A new oxygen-regulated operon in Escherichia coli comprises the genes for a putative third cytochrome oxidase and for pH 2.5 acid phosphatase (appA)

Abstract

The Escherichia coli acid phosphatase gene appA is expressed in response to oxygen deprivation and is positively controlled by the product of appR (katF) which encodes a putative new sigma transcription-initiation factor. However, transcription of appA from its nearest promoter (P1) did not account for total pH 2.5 acid phosphatase expression and was not subject to regulation. The cloned region upstream of appA was extended and analyzed by insertions of transposon TnphoA and by fusions with lacZ. It contains two new genes, appC and appB, which both encode extracytoplasmic proteins. appC and appB are expressed from a promoter (P2) lying just upstream of appC. Both genes are regulated by oxygen, as is appA, and by appR gene product exactly as previously shown for appA. Analysis of the nucleotide sequence and of the origins of transcription have confirmed that the P2-appC-appB- (ORFX)-P1-appA region is organized on the chromosome as an operon transcribed clockwise from P2 and that P1 is a minor promoter for appA alone. Genes appC and appB encode proteins of Mr 58,133 and 42,377, respectively, which have the characteristics of integral membrane proteins. The deduced amino acid sequences of appC and appB show 60% and 57% homology, respectively, with subunits I and II of the E. coli cytochrome d oxidase (encoded by genes cydA and cydB). The notion that the AppC and AppB proteins constitute a new cytochrome oxidase or a new oxygen-detoxifying system is supported by the observation of enhanced sensitivity to oxygen of mutants lacking all three genes, cyo (cytochrome o oxidase), cyd (cytochrome d oxidase) and appB, compared to that of cyo cyd double mutants.

Compensations for Diminished Terminal Oxidase Activity in Escherichia coli

“…The sequence similarities between AppC and CydA and between AppB and CydB are striking (3), and the matching overlay of hydrophobicity plots for subunits I (AppC/CydA) and II (AppB/CydB) (3) suggests that their insertion in the membrane is likely to be in the same direction. Furthermore, gene fusion studies with appB suggest that this subunit is inserted in the membrane in the same orientation as CydB (3).…”

“…Furthermore, gene fusion studies with appB suggest that this subunit is inserted in the membrane in the same orientation as CydB (3). If this is the case, then AppBC presumably exhibits an adaptation to enable deposition of the quinol-derived protons into the cytoplasm while consuming two cytoplasmic protons during the reduction of molecular oxygen (Fig.…”

“…Additionally, the appBC locus of E. coli has been shown to encode a terminal oxidase of the cytochrome bd type (cytochrome bd-II) (3,4). Both cytochrome bd-I (CydAB) and cytochrome bd-II (AppBC) are quinol oxidases, each comprising two polypeptides and a low spin heme b, high spin heme b, and heme d (4 -6).…”

Nitrate and nitrite transport in bacteria

“…able inhibition of nitrate reduction by oxygen in the absence of oxidases was still observed, which may be due to the activity of a third E. coli oxidase [8], or there may be a distinct effect of oxygen on nitrate/nitrite transport evident in these strains. Kucera and co-workers [9] measured internally accumulated nitrate in whole cells of P. denitrificans.…”

Aeration‐dependent changes in composition of the quinone pool in Escherichia coli

“…Arc and Fnr [1]. This regulatory duet has been recently replenished with one more regulatory system, AppY, which takes part in aeration-dependent expression of hya operon (encoding for hydrogenase I), and appA operon (encoding for an acid phosphatase and the third putative terminal oxidase of Escherichia coli with large sequence similarities to the bd type oxidase) [2][3][4][5].…”