title: Characterization of axial and proximal histidine mutations of the decaheme cytochrome MtrA from Shewanella sp. strain ANA-3 and implications for the electron transport system.
abstract: Extracellular respiration of solid-phase electron acceptors in some microorganisms requires a complex chain of multiheme c-type cytochromes that span the inner and outer membranes. In Shewanella species, MtrA, an ~35-kDa periplasmic decaheme c-type cytochrome, is an essential component for extracellular respiration of iron(III). The exact mechanism of electron transport has not yet been resolved, but the arrangement of the polypeptide chain may have a strong influence on the capability of the MtrA cytochrome to transport electrons. The iron hemes of MtrA are bound to its polypeptide chain via proximal (CXXCH) and distal histidine residues. In this study, we show the effects of mutating histidine residues of MtrA to arginine on protein expression and extracellular respiration using Shewanella sp. strain ANA-3 as a model organism. Individual mutations to six out of nine proximal histidines in CXXCH of MtrA led to decreased protein expression. However, distal histidine mutations resulted in various degrees of protein expression. In addition, the effects of histidine mutations on extracellular respiration were tested using ferrihydrite and current production in microbial fuel cells. These results show that proximal histidine mutants were unable to reduce ferrihydrite. Mutations to the distal histidine residues resulted in various degrees of ferrihydrite reduction. These findings indicate that mutations to the proximal histidine residues affect MtrA expression, leading to loss of extracellular respiration ability. In contrast, mutations to the distal histidine residues are less detrimental to protein expression, and extracellular respiration can proceed.
authors.affiliation: Department of Microbiology and Environmental Toxicology, University of California, Santa Cruz, California, USA. creyes6@gmail.com
authors.forename: Carolina
authors.initials: C
authors.lastname: Reyes
authors.forename: Fang
authors.initials: F
authors.lastname: Qian
authors.forename: Alissa
authors.initials: A
authors.lastname: Zhang
authors.forename: Sergey
authors.initials: S
authors.lastname: Bondarev
authors.forename: Angel
authors.initials: A
authors.lastname: Welch
authors.forename: Michael P
authors.initials: MP
authors.lastname: Thelen
authors.forename: Chad W
authors.initials: CW
authors.lastname: Saltikov
mesh_terms: D018528:ATP-Binding Cassette Transporters / Q000235:genetics* / Q000378:metabolism*; D000595:Amino Acid Sequence; D001120:Arginine / Q000235:genetics; D001426:Bacterial Proteins / Q000235:genetics* / Q000378:metabolism*; D004579:Electron Transport; D005290:Ferric Compounds / Q000378:metabolism; D015964:Gene Expression Regulation, Bacterial; D006639:Histidine / Q000235:genetics; D008969:Molecular Sequence Data; D050505:Mutant Proteins / Q000235:genetics / Q000378:metabolism; D020125:Mutation, Missense; D010084:Oxidation-Reduction; D016415:Sequence Alignment; D020592:Shewanella / Q000201:enzymology* / Q000235:genetics / Q000378:metabolism
chemical_list: D018528:ATP-Binding Cassette Transporters; D001426:Bacterial Proteins; D005290:Ferric Compounds; C100938:MtrA protein, Bacteria; D050505:Mutant Proteins; D006639:Histidine; C092844:ferric oxyhydroxide; D001120:Arginine