Three Kinds of Controls Affecting the Expression of the glp Regulon in Escherichia coli

Abstract

Three kinds of control mechanisms govern the expression of the members of the glp regulon for glycerol and sn-glycerol 3-phosphate (G3P) catabolism in Escherichia coli K-12: specific repression by the product of the glpR gene; catabolite repression; and respiratory repression (the effect exerted by exogenous hydrogen acceptors). The operons of the glp system show different patterns of response to each control. By growing in parallel a mutant strain with temperature-sensitive repressor (glpRt8) and an isogenic control with a deletion in the regulator gene at progressively higher temperatures, it was possible to show that the synthesis of aerobic G3P dehydrogenase (glpD product) is far more sensitive to specific repression than that of either glycerol kinase (glpK product) or G3P transport (glpT product). Conversely, in the strain with a deletion in the regulator gene, the syntheses of glycerol kinase and G3P transport are more sensitive to catabolite repression than that of the aerobic G3P dehydrogenase. The levels of the two flavoprotein G3P dehydrogenases vary in opposite directions in response to changes of exogenous hydrogen acceptors. For example, the ratio of the aerobic enzyme to the anaerobic enzyme (specified by gipA) is high when molecular oxygen or nitrate serves as the hydrogen acceptor and low when fumarate plays this role. This trend is not influenced by the addition of cyclic adenosine 3', 5'-monophosphate to the growth medium. Thus, respiratory repression most likely involves a third mechanism of control, independent of specific or catabolite repression.

Transketolase activity modulates glycerol‐3‐phosphate levels in Escherichia coli

“…2A). Catabolite repression of glpFKX operon (Freedberg and Lin, 1973;Weissenborn et al, 1992), may account for the lack of induction by glycerol in LB medium.…”

Metabolic and regulatory rearrangements underlying glycerol metabolism in Pseudomonas putida KT2440

“…1B). Previous in silico predictions had suggested that the promoters of the glp regulon share a common regulatory motif in different Gram-negative bacteria (Freedberg and Lin, 1973;Schweizer and Po, 1996;Danilova et al, 2003) and that glpR, glpK and glpF might form an operon (Mao et al, 2009). However, the sequence coverage plots demonstrated that this is not the case, as two distinct transcriptional units were clearly identified; one of them encompassed glpF and glpK, whereas glpD was independently transcribed.…”

Cloning of the glycerol kinase gene of Bacillus subtilis

“…In the glycerol kinase assay, phosphorylation of glycerol was coupled to reduction of NAD + by NAD-dependent L-c~-G3P dehydrogenase from rabbit muscle. The assay was performed at 25°C essentially as described by Freedberg and Lin [7]. By using a buffer with pH 9.0 instead of 9.5, more reproducible results were obtained.…”

“…The glp genes are repressed to various degrees by a protein repressor and require G3P for full expression. The glp genes are also subject to glucose and catabolite repression [7,8]. In other bacteria than E. coli relatively little is known about the organization and regulation of genes involved in glycerol catabolism.…”