Identification of a new gene yecC involved in threonine export in Escherichia coli

Threonine (Thr), an essential amino acid for mammals, has expanded its application to industries with fast-growing market demand. One factor that limits the production of L-threonine by microbial fermentation is the lack of an effective export system. This study proposes a method based on isobaric tags for relative and absolute quantification (iTRAQ) to determine potential Thr excretion proteins. Proteomics analysis revealed that an ABC family transport protein named YecC was upregulated in response to Thr addition. When the yecC gene or yecC-yecS-fliY is overexpressed in Escherichia coli DH5α, a phenotype resistant to inhibitory concentrations of Thr was observed in the strains. In addition, Thr production was increased when the yecC gene and yecC-yecS-fliY were overexpressed in the Thr producers in which rthA or rthBC was deleted separately or in combination. Therefore, YecC protein could facilitate Thr efflux in E. coli and be suitable for application in engineering microbial cells to produce Thr.