Substrate-binding lipoprotein of the cyanobacterium Synechococcus sp. strain PCC 7942 involved in the transport of nitrate and nitrite.
Of the four genes (nrtABCD) required for active transport of nitrate in the cyanobacterium Synechococcus sp. strain PCC 7942, nrtBCD encode membrane components of an ATP-binding cassette transporter involved in the transport of nitrite as well as of nitrate, whereas nrtA encodes a 45-kDa cytoplasmic membrane protein, the biochemical function of which remains unclear. Characterization of the nrtA deletional mutants showed that the 45-kDa protein is essential for the functioning of the nitrate/nitrite transporter. A truncated NrtA protein lacking the N-terminal 81 amino acids, expressed in Escherichia coli cells as a histidine-tagged soluble protein, was shown to bind nitrate and nitrite with high affinity (Kd = 0.3 microM). Immunoblotting analysis using the antibody against the 45-kDa protein revealed a 48-kDa precursor of the protein, which accumulated in the cyanobacterial cells treated with globomycin, an antibiotic that specifically inhibits cleavage of the signal peptide of lipoprotein precursors. These findings indicated that the nrtA gene product is a nitrate- and nitrite-binding lipoprotein. The N-terminal sequences of putative cyanobacterial substrate-binding proteins suggested that lipoprotein modification of substrate-binding proteins of ATP-binding cassette transporters is common in cyanobacteria.
Maeda
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S
Department of Applied Biological Sciences, School of Agricultural Sciences, Nagoya University, Nagoya 464-01, Japan.
Omata
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T
D000595:Amino Acid Sequence; D027321:Anion Transport Proteins; D001426:Bacterial Proteins / Q000096:biosynthesis / Q000737:chemistry / Q000378:metabolism*; D002352:Carrier Proteins / Q000096:biosynthesis / Q000737:chemistry / Q000378:metabolism*; D003001:Cloning, Molecular; D000458:Cyanobacteria / Q000187:drug effects / Q000235:genetics / Q000378:metabolism*; D004926:Escherichia coli; D007700:Kinetics; D008074:Lipoproteins / Q000096:biosynthesis / Q000737:chemistry / Q000378:metabolism*; D008565:Membrane Proteins / Q000096:biosynthesis / Q000737:chemistry / Q000378:metabolism*; D008969:Molecular Sequence Data; D016296:Mutagenesis; D000091285:Nitrate Transporters; D009566:Nitrates / Q000378:metabolism*; D009573:Nitrites / Q000378:metabolism*; D021382:Protein Sorting Signals / Q000737:chemistry / Q000378:metabolism; D011994:Recombinant Proteins / Q000378:metabolism; D017384:Sequence Deletion; D017386:Sequence Homology, Amino Acid; D016324:Sequence Tagged Sites
D027321:Anion Transport Proteins; D001426:Bacterial Proteins; D002352:Carrier Proteins; D008074:Lipoproteins; D008565:Membrane Proteins; D000091285:Nitrate Transporters; D009566:Nitrates; D009573:Nitrites; D021382:Protein Sorting Signals; D011994:Recombinant Proteins