Characterization of Rhodobacter capsulatus genes encoding a molybdenum transport system and putative molybdenum-pterin-binding proteins.
The alternative, heterometal-free nitrogenase of Rhodobacter capsulatus is repressed by traces of molybdenum in the medium. Strains carrying mutations located downstream of nifB copy II were able to express the alternative nitrogenase even in the presence of high molybdate concentrations. DNA sequence analysis of a 5.5-kb fragment of this region revealed six open reading frames, designated modABCD, mopA, and mopB. The gene products of modB and modC are homologous to ChlJ and ChlD of Escherichia coli and represent an integral membrane protein and an ATP-binding protein typical of high-affinity transport systems, respectively. ModA and ModD exhibited no homology to known proteins, but a leader peptide characteristic of proteins cleaved during export to the periplasm is present in ModA, indicating that ModA might be a periplasmic molybdate-binding protein. The MopA and MopB proteins showed a high degree of amino acid sequence homology to each other. Both proteins contained a tandem repeat of a domain encompassing 70 amino acid residues, which had significant sequence similarity to low-molecular-weight molybdenum-pterin-binding proteins from Clostridium pasteurianum. Compared with that for the parental nifHDK deletion strain, the molybdenum concentrations necessary to repress the alternative nitrogenase were increased 4-fold in a modD mutant and 500-fold in modA, modB, and modC mutants. No significant inhibition of the heterometal-free nitrogenase by molybdate was observed for mopA mopB double mutants. The uptake of molybdenum by mod and mop mutants was estimated by measuring the activity of the conventional molybdenum-containing nitrogenase. Molybdenum transport was not affected in a mopA mopB double mutant, whereas strains carrying lesions in the binding-protein-dependent transport system were impaired in molybdenum uptake.
Wang
G
G
Lehrstuhl für Genetik, Fakultät für Biologie, Universität Bielefeld, Germany.
Angermüller
S
S
Klipp
W
W
D000595:Amino Acid Sequence; D001426:Bacterial Proteins / Q000235:genetics* / Q000378:metabolism; D001483:Base Sequence; D001692:Biological Transport; D002352:Carrier Proteins / Q000235:genetics*; D002874:Chromosome Mapping; D004252:DNA Mutational Analysis; D004305:Dose-Response Relationship, Drug; D004794:Enzyme Repression / Q000187:drug effects; D005798:Genes, Bacterial / Q000235:genetics*; D026901:Membrane Transport Proteins; D008969:Molecular Sequence Data; D008982:Molybdenum / Q000378:metabolism* / Q000494:pharmacology; D009591:Nitrogenase / Q000235:genetics; D011622:Pterins / Q000378:metabolism*; D016354:Rhodobacter capsulatus / Q000235:genetics*; D017422:Sequence Analysis, DNA; D017386:Sequence Homology, Amino Acid
D001426:Bacterial Proteins; D002352:Carrier Proteins; D026901:Membrane Transport Proteins; D011622:Pterins; C081166:mopA protein, Rhodobacter capsulatus; C081167:mopB protein, Rhodobacter capsulatus; C050771:mopI protein, Clostridium pasteurianum; D008982:Molybdenum; D009591:Nitrogenase