L-alanine exporter, AlaE, of escherichia coli functions as a safety valve to enhance survival under feast conditions

Satoshi Katsube, Tasuke Ando, Hiroshi Yoneyama

    Research output: Contribution to journalArticlepeer-review

    6 Citations (Scopus)


    The intracellular level of amino acids is determined by the balance between their anabolic and catabolic pathways. L-alanine is anabolized by three L-alanine synthesizing enzymes and catabolized by two racemases and D-amino acid dehydrogenase (DadA). In addition, its level is regulated by L-alanine movement across the inner membrane. We identified the novel gene alaE, encoding an L-alanine exporter. To elucidate the physiological function of L-Alanine exporter, AlaE, we determined the susceptibility of alaE-, dadA-, and alaE/dadA-deficient mutants, derived from the wild-type strain MG1655, to L-alanyl-L-alanine (Ala-Ala), which shows toxicity to the L-alanine-nonmetabolizing variant lacking alaE. The dadA-deficient mutant has a similar minimum inhibitory concentration (MIC) (>1.25 mg/mL) to that observed in MG1655. However, alaE-and alaE/dadA-deficient mutants had MICs of 0.04 and 0.0025 mg/mL, respectively. The results suggested that the efficacy of AlaE to relieve stress caused by toxic intracellular accumulation of L-alanine was higher than that of DadA. Consistent with this, the intracellular level of alanine in the alaE-mutant was much higher than that in MG1655 and the dadA-mutant. We, therefore, conclude that AlaE functions as a ‘safety-valve’ to prevent the toxic level accumulation of intracellular L-alanine under a peptide-rich environment, such as within the animal intestine.

    Original languageEnglish
    Article number4942
    JournalInternational journal of molecular sciences
    Issue number19
    Publication statusPublished - 2019 Oct 1


    • AlaE
    • Alanine
    • Coli
    • E

    ASJC Scopus subject areas

    • Catalysis
    • Molecular Biology
    • Spectroscopy
    • Computer Science Applications
    • Physical and Theoretical Chemistry
    • Organic Chemistry
    • Inorganic Chemistry


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