title: Purification and structural characterization of a flavoprotein induced by iron limitation in Methanobacterium thermoautotrophicum Marburg.
abstract: Cells of Methanobacterium thermoautotrophicum (strain Marburg) grown under iron-limiting conditions were found to synthesize a soluble polypeptide as one of the major cell proteins. This polypeptide purified as a homotetramer (170 kDa [subunit molecular mass, 43 kDa]) had a UV-visible spectrum typical of flavoproteins and contained 0.7 mol of flavin mononucleotide per mol of monomer. Quantitative analysis by immunoblotting with polyclonal antibodies indicated that the flavoprotein, which amounts to about 0.6% of soluble cell protein under iron-sufficient conditions (> or = 50 microM Fe2+), was induced fivefold by iron limitation (< 12 microM Fe2+). The flavoprotein-encoding gene, fprA, was cloned and sequenced. Sequence analysis revealed a well-conserved archaebacterial consensus promoter upstream of fprA, a flavodoxin signature within fprA, and 28% amino acid identity with a putative flavin mononucleotide-containing protein of Rhodobacter capsulatus which is found within an operon involved in nitrogen fixation. A possible physiological function for the flavoprotein is discussed.
authors.affiliation: Mikrobiologisches Institut, Swiss Federal Institute of Technology, Zurich.
authors.forename: A
authors.initials: A
authors.lastname: Wasserfallen
authors.forename: K
authors.initials: K
authors.lastname: Huber
authors.forename: T
authors.initials: T
authors.lastname: Leisinger
mesh_terms: D000595:Amino Acid Sequence; D001105:Archaea / Q000235:genetics; D001425:Bacterial Outer Membrane Proteins / Q000737:chemistry / Q000235:genetics* / Q000302:isolation & purification; D001426:Bacterial Proteins; D001483:Base Sequence; D003001:Cloning, Molecular; D005486:Flavin Mononucleotide / Q000302:isolation & purification*; D015964:Gene Expression Regulation, Bacterial; D005798:Genes, Bacterial / Q000235:genetics; D007501:Iron / Q000378:metabolism*; D033862:Iron-Binding Proteins; D017014:Methanobacterium / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism; D008969:Molecular Sequence Data; D008970:Molecular Weight; D010084:Oxidation-Reduction; D033902:Periplasmic Binding Proteins; D011401:Promoter Regions, Genetic / Q000235:genetics; D011487:Protein Conformation; D016354:Rhodobacter capsulatus / Q000235:genetics; D017422:Sequence Analysis, DNA; D017386:Sequence Homology, Amino Acid; D013053:Spectrophotometry
chemical_list: D001425:Bacterial Outer Membrane Proteins; D001426:Bacterial Proteins; D033862:Iron-Binding Proteins; D033902:Periplasmic Binding Proteins; D005486:Flavin Mononucleotide; D007501:Iron