L-Lysine Transport

Biosynthesis of the amino acid L-lysine is costly for the cell in terms of energy and reduction equivalents. If present in the medium, L-lysine is imported into C. glutamicum by the uptake system Lysl [37]. Surprisingly, L-lysine is also exported out of the C. glutamicum cell by an active transport system [38-40]. The L-lysine export system LysE excretes L-lysine with a Michaelis-Menten constant (Kj j) value of about 20 mM [41]. Since L-lysine biosynthesis is tightly regulated and C. glutamicum cannot catabolize L-lysine, L-lysine accumulates only under conditions of an unbalanced catabolism. 

This may arise, for example, when a dipeptide containing L-lysine and a catabo-lizable amino acid such as L-alanine is taken up and hydrolyzed by constitutive di- and oligopeptide uptake and hydrolase systems [39, 40]. Synthesis of LysE is controlled by LysG and occurs only if the intracellular L-lysine concentrations exceeds a threshold of about 35 mM [42]. L-Lysine export could be improved fivefold by overexpression of lysE [39,40]. Expression of lysE under control of an L-lysine riboswitch was also applied (see below [43]). 

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KeUe, R., Laufer, B., Brunzema, C., Weuster-Botz, D., Kramer, R., Wandrey, C., 1996. Reaction engineering analysis of L-lysine transport by Corynebacterium glutamicum. Biotechnology and Bioengineering 51 (1), 40-50. 

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