VciB stimulates the reduction of Fe3+to Fe2+, which can be subsequently transported into the cell with the ferrous iron transporter Feo. Iron reduction is independent of functional iron transport but is associated with the electron transport chain. Comparative analysis of VciB orthologs suggests a similar role for other proteins in the VciB family. Our data indicate that VciB is a dimer located in the inner membrane with three transmembrane segments and a large periplasmic loop. Directed mutagenesis of the protein reveals two highly conserved histidine residues required for function. Taken together, our results support a model whereby VciB reduces ferric iron using energy from the electron transport chain.IMPORTANCEVibrio choleraeis a prolific human pathogen and environmental organism. The acquisition of essential nutrients such as iron is critical for replication, andV. choleraeencodes a number of mechanisms to use iron from diverse environments. Here, we describe theV. choleraeprotein VciB that increases the reduction of oxidized ferric iron (Fe3+) to the ferrous form (Fe2+), thus promoting iron acquisition through ferrous iron transporters. Analysis of VciB orthologs inBurkholderiaandAeromonasspp. suggest that they have a similar activity, allowing a functional assignment for this previously uncharacterized protein family. This study builds upon our understanding of proteins known to mediate iron reduction in bacteria.
authors.affiliation: Department of Molecular Biosciences, The University of Texas, Austin, Texas, USA.
authors.forename: Eric D
authors.initials: ED
authors.lastname: Peng
authors.affiliation: Department of Molecular Biosciences, The University of Texas, Austin, Texas, USA smpayne@austin.utexas.edu.
authors.forename: Shelley M
authors.initials: SM
authors.lastname: Payne
mesh_terms: D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism*; D004252:DNA Mutational Analysis; D005290:Ferric Compounds / Q000378:metabolism*; D005296:Ferrous Compounds / Q000378:metabolism*; D008565:Membrane Proteins / Q000235:genetics / Q000378:metabolism*; D016297:Mutagenesis, Site-Directed; D010084:Oxidation-Reduction; D014734:Vibrio cholerae / Q000201:enzymology* / Q000235:genetics
chemical_list: D001426:Bacterial Proteins; D005290:Ferric Compounds; D005296:Ferrous Compounds; D008565:Membrane Proteins
keywords: Vibrio cholerae; iron acquisition; iron reductase