Aerobic regulation of the sucABCD genes of Escherichia coli, which encode alpha-ketoglutarate dehydrogenase and succinyl coenzyme A synthetase: roles of ArcA, Fnr, and the upstream sdhCDAB promoter

Abstract

The sucABCD genes of Escherichia coli encode subunits for two enzymes of the tricarboxylic acid (TCA) cycle, ␣-ketoglutarate dehydrogenase (sucAB) and succinyl coenzyme A synthetase (sucCD). To examine how these genes are expressed in response to changes in oxygen and carbon availability, a set of sucA-lacZ, sucC-lacZ, sdhCDAB-sucA-lacZ, and sdhC-lacZ fusions were constructed and analyzed in vivo. While the expression of a sucA-lacZ fusion was low under all cell growth conditions tested, the expression of the sucA gene from the upstream sdhC promoter was considerably higher and varied by up to 14-fold depending on the carbon substrate used. Expression of the sdhCDAB-sucA-lacZ fusion varied by fourfold in response to oxygen. In contrast, no expression was seen from a sucC-lacZ reporter fusion, indicating that no promoter immediately precedes the sucCD genes. Taken together, these findings demonstrate that the oxygen and carbon control of sucABCD gene expression occurs by transcriptional regulation of the upstream sdhC promoter. The weaker sucA promoter provides an additional low constitutive level of sucABCD gene expression to supplement transcription from the sdhC promoter. The negative control of sucABCD gene expression seen under anaerobic conditions, like that for the sdhCDAB genes, is provided by the arcA and fnr gene products. These findings establish that the differential expression of eight genes for three of the TCA cycle enzymes in E. coli is controlled from one regulatory element.The two tricarboxylic acid (TCA) cycle enzymes in Escherichia coli, ␣-ketoglutarate dehydrogenase and succinyl coenzyme A synthetase (succinyl-CoA synthetase), are encoded by thesucAB and sucCD genes, respectively (4). ␣-Ketoglutarate dehydrogenase catalyzes the oxidative decarboxylation of ␣-ketoglutarate to generate succinyl-CoA and carbon dioxide, along with the production of NADH plus H ϩ (20). SuccinylCoA synthetase catalyzes the interconversion of succinyl-CoA and succinate, and this interconversion is accompanied by the production or hydrolysis of GTP (10, 15). Both TCA cycle enzymes participate in the cyclic flow of carbon from acetylCoA to carbon dioxide during aerobic cell growth conditions (4). This process provides reducing equivalents in the form of NADH for subsequent use in electron transport-linked phosphorylation reactions. Succinyl-CoA synthetase also participates in the noncyclic or branched pathway operative during anaerobic cell growth conditions to provide carbon intermediates for cell biosynthetic reactions (10, 15). The results of enzyme assays and two-dimensional protein gel electrophoresis studies indicate that the cellular synthesis of ␣-ketoglutarate dehydrogenase is suppressed by anaerobiosis and glucose and is induced by acetate or other oxidized carbon sources (1,5,24).The sucABCD genes are located at 16.7 min in the E. coli chromosome near the genes for two other TCA cycle enzymes, succinate dehydrogenase (sdhCDAB) and citrate synthase (gltA) (Fig. 1) (25). Little information is available concer...

The Acetate Switch

“…In the absence of oxygen, the oxygen-sensitive global regulators ArcA and FNR mediate the repression of many TCA promoters, but most dramatically the sdh-suc operon, which encodes SDH, KDGH, and the SCSC (104,105,170,293,335,339,406). The mechanism that causes glucose repression, and thus the Crabtree effect, is less clear.…”

“…A more moderate inhibition occurs in the presence of excess glucose (160,170,193,212,(335)(336)(337)(338)(339)413).…”

YgfX (CptA) is a multimeric membrane protein that interacts with the succinate dehydrogenase assembly factor SdhE (YgfY)

“…Metabolic enzymes, such as SDH, are tightly regulated so they function only when required (Cecchini et al, 2002;Park et al, 1995Park et al, , 1997. We previously identified SdhE and demonstrated that it is a soluble cytoplasmic protein required for SdhA flavinylation and activation of SDH (McNeil et al, 2012).…”

Investigation of in vivo cross-talk between key two-component systems of Escherichia coli

“…This latter enzyme uses phosphate as a substrate to generate ATP (Wanner, 1995). Expression of sucCD is controlled from the sdh promoter (Park et al, 1997). So decreasing sucCD expression, due to substrate (i.e.…”