title: A bacterial process for selenium nanosphere assembly.
abstract: During selenate respiration by Thauera selenatis, the reduction of selenate results in the formation of intracellular selenium (Se) deposits that are ultimately secreted as Se nanospheres of approximately 150 nm in diameter. We report that the Se nanospheres are associated with a protein of approximately 95 kDa. Subsequent experiments to investigate the expression and secretion profile of this protein have demonstrated that it is up-regulated and secreted in response to increasing selenite concentrations. The protein was purified from Se nanospheres, and peptide fragments from a tryptic digest were used to identify the gene in the draft T. selenatis genome. A matched open reading frame was located, encoding a protein with a calculated mass of 94.5 kDa. N-terminal sequence analysis of the mature protein revealed no cleavable signal peptide, suggesting that the protein is exported directly from the cytoplasm. The protein has been called Se factor A (SefA), and homologues of known function have not been reported previously. The sefA gene was cloned and expressed in Escherichia coli, and the recombinant His-tagged SefA purified. In vivo experiments demonstrate that SefA forms larger (approximately 300 nm) Se nanospheres in E. coli when treated with selenite, and these are retained within the cell. In vitro assays demonstrate that the formation of Se nanospheres upon the reduction of selenite by glutathione are stabilized by the presence of SefA. The role of SefA in selenium nanosphere assembly has potential for exploitation in bionanomaterial fabrication.
authors.affiliation: Biosciences, College of Life and Environmental Sciences, University of Exeter, Stocker Road, Exeter EX4 4QD, United Kingdom.
authors.forename: Charles M
authors.initials: CM
authors.lastname: Debieux
authors.forename: Elizabeth J
authors.initials: EJ
authors.lastname: Dridge
authors.forename: Claudia M
authors.initials: CM
authors.lastname: Mueller
authors.forename: Peter
authors.initials: P
authors.lastname: Splatt
authors.forename: Konrad
authors.initials: K
authors.lastname: Paszkiewicz
authors.forename: Iona
authors.initials: I
authors.lastname: Knight
authors.forename: Hannah
authors.initials: H
authors.lastname: Florance
authors.forename: John
authors.initials: J
authors.lastname: Love
authors.forename: Richard W
authors.initials: RW
authors.lastname: Titball
authors.forename: Richard J
authors.initials: RJ
authors.lastname: Lewis
authors.forename: David J
authors.initials: DJ
authors.lastname: Richardson
authors.forename: Clive S
authors.initials: CS
authors.lastname: Butler
mesh_terms: D018407:Bacterial Physiological Phenomena; D001426:Bacterial Proteins / Q000235:genetics / Q000302:isolation & purification / Q000378:metabolism*; D008969:Molecular Sequence Data; D054118:Nanospheres / Q000737:chemistry*; D064586:Selenic Acid; D012643:Selenium / Q000737:chemistry / Q000378:metabolism*; D018036:Selenium Compounds / Q000378:metabolism; D018038:Sodium Selenite / Q000494:pharmacology; D020628:Thauera / Q000737:chemistry* / Q000378:metabolism; D015854:Up-Regulation / Q000187:drug effects / Q000235:genetics
chemical_list: D001426:Bacterial Proteins; D018036:Selenium Compounds; D012643:Selenium; D018038:Sodium Selenite; D064586:Selenic Acid