scholarly journals A regulatory livR mutation affecting high- and low-affinity transport systems for branched-chain amino acids in Salmonella typhimurium.

1983 ◽  
Vol 58 (2) ◽  
pp. 107-119 ◽  
Author(s):  
Kuniharu OHNISHI ◽  
Keiko MURATA-MATSUBARA ◽  
Kazuyoshi KIRITANI
Keyword(s):  
Amino Acids ◽  
Salmonella Typhimurium ◽  
Branched Chain Amino Acids ◽  
Transport Systems ◽  
Branched Chain

scholarly journals YjeH Is a Novel Exporter of l-Methionine and Branched-Chain Amino Acids in Escherichia coli

2015 ◽  
Vol 81 (22) ◽  
pp. 7753-7766 ◽  
Author(s):  
Qian Liu ◽  
Yong Liang ◽  
Yun Zhang ◽  
Xiuling Shang ◽  
Shuwen Liu ◽  
...  
Keyword(s):  
Escherichia Coli ◽  
Amino Acids ◽  
Amino Acid ◽  
Fluorescent Protein ◽  
Branched Chain Amino Acids ◽  
Transport Systems ◽  
Content Type ◽  
Overexpression Strain ◽  
Branched Chain ◽  
Amino Acid Efflux

ABSTRACTAmino acid efflux transport systems have important physiological functions and play vital roles in the fermentative production of amino acids. However, no methionine exporter has yet been identified inEscherichia coli. In this study, we identified a novel amino acid exporter, YjeH, inE. coli. TheyjeHoverexpression strain exhibited high tolerance to the structural analogues ofl-methionine and branched-chain amino acids, decreased intracellular amino acid levels, and enhanced export rates in the presence of a Met-Met, Leu-Leu, Ile-Ile, or Val-Val dipeptide, suggesting that YjeH functions as an exporter ofl-methionine and the three branched-chain amino acids. The export of the four amino acids in theyjeHoverexpression strain was competitively inhibited in relation to each other. The expression ofyjeHwas strongly induced by increasing cytoplasmic concentrations of substrate amino acids. Green fluorescent protein (GFP)-tagged YjeH was visualized by total internal reflection fluorescence microscopy to confirm the plasma membrane localization of YjeH. Phylogenetic analysis of transporters indicated that YjeH belongs to the amino acid efflux family of the amino acid/polyamine/organocation (APC) superfamily. Structural modeling revealed that YjeH has the typical “5 + 5” transmembrane α-helical segment (TMS) inverted-repeat fold of APC superfamily transporters, and its binding sites are strictly conserved. The enhanced capacity ofl-methionine export by the overexpression ofyjeHin anl-methionine-producing strain resulted in a 70% improvement in titer. This study supplements the transporter classification and provides a substantial basis for the application of the methionine exporter in metabolic engineering.

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