Everything old is new again: an update on current research on the Cpx envelope stress response.

We demonstrate here that Escherichia coli K-12 synthesizes two different L-serine deaminases (L-SD) catalyzing the nonoxidative deamination of L-serine to pyruvate, one coded for by the previously described sdaA gene and a second, hitherto undescribed enzyme which we call L-SD2. A strain carrying a null mutation in sdaA made no detectable L-SD in minimal medium, but had activity in Luria broth. We describe a mutation, sdaX, which affects the regulation of L-SD2 and permits its expression in minimal medium, and an insertion mutation, sdaB, which abolishes L-SD2 activity completely. Both mutations lie near 60.5 min on the E. coli genetic map. The two L-SD enzymes have similar enzyme parameters, and both require posttranslational activation.

A novel L-serine deaminase activity in Escherichia coli K-12.

The sdaB gene which codes for the second l-serine deaminase (L-SD) of Escherichia coli K-12 has been sequenced and shown to be very similar to the sdaA gene which codes for the first l-serine deaminase. sdaB is transcribed in rich medium, particularly in the absence of glucose, and is under the control of catabolite activator protein. A mutation which established expression of the sdaB gene and synthesis of l-serine deaminase 2 in minimal medium has been demonstrated to result in a change in the ribosome-binding site of the sdaB gene.

https://febs.onlinelibrary.wiley.com/doi/pdf/10.1111/j.1432-1033.1993.tb17718.x

Sequencing and characterization of the sdaB gene from Escherichia coli K-12.

Two methods for the direct isolation of spontaneous ssd mutants of Escherichia coli K-12 strains are described; (i) by growth with L-serine as the carbon source, and (ii) by low-level kanamycin resistance. A newly isolated mutant had the same phenotype as the mutant described previously, including inefficient use of the glucose, inability to growth with succinate, altered transport characteristics, and altered resistance to certain growth effectors. Succinate-utilizing derivatives which appear to be intragenic are characterized in detail. The relation between the mutants isolated here and mutants which are thought to have impairment in a system of coupling respiratory energy to active transport (ecfB mutants) is discussed.

L-serine degradation in Escherichia coli K-12: directly isolated ssd mutants and their intragenic revertants.

Strains of Escherichia coli with mutations in the eup (energy-uncoupled phenotype) locus do not grow on nonfermentable carbon sources, have reduced growth yields on limiting glucose, are insensitive to colicins A and K, exhibit resistance to aminoglycoside antibiotics, and are defective in protonmotive force coupled active transport. eup mutations do not result in lowered protonmotive force. Here we show that deenergization of a eup+ strain results in the appearance of a new low KT, low Vmax form of the lactose carrier; in a strain deleted of the eup locus, deenergization does not evoke the low KT, low Vmax form of the lactose carrier. Cells bearing a eup point mutation and exhibiting the Eup- phenotype possess the low KT, low Vmax form of the lactose carrier even when energized. In addition to affecting the kinetic parameters of the lactose carrier, the eup point mutation also reduces the KT and Vmax of the proline carrier. On the basis of these findings, we suggest that the normal eup gene product mediates a novel regulation of lactose carrier function following deenergization. The defect in proline and lactose transport caused by eup point mutations may stem from an altered eup product aberrantly mediating the regulation under energized conditions. Finally, the pleiotropy associated with eup point mutations may be indicative of those protonmotive force driven functions that are subject to eup regulation.

Evidence for a protonmotive force related regulatory system in Escherichia coli and its effects on lactose transport.

The effects of a pleiotropic mutation ssd are described. This mutation results in decreased efficiency in the use of glucose and fructose as carbon source, inability to use succinate or to grow anaerobically, an alteration in the activity of enzymes responsible for the synthesis and degradation of L-serine, increased resistance to certain antibiotics, and a deficiency in proline transport. This mutation resembles various previously described mutations throught to affect ‘energy coupling factor’ and is located in the same region of the chromosome. While the gene product affected by this mutation is still unidentified, it is clear that L-serine metabolism cannot be understood merely in terms of providing L-serine and its derivatives.

A mutation affecting L-serine and energy metabolism in E. coli K12

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A mutation affecting L-serine and energy metabolism in E. coli K12