Coordinate genetic regulation of glycogen catabolism and biosynthesis in Escherichia coli via the CsrA gene product

Abstract

The carbon storage regulator gene, csrA, encodes a factor which negatively modulates the expression of the glycogen biosynthetic gene glgC by enhancing the decay of its mRNA (M. Y. Liu, H. Yang, and T. Romeo, J. Bacteriol. 177:2663-2672, 1995). When endogenous glycogen levels in isogenic csrA ؉ and csrA::kanR strains were quantified during the growth curve, both the rate of glycogen accumulation during late exponential or early stationary phase and its subsequent rate of degradation were found to be greatly accelerated by the csrA::kanR mutation. The expression of the biosynthetic genes glgA (glycogen synthase) and glgS was observed to be negatively modulated via csrA. Thus, csrA is now known to control all of the known glycogen biosynthetic genes (glg), which are located in three different operons. Similarly, the expression of the degradative enzyme glycogen phosphorylase, which is encoded by glgY, was found to be negatively regulated via csrA in vivo. The in vitro transcription-translation of glgY was also specifically inhibited by the purified CsrA gene product. These results demonstrate that localization of glycogen biosynthetic and degradative genes within the Escherichia coli glgCAY operon facilitates their coordinate genetic regulation, as previously hypothesized (T. Romeo, A. Kumar, and J. Preiss, Gene 70:363-376, 1988). The csrA gene did not affect glycogen debranching enzyme, which is now shown to be encoded by the gene glgX.One feature of the complex adaptive response which occurs when Escherichia coli or various other bacteria enter stationary phase is the increased expression of genes involved in the biosynthesis of glycogen (reviewed in references 12 and 20-22). A shortage of a nutrient such as nitrogen in the presence of excess carbon is particularly effective in causing the intracellular accumulation of glycogen, which can be metabolized as an endogenous carbon and energy source. The regulatory mechanisms for glycogen synthesis in E. coli include (i) allosteric control via the metabolites AMP and fructose-1,6-bisphosphate of the committed step of the pathway, catalyzed by ADPglucose pyrophosphorylase (EC 2.7.7.27); (ii) stimulation of the genetic expression of glgC (which encodes ADPglucose pyrophosphorylase [2]) and glgA (which encodes glycogen synthase [EC 2.4.1.21] [13]) by guanosine 3Ј-bisphosphate 5Ј-bisphosphate and cyclic AMP (cAMP); and (iii) the transcriptional control of glgS, a monocistronic gene which stimulates glycogen synthesis in vivo, by cAMP and s (9, 20-22, 24, 28). We recently identified and characterized the csrA gene, which exerts a very strong negative effect on glycogen synthesis in E. coli (25,26). This gene encodes a 61-amino-acid protein, CsrA, which was shown to regulate the expression of glgB (encoding glycogen branching enzyme [EC 2.4.1.18]) and glgC (26). CsrA has been shown to be a factor which enhances the rate of decay of glgC mRNA via a novel though unresolved mechanism (16). The deduced amino acid sequence of CsrA is homologous to a diverse subset of RNA-bindin...

Circuitry Linking the Catabolite Repression and Csr Global Regulatory Systems of Escherichia coli

“…By inference, products of carbon metabolism downregulate CsrA activity and glycolytic flux through the Embeden-Meyerhof-Parnas pathway, while they activate gluconeogenesis, glycogen synthesis, synthesis of the biofilm exopolysaccharide dPNAG, and pathways and processes favoring stress resistance and survival, which are repressed by CsrA (Fig. 10) (7,17,18,22,24,33).…”

“…In Escherichia coli, CsrA activates glycolysis and central carbon pathways (7)(8)(9)(10)(11)(12)(13) and motility (14,15). Conversely, it represses gluconeogenesis (7), glycogen biosynthesis (16)(17)(18)(19)(20), biofilm formation (21)(22)(23)(24), the stringent response (25), and expression of genes involved in other stress resistance and stationary-phase processes, e.g., cstA, hfq, cel, sdiA, and nhaR (24,(26)(27)(28)(29)(30). Its effects on pathogenesis are complex.…”

The RNA Molecule CsrB Binds to the Global Regulatory Protein CsrA and Antagonizes Its Activity in Escherichia coli

“…The role of CsrA in procaryotic metabolism and physiology is just beginning to be understood. It is a negative regulator of certain processes associated with the early stationary phase of growth, including glycogen synthesis and catabolism (1,5), and gluconeogenesis (1,4) in E. coli, and the expression of several extracellular virulence factors in E. carotovora (6,7). CsrA also modulates the glycolytic pathway in E. coli (4), affects cell surface properties (1), and has been proposed to directly or indirectly affect DNA gyrase activity (39).…”

“…Studies conducted in vivo have indicated that the CsrA gene product facilitates the decay of glgCAP mRNA, which encodes two enzymes required for glycogen biosynthesis and the enzyme glycogen phosphorylase (3,5). The CsrA gene product is a 61-amino acid protein whose deduced amino acid sequence contains a conserved RNA-binding motif, KH (3).…”

“…Subsequent studies have shown that csrA is a global regulatory gene that controls numerous genes and enzymes of carbohydrate metabolism. In E. coli K-12, it acts as a negative regulator of glycogen biosynthesis, gluconeogenesis, and glycogen catabolism and as a positive factor for glycolysis, and it affects cell surface properties (1,(3)(4)(5). Recent experiments of Chatterjee et al (6) and Cui et al (7) document a key regulatory role for the csrA homolog of the pathogenic Erwinia species, rsmA (repressor of stationary phase metabolites), in the expression of several virulence factors of soft rot disease of higher plants, including pectinase, cellulase, and protease activities, and further suggest that it may modulate the production of the quorum-sensing metabolite N-(3-oxohexanoyl)-L-homoserine lactone.…”