Isolation of the braZ gene encoding the carrier for a novel branched-chain amino acid transport system in Pseudomonas aeruginosa PAO.
The braZ gene for a novel branched-chain amino acid transport system in Pseudomonas aeruginosa PAO was isolated and characterized. Determination of the nucleotide sequence showed that the braZ gene comprises 1,311 nucleotides specifying a protein of 437 amino acids. Hydropathy analysis suggested that the product is an integral membrane protein with 12 membrane-spanning segments. The amino acid sequence showed extensive homology to those of the braB and brnQ gene products, branched-chain amino acid carriers of P. aeruginosa and Salmonella typhimurium, respectively. By using the T7 RNA polymerase-promoter system, the braZ gene product was identified as a protein of an apparent Mr of 34,000 on a sodium dodecyl sulfate-polyacrylamide gel. Properties of the transport system encoded by braZ were studied by using P. aeruginosa PAO3537, defective in both the high- and low-affinity branched-chain amino acid transport systems (LIV-I and LIV-II, respectively). The transport system encoded by braZ was found to be another effective branched-chain amino acid transport system in P. aeruginosa PAO and was thus designated as LIV-III. This system is specific for isoleucine and valine, giving the same Km value of 12 microM for these amino acids. The system was found, however, to have a very low affinity for leucine, with a Km value of 150 microM, which contrasts with the substrate specificities of LIV-I and LIV-II.
Hoshino
T
T
Mitsubishi Kasei Institute of Life Sciences, Tokyo, Japan.
Kose-Terai
K
K
Uratani
Y
Y
D000595:Amino Acid Sequence; D000597:Amino Acids, Branched-Chain / Q000378:metabolism*; D001426:Bacterial Proteins / Q000235:genetics* / Q000378:metabolism; D001483:Base Sequence; D003001:Cloning, Molecular; D005798:Genes, Bacterial; D007532:Isoleucine / Q000378:metabolism; D007700:Kinetics; D007930:Leucine / Q000378:metabolism; D008565:Membrane Proteins / Q000235:genetics*; D026901:Membrane Transport Proteins; D008969:Molecular Sequence Data; D011550:Pseudomonas aeruginosa / Q000235:genetics*; D014633:Valine / Q000378:metabolism
D000597:Amino Acids, Branched-Chain; D001426:Bacterial Proteins; D008565:Membrane Proteins; D026901:Membrane Transport Proteins; D007532:Isoleucine; C067810:BraZ protein, Pseudomonas aeruginosa; D007930:Leucine; D014633:Valine