Export of l -Isoleucine from Corynebacterium glutamicum : a Two-Gene-Encoded Member of a New Translocator Family

Abstract

Bacteria possess amino acid export systems, and Corynebacterium glutamicum excretes L-isoleucine in a process dependent on the proton motive force. In order to identify the system responsible for L-isoleucine export, we have used transposon mutagenesis to isolate mutants of C. glutamicum sensitive to the peptide isoleucyl-isoleucine. In one such mutant, strong peptide sensitivity resulted from insertion into a gene designated brnF encoding a hydrophobic protein predicted to possess seven transmembrane spanning helices. brnE is located downstream of brnF and encodes a second hydrophobic protein with four putative membrane-spanning helices. A mutant deleted of both genes no longer exports L-isoleucine, whereas an overexpressing strain exports this amino acid at an increased rate. BrnF and BrnE together are also required for the export of L-leucine and L-valine. BrnFE is thus a two-component export permease specific for aliphatic hydrophobic amino acids. Upstream of brnFE and transcribed divergently is an Lrp-like regulatory gene required for active export. Searches for homologues of BrnFE show that this type of exporter is widespread in prokaryotes but lacking in eukaryotes and that both gene products which together comprise the members of a novel family, the LIV-E family, generally map together within a single operon. Comparisons of the BrnF and BrnE phylogenetic trees show that gene duplication events in the early bacterial lineage gave rise to multiple paralogues that have been retained in ␣-proteobacteria but not in other prokaryotes analyzed.

Syntrophic exchange in synthetic microbial communities

“…Our E. coli genome encodes several amino acid exporters for excretion of different amino acids including L-threonine (RhtA and RhtC) (26), L-leucine (YeaS) (29), L-aromatic amino acids (YddG) (30), L-arginine (YggA) (31), L-alanine (alaE) (32), and L-homoserine (RhtB) (26). Other exporters have been documented in related organisms including lysE for L-lysine export and brnFE for L-isoleucine and L-methionine export in Corynebacterium glutamicum (33,34). In addition to active transport, some level of passive transport may also be involved because hydrophobic amino acids such as I, F, Y, and W have membrane permeability that is 100 times greater than hydrophilic amino acids (35).…”

Metabolic engineering of Escherichia coli for the production of l -valine based on transcriptome analysis and in silico gene knockout simulation

“…The E. coli genes homologous to brnFE were suggested to be the ygaZH genes by homology search (29). The amino acid sequence of YgaZ showed 27% identity to that of BrnF (SI Fig.…”

“…In C. glutamicum, which is the most widely used bacterium for amino acid production, the brnFE genes encode the exporter of branched-chain amino acids (29). The E. coli genes homologous to brnFE were suggested to be the ygaZH genes by homology search (29).…”

A leuC mutation leading to increased L-lysine production and rel-independent global expression changes in Corynebacterium glutamicum

“…The Lrp is a global regulator in E. coli, affecting the expressions of many genes and operons including the catabolism and anabolism of amino acids (Newman et al 1996). In C. glutamicum, an Lrp-type transcription factor is located adjacent to the brnFE operon which codes for L-isoleucine-and L-methionine-export protein and is known to be responsible for regulation of the operon (Kennerknecht et al 2002;Trötschel et al 2005). We evaluated the effect of deletion of lrp on both L-lysine production and transcriptome.…”