title: Characterization of the arsenate respiratory reductase from Shewanella sp. strain ANA-3.
abstract: Microbial arsenate respiration contributes to the mobilization of arsenic from the solid to the soluble phase in various locales worldwide. To begin to predict the extent to which As(V) respiration impacts arsenic geochemical cycling, we characterized the expression and activity of the Shewanella sp. strain ANA-3 arsenate respiratory reductase (ARR), the key enzyme involved in this metabolism. ARR is expressed at the beginning of the exponential phase and persists throughout the stationary phase, at which point it is released from the cell. In intact cells, the enzyme localizes to the periplasm. To purify ARR, a heterologous expression system was developed in Escherichia coli. ARR requires anaerobic conditions and molybdenum for activity. ARR is a heterodimer of approximately 131 kDa, composed of one ArrA subunit (approximately 95 kDa) and one ArrB subunit (approximately 27 kDa). For ARR to be functional, the two subunits must be expressed together. Elemental analysis of pure protein indicates that one Mo atom, four S atoms associated with a bis-molybdopterin guanine dinucleotide cofactor, and four to five [4Fe-4S] are present per ARR. ARR has an apparent melting temperature of 41 degrees C, a Km of 5 microM, and a Vmax of 11,111 micromol of As(V) reduced min(-1) mg of protein(-1) and shows no activity in the presence of alternative electron acceptors such as antimonite, nitrate, selenate, and sulfate. The development of a heterologous overexpression system for ARR will facilitate future structural and/or functional studies of this protein family.
authors.affiliation: Division of Biology, Howard Hughes Medical Institute, California Institute of Technology, 1200 E. California Blvd, Mail Code 100-23, Pasadena, California 91125, USA.
authors.forename: Davin
authors.initials: D
authors.lastname: Malasarn
authors.forename: Jennifer R
authors.initials: JR
authors.lastname: Keeffe
authors.forename: Dianne K
authors.initials: DK
authors.lastname: Newman
mesh_terms: D053502:Arsenate Reductases / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D001426:Bacterial Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D002462:Cell Membrane / Q000201:enzymology; D017931:DNA Primers; D015964:Gene Expression Regulation, Bacterial; D005822:Genetic Vectors; D007700:Kinetics; D008565:Membrane Proteins / Q000235:genetics / Q000378:metabolism; D010957:Plasmids; D016133:Polymerase Chain Reaction; D021122:Protein Subunits / Q000378:metabolism; D011994:Recombinant Proteins / Q000378:metabolism; D020592:Shewanella / Q000201:enzymology* / Q000235:genetics
chemical_list: D001426:Bacterial Proteins; D017931:DNA Primers; D008565:Membrane Proteins; D021122:Protein Subunits; D011994:Recombinant Proteins; D053502:Arsenate Reductases