The gene yghK linked to the glc operon of Escherichia coli encodes a permease for glycolate that is structurally and functionally similar to L-lactate permease

Abstract

In Escherichia coli the glc operon involved in glycolate utilization is located at 673 min and formed by genes encoding the enzymes glycolate oxidase (glcDEF) and malate synthase G (glcB). Their expression from a single promoter upstream of glcD is induced by growth on glycolate and regulated by the activator encoded by the divergently transcribed gene glcC. Gene yghK, located 350 bp downstream of glcB, encodes a hydrophobic protein highly similar to the L-lactate permease encoded by lldP. Expression studies have shown that the yghK gene (proposed name glcA) is transcribed from the same promoter as the other glc structural genes and thus belongs to the glc operon. Characterization of a glcA ::cat mutant showed that GlcA acts as glycolate permease and that glycolate can also enter the cell through another transport system. Evidence is presented of the involvement of L-lactate permease in glycolate uptake. Growth on this compound was abolished in a double mutant of the paralogous genes glcA and lldP, and restored with plasmids expressing either GlcA or LldP. Characterization of the putative substrates for these two related permeases showed, in both cases, specificity for the 2-hydroxymonocarboxylates glycolate, L-lactate and D-lactate. Although both GlcA and LldP recognize D-lactate, mutant analysis proved that L-lactate permease is mainly responsible for its uptake.

The Gene yjcG , Cotranscribed with the Gene acs , Encodes an Acetate Permease in Escherichia coli

“…Cells of strain JA202 carrying mutations in the glcA and lldP genes encoding the glycolate and lactate transporters, respectively, do not grow on glycolate (21). However, spontaneous mutants of strain JA202 able to grow on glycolate were isolated.…”

“…The overlapping specificity of LldP and GlcA explains why a glycolate or L-lactate entry-negative phenotype requires inactivation of both transporters (21). In this study we analyzed the appearance in an lldP glcA double mutant of another transport system for the two-carbon carboxylate glycolate, which is also able to transport acetate.…”

“…The 2-hydroxymonocarboxylic acids L-lactate, D-lactate, and glycolate share the transporters encoded by two genes, lldP of the lactate operon and glcA of the glycolate operon (21). Both transporters accumulate their substrates against a concentration gradient driven by a proton motive force.…”

Dual Role of LldR in Regulation of the lldPRD Operon, Involved in l -Lactate Metabolism in Escherichia coli

“…The lldD gene encodes the dehydrogenase, lldP encodes the permease, and lldR encodes a regulatory protein (4). Although L-lactate is also recognized by the permease encoded by glcA, the lack of induction of this gene by growth on L-lactate indicates that LldP mediates the uptake of L-lactate in vivo (18,19).…”

Identification of the Genes That Contribute to Lactate Utilization in Helicobacter pylori

“…In E. coli , the lctP -encoding permease protein shares a high degree of similarity to the product of yghK ( glcA ) gene in glycolate utilization operon. Because of structural and functional similarities, both LctP and GlcA are able to transport glycolate as well as D- and L-lactate in a proton motive force dependent manner [23], [24]. This mechanism is likely not applicable to H. pylori as no GlcA orthologue has been found in its genome; conversely, in H. pylori LctP could function in glycolate transport as glycolate oxidase is present in this bacterium (GlcD; HP0509/JHP459) [7], [9].…”